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Comprehensive Python Cheatsheet
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1. Collections: List,Dictionary,Set,Tuple,Range,Enumerate,Iterator,Generator.
2. Types: Type,String,Regular_Exp,Format,Numbers,Combinatorics,Datetime.
3. Syntax: Args,Inline,Closure,Decorator,Class,Duck_Type,Enum,Exception.
4. System: Exit,Print,Input,Command_Line_Arguments,Open,Path,OS_Commands.
5. Data: JSON,Pickle,CSV,SQLite,Bytes,Struct,Array,Memory_View,Deque.
6. Advanced: Threading,Operator,Introspection,Metaprograming,Eval,Coroutines.
7. Libraries: Progress_Bar,Plot,Table,Curses,Logging,Scraping,Web,Profile,
NumPy,Image,Audio,Games,Data,Cython.
if__name__=='__main__':# Runs main() if file wasn't imported.main()
<list>=<list>[from_inclusive :to_exclusive : ±step_size]
<list>.append(<el>)# Or: <list> += [<el>]<list>.extend(<collection>)# Or: <list> += <collection>
<list>.sort()<list>.reverse()<list>=sorted(<collection>)<iter>=reversed(<list>)
sum_of_elements=sum(<collection>)elementwise_sum= [sum(pair)forpairinzip(list_a,list_b)]sorted_by_second=sorted(<collection>,key=lambdael:el[1])sorted_by_both=sorted(<collection>,key=lambdael: (el[1],el[0]))flatter_list=list(itertools.chain.from_iterable(<list>))product_of_elems=functools.reduce(lambdaout,el:out*el,<collection>)list_of_chars=list(<str>)
- Moduleoperator provides functions itemgetter() and mul() that offer the same functionality aslambda expressions above.
<int>=<list>.count(<el>)# Returns number of occurrences. Also works on strings.index=<list>.index(<el>)# Returns index of first occurrence or raises ValueError.<list>.insert(index,<el>)# Inserts item at index and moves the rest to the right.<el>=<list>.pop([index])# Removes and returns item at index or from the end.<list>.remove(<el>)# Removes first occurrence of item or raises ValueError.<list>.clear()# Removes all items. Also works on dictionary and set.
<view>=<dict>.keys()# Coll. of keys that reflects changes.<view>=<dict>.values()# Coll. of values that reflects changes.<view>=<dict>.items()# Coll. of key-value tuples that reflects chgs.
value=<dict>.get(key,default=None)# Returns default if key is missing.value=<dict>.setdefault(key,default=None)# Returns and writes default if key is missing.<dict>=collections.defaultdict(<type>)# Creates a dict with default value of type.<dict>=collections.defaultdict(lambda:1)# Creates a dict with default value 1.
<dict>=dict(<collection>)# Creates a dict from coll. of key-value pairs.<dict>=dict(zip(keys,values))# Creates a dict from two collections.<dict>=dict.fromkeys(keys [,value])# Creates a dict from collection of keys.
<dict>.update(<dict>)# Adds items. Replaces ones with matching keys.value=<dict>.pop(key)# Removes item or raises KeyError.{kfork,vin<dict>.items()ifv==value}# Returns set of keys that point to the value.{k:vfork,vin<dict>.items()ifkinkeys}# Returns a dictionary, filtered by keys.
>>>fromcollectionsimportCounter>>>colors= ['blue','blue','blue','red','red']>>>counter=Counter(colors)>>>counter['yellow']+=1Counter({'blue':3,'red':2,'yellow':1})>>>counter.most_common()[0]('blue',3)
<set>=set()
<set>.add(<el>)# Or: <set> |= {<el>}<set>.update(<collection>)# Or: <set> |= <set>
<set>=<set>.union(<coll.>)# Or: <set> | <set><set>=<set>.intersection(<coll.>)# Or: <set> & <set><set>=<set>.difference(<coll.>)# Or: <set> - <set><set>=<set>.symmetric_difference(<coll.>)# Or: <set> ^ <set><bool>=<set>.issubset(<coll.>)# Or: <set> <= <set><bool>=<set>.issuperset(<coll.>)# Or: <set> >= <set>
<el>=<set>.pop()# Raises KeyError if empty.<set>.remove(<el>)# Raises KeyError if missing.<set>.discard(<el>)# Doesn't raise an error.
- Is immutable and hashable.
- That means it can be used as a key in a dictionary or as an element in a set.
<frozenset>=frozenset(<collection>)
Tuple is an immutable and hashable list.
<tuple>= ()<tuple>= (<el>, )<tuple>= (<el_1>,<el_2> [, ...])
Tuple's subclass with named elements.
>>>fromcollectionsimportnamedtuple>>>Point=namedtuple('Point','x y')>>>p=Point(1,y=2)Point(x=1,y=2)>>>p[0]1>>>p.x1>>>getattr(p,'y')2>>>p._fields# Or: Point._fields('x','y')
<range>=range(to_exclusive)<range>=range(from_inclusive,to_exclusive)<range>=range(from_inclusive,to_exclusive, ±step_size)
from_inclusive=<range>.startto_exclusive=<range>.stop
fori,elinenumerate(<collection> [,i_start]): ...
<iter>=iter(<collection>)# `iter(<iter>)` returns unmodified iterator.<iter>=iter(<function>,to_exclusive)# A sequence of return values until 'to_exclusive'.<el>=next(<iter> [,default])# Raises StopIteration or returns 'default' on end.<list>=list(<iter>)# Returns a list of iterator's remaining elements.
fromitertoolsimportcount,repeat,cycle,chain,islice
<iter>=count(start=0,step=1)# Returns updated value endlessly. Accepts floats.<iter>=repeat(<el> [,times])# Returns element endlessly or 'times' times.<iter>=cycle(<collection>)# Repeats the sequence endlessly.
<iter>=chain(<coll_1>,<coll_2> [, ...])# Empties collections in order.<iter>=chain.from_iterable(<collection>)# Empties collections inside a collection in order.
<iter>=islice(<collection>,to_exclusive)<iter>=islice(<collection>,from_inclusive,to_exclusive [,+step_size])
- Any function that contains a yield statement returns a generator.
- Generators and iterators are interchangeable.
defcount(start,step):whileTrue:yieldstartstart+=step
>>>counter=count(10,2)>>>next(counter),next(counter),next(counter)(10,12,14)
- Everything is an object.
- Every object has a type.
- Type and class are synonymous.
<type>=type(<el>)# Or: <el>.__class__<bool>=isinstance(<el>,<type>)# Or: issubclass(type(<el>), <type>)
>>>type('a'),'a'.__class__,str(<class'str'>,<class'str'>,<class'str'>)
fromtypesimportFunctionType,MethodType,LambdaType,GeneratorType
Each abstract base class specifies a set of virtual subclasses. These classes are then recognized by isinstance() and issubclass() as subclasses of the ABC, although they are really not.
>>>fromcollections.abcimportSequence,Collection,Iterable>>>isinstance([1,2,3],Iterable)True
+------------------+------------+------------+------------+| | Sequence | Collection | Iterable |+------------------+------------+------------+------------+| list, range, str | yes | yes | yes || dict, set | | yes | yes || iter | | | yes |+------------------+------------+------------+------------+>>>fromnumbersimportIntegral,Rational,Real,Complex,Number>>>isinstance(123,Number)True
+--------------------+----------+----------+----------+----------+----------+| | Integral | Rational | Real | Complex | Number |+--------------------+----------+----------+----------+----------+----------+| int | yes | yes | yes | yes | yes || fractions.Fraction | | yes | yes | yes | yes || float | | | yes | yes | yes || complex | | | | yes | yes || decimal.Decimal | | | | | yes |+--------------------+----------+----------+----------+----------+----------+<str>=<str>.strip()# Strips all whitespace characters from both ends.<str>=<str>.strip('<chars>')# Strips all passed characters from both ends.
<list>=<str>.split()# Splits on one or more whitespace characters.<list>=<str>.split(sep=None,maxsplit=-1)# Splits on 'sep' str at most 'maxsplit' times.<list>=<str>.splitlines(keepends=False)# Splits on \n,\r,\r\n. Keeps them if 'keepends'.<str>=<str>.join(<coll_of_strings>)# Joins elements using string as separator.
<bool>=<sub_str>in<str># Checks if string contains a substring.<bool>=<str>.startswith(<sub_str>)# Pass tuple of strings for multiple options.<bool>=<str>.endswith(<sub_str>)# Pass tuple of strings for multiple options.<int>=<str>.find(<sub_str>)# Returns start index of first match or -1.<int>=<str>.index(<sub_str>)# Same but raises ValueError if missing.
<str>=<str>.replace(old,new [,count])# Replaces 'old' with 'new' at most 'count' times.<str>=<str>.translate(<table>)# Use `str.maketrans(<dict>)` to generate table.
<str>=chr(<int>)# Converts int to Unicode char.<int>=ord(<str>)# Converts Unicode char to int.
- Also:
'lstrip()','rstrip()'. - Also:
'lower()','upper()','capitalize()'and'title()'.
+---------------+----------+----------+----------+----------+----------+| | [ !#$%…] | [a-zA-Z] | [¼½¾] | [²³¹] | [0-9] |+---------------+----------+----------+----------+----------+----------+| isprintable() | yes | yes | yes | yes | yes || isalnum() | | yes | yes | yes | yes || isnumeric() | | | yes | yes | yes || isdigit() | | | | yes | yes || isdecimal() | | | | | yes |+---------------+----------+----------+----------+----------+----------+- Also:
'isspace()'checks for'[ \t\n\r\f\v…]'.
importre<str>=re.sub(<regex>,new,text,count=0)# Substitutes all occurrences with 'new'.<list>=re.findall(<regex>,text)# Returns all occurrences as strings.<list>=re.split(<regex>,text,maxsplit=0)# Use brackets in regex to include the matches.<Match>=re.search(<regex>,text)# Searches for first occurrence of the pattern.<Match>=re.match(<regex>,text)# Searches only at the beginning of the text.<iter>=re.finditer(<regex>,text)# Returns all occurrences as match objects.
- Search() and match() return None if they can't find a match.
- Argument
'flags=re.IGNORECASE'can be used with all functions. - Argument
'flags=re.MULTILINE'makes'^'and'$'match the start/end of each line. - Argument
'flags=re.DOTALL'makes dot also accept the'\n'. - Use
r'\1'or'\\1'for backreference. - Add
'?'after an operator to make it non-greedy.
<str>=<Match>.group()# Returns the whole match. Also group(0).<str>=<Match>.group(1)# Returns part in the first bracket.<tuple>=<Match>.groups()# Returns all bracketed parts.<int>=<Match>.start()# Returns start index of the match.<int>=<Match>.end()# Returns exclusive end index of the match.
- By default digits, alphanumerics and whitespaces from all alphabets are matched, unless
'flags=re.ASCII'argument is used. - Use a capital letter for negation.
'\d'=='[0-9]'# Matches any digit.'\w'=='[a-zA-Z0-9_]'# Matches any alphanumeric.'\s'=='[\t\n\r\f\v]'# Matches any whitespace.
<str>= f'{<el_1>}, {<el_2>}'<str> = '{}, {}'.format(<el_1>,<el_2>)
>>>fromcollectionsimportnamedtuple>>>Person=namedtuple('Person','name height')>>>person=Person('Jean-Luc',187)>>>f'{person.height}''187'>>>'{p.height}'.format(p=person)'187'
{<el>:<10}# '<el> '{<el>:^10}# ' <el> '{<el>:>10}# ' <el>'{<el>:.<10}# '<el>......'{<el>:<0}# '<el>''!r' calls object'srepr() method, instead ofstr(), to get a string.
{'abcde'!r:10}# "'abcde' "{'abcde':10.3}# 'abc '{'abcde':.3}# 'abc'{123456:10,}# ' 123,456'{123456:10_}# ' 123_456'{123456:+10}# ' +123456'{-123456:=10}# '- 123456'{123456: }# ' 123456'{-123456: }# '-123456'{1.23456:10.3}# ' 1.23'{1.23456:10.3f}# ' 1.235'{1.23456:10.3e}# ' 1.235e+00'{1.23456:10.3%}# ' 123.456%'+---------------+-----------------+-----------------+-----------------+-----------------+| | {<float>} | {<float>:f} | {<float>:e} | {<float>:%} |+---------------+-----------------+-----------------+-----------------+-----------------+| 0.000056789 | '5.6789e-05' | '0.000057' | '5.678900e-05' | '0.005679%' || 0.00056789 | '0.00056789' | '0.000568' | '5.678900e-04' | '0.056789%' || 0.0056789 | '0.0056789' | '0.005679' | '5.678900e-03' | '0.567890%' || 0.056789 | '0.056789' | '0.056789' | '5.678900e-02' | '5.678900%' || 0.56789 | '0.56789' | '0.567890' | '5.678900e-01' | '56.789000%' || 5.6789 | '5.6789' | '5.678900' | '5.678900e+00' | '567.890000%' || 56.789 | '56.789' | '56.789000' | '5.678900e+01' | '5678.900000%' || 567.89 | '567.89' | '567.890000' | '5.678900e+02' | '56789.000000%' |+---------------+-----------------+-----------------+-----------------+-----------------++---------------+-----------------+-----------------+-----------------+-----------------+| | {<float>:.2} | {<float>:.2f} | {<float>:.2e} | {<float>:.2%} |+---------------+-----------------+-----------------+-----------------+-----------------+| 0.000056789 | '5.7e-05' | '0.00' | '5.68e-05' | '0.01%' || 0.00056789 | '0.00057' | '0.00' | '5.68e-04' | '0.06%' || 0.0056789 | '0.0057' | '0.01' | '5.68e-03' | '0.57%' || 0.056789 | '0.057' | '0.06' | '5.68e-02' | '5.68%' || 0.56789 | '0.57' | '0.57' | '5.68e-01' | '56.79%' || 5.6789 | '5.7' | '5.68' | '5.68e+00' | '567.89%' || 56.789 | '5.7e+01' | '56.79' | '5.68e+01' | '5678.90%' || 567.89 | '5.7e+02' | '567.89' | '5.68e+02' | '56789.00%' |+---------------+-----------------+-----------------+-----------------+-----------------+{90:c}# 'Z'{90:b}# '1011010'{90:X}# '5A'<int>=int(<float/str/bool>)# Or: math.floor(<float>)<float>=float(<int/str/bool>)# Or: <real>e±<int><complex>=complex(real=0,imag=0)# Or: <real> ± <real>j<Fraction>=fractions.Fraction(0,1)# Or: Fraction(numerator=0, denominator=1)<Decimal>=decimal.Decimal(<str/int>)# Or: Decimal((sign, digits, exponent))
'int(<str>)'and'float(<str>)'raise ValueError on malformed strings.- Decimal numbers can be represented exactly, unlike floats where
'1.1 + 2.2 != 3.3'. - Precision of decimal operations is set with:
'decimal.getcontext().prec = <int>'.
<num>=pow(<num>,<num>)# Or: <num> ** <num><num>=abs(<num>)# <float> = abs(<complex>)<num>=round(<num> [, ±ndigits])# `round(126, -1) == 130`
frommathimporte,pi,inf,nan,isinf,isnanfrommathimportcos,acos,sin,asin,tan,atan,degrees,radiansfrommathimportlog,log10,log2
fromstatisticsimportmean,median,variance,stdev,pvariance,pstdev
fromrandomimportrandom,randint,choice,shuffle<float>=random()<int>=randint(from_inclusive,to_inclusive)<el>=choice(<list>)shuffle(<list>)
<int>= ±0b<bin># Or: ±0x<hex><int>=int('±<bin>',2)# Or: int('±<hex>', 16)<int>=int('±0b<bin>',0)# Or: int('±0x<hex>', 0)<str>=bin(<int>)# Returns '[-]0b<bin>'.
<int>=<int>&<int># And<int>=<int>|<int># Or<int>=<int>^<int># Xor (0 if both bits equal)<int>=<int><<n_bits# Shift left (>> for right)<int>=~<int># Not (also: -<int> - 1)
- Every function returns an iterator.
- If you want to print the iterator, you need to pass it to the list() function first!
fromitertoolsimportproduct,combinations,combinations_with_replacement,permutations
>>>product([0,1],repeat=3)[(0,0,0), (0,0,1), (0,1,0), (0,1,1), (1,0,0), (1,0,1), (1,1,0), (1,1,1)]
>>>product('ab','12')[('a','1'), ('a','2'), ('b','1'), ('b','2')]
>>>combinations('abc',2)[('a','b'), ('a','c'), ('b','c')]
>>>combinations_with_replacement('abc',2)[('a','a'), ('a','b'), ('a','c'), ('b','b'), ('b','c'), ('c','c')]
>>>permutations('abc',2)[('a','b'), ('a','c'), ('b','a'), ('b','c'), ('c','a'), ('c','b')]
- Module 'datetime' provides 'date'
<D>, 'time'<T>, 'datetime'<DT>and 'timedelta'<TD>classes. All are immutable and hashable. - Time and datetime objects can be 'aware'
<a>, meaning they have defined timezone, or 'naive'<n>, meaning they don't. - If object is naive, it is presumed to be in the system's timezone.
fromdatetimeimportdate,time,datetime,timedeltafromdateutil.tzimportUTC,tzlocal,gettz,resolve_imaginary
<D>=date(year,month,day)<T>=time(hour=0,minute=0,second=0,microsecond=0,tzinfo=None,fold=0)<DT>=datetime(year,month,day,hour=0,minute=0,second=0, ...)<TD>=timedelta(days=0,seconds=0,microseconds=0,milliseconds=0,minutes=0,hours=0,weeks=0)
- Use
'<D/DT>.weekday()'to get the day of the week (Mon == 0). 'fold=1'means the second pass in case of time jumping back for one hour.'<DTa> = resolve_imaginary(<DTa>)'fixes DTs that fall into the missing hour.
<D/DTn>=D/DT.today()# Current local date or naive datetime.<DTn>=DT.utcnow()# Naive datetime from current UTC time.<DTa>=DT.now(<tzinfo>)# Aware datetime from current tz time.
- To extract time use
'<DTn>.time()','<DTa>.time()'or'<DTa>.timetz()'.
<tzinfo>=UTC# UTC timezone. London without DST.<tzinfo>=tzlocal()# Local timezone. Also gettz().<tzinfo>=gettz('<Continent>/<City>')# 'Continent/City_Name' timezone or None.<DTa>=<DT>.astimezone(<tzinfo>)# Datetime, converted to passed timezone.<Ta/DTa>=<T/DT>.replace(tzinfo=<tzinfo>)# Unconverted object with new timezone.
<D/T/DT>=D/T/DT.fromisoformat('<iso>')# Object from ISO string. Raises ValueError.<DT>=DT.strptime(<str>,'<format>')# Datetime from str, according to format.<D/DTn>=D/DT.fromordinal(<int>)# D/DTn from days since Christ, at midnight.<DTn>=DT.fromtimestamp(<real>)# Local time DTn from seconds since Epoch.<DTa>=DT.fromtimestamp(<real>,<tz.>)# Aware datetime from seconds since Epoch.
- ISO strings come in following forms:
'YYYY-MM-DD','HH:MM:SS.ffffff[±<offset>]', or both separated by an arbitrary character. Offset is formatted as:'HH:MM'. - Epoch on Unix systems is:
'1970-01-01 00:00 UTC','1970-01-01 01:00 CET', ...
<str>=<D/T/DT>.isoformat(sep='T')# Also timespec='auto/hours/minutes/seconds'.<str>=<D/T/DT>.strftime('<format>')# Custom string representation.<int>=<D/DT>.toordinal()# Days since Christ, ignoring time and tz.<float>=<DTn>.timestamp()# Seconds since Epoch, from DTn in local tz.<float>=<DTa>.timestamp()# Seconds since Epoch, from DTa.
>>>fromdatetimeimportdatetime>>>dt=datetime.strptime('2015-05-14 23:39:00.00 +0200','%Y-%m-%d %H:%M:%S.%f %z')>>>dt.strftime("%A, %dth of %B '%y, %I:%M%p %Z")"Thursday, 14th of May '15, 11:39PM UTC+02:00"
- When parsing,
'%z'also accepts'±HH:MM'. - For abbreviated weekday and month use
'%a'and'%b'.
<D/DT>=<D/DT> ±<TD># Returned datetime can fall into missing hour.<TD>=<D/DTn>-<D/DTn># Returns the difference, ignoring time jumps.<TD>=<DTa>-<DTa># Ignores time jumps if they share tzinfo object.<TD>=<DT_UTC>-<DT_UTC># Convert DTs to UTC to get the actual delta.
<function>(<positional_args>)# f(0, 0)<function>(<keyword_args>)# f(x=0, y=0)<function>(<positional_args>,<keyword_args>)# f(0, y=0)
deff(<nondefault_args>):# def f(x, y):deff(<default_args>):# def f(x=0, y=0):deff(<nondefault_args>,<default_args>):# def f(x, y=0):
Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.
args= (1,2)kwargs= {'x':3,'y':4,'z':5}func(*args,**kwargs)
func(1,2,x=3,y=4,z=5)
Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.
defadd(*a):returnsum(a)
>>>add(1,2,3)6
deff(x,y,z):# f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)deff(*,x,y,z):# f(x=1, y=2, z=3)deff(x,*,y,z):# f(x=1, y=2, z=3) | f(1, y=2, z=3)deff(x,y,*,z):# f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)
deff(*args):# f(1, 2, 3)deff(x,*args):# f(1, 2, 3)deff(*args,z):# f(1, 2, z=3)deff(x,*args,z):# f(1, 2, z=3)
deff(**kwargs):# f(x=1, y=2, z=3)deff(x,**kwargs):# f(x=1, y=2, z=3) | f(1, y=2, z=3)deff(*,x,**kwargs):# f(x=1, y=2, z=3)
deff(*args,**kwargs):# f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)deff(x,*args,**kwargs):# f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)deff(*args,y,**kwargs):# f(x=1, y=2, z=3) | f(1, y=2, z=3)deff(x,*args,z,**kwargs):# f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)
<list>= [*<collection> [, ...]]<set>= {*<collection> [, ...]}<tuple>= (*<collection>, [...])<dict>= {**<dict> [, ...]}
head,*body,tail=<collection>
<function>=lambda:<return_value><function>=lambda<argument_1>,<argument_2>:<return_value>
<list>= [i+1foriinrange(10)]# [1, 2, ..., 10]<set>= {iforiinrange(10)ifi>5}# {6, 7, 8, 9}<iter>= (i+5foriinrange(10))# (5, 6, ..., 14)<dict>= {i:i*2foriinrange(10)}# {0: 0, 1: 2, ..., 9: 18}
out= [i+jforiinrange(10)forjinrange(10)]
out= []foriinrange(10):forjinrange(10):out.append(i+j)
fromfunctoolsimportreduce<iter>=map(lambdax:x+1,range(10))# (1, 2, ..., 10)<iter>=filter(lambdax:x>5,range(10))# (6, 7, 8, 9)<obj>=reduce(lambdaout,x:out+x,range(10))# 45
<bool>=any(<collection>)# False if empty.<bool>=all(el[1]forelin<collection>)# True if empty.
<obj>=<expression_if_true>if<condition>else<expression_if_false>
>>> [aifaelse'zero'forain (0,1,2,3)]['zero',1,2,3]
fromcollectionsimportnamedtuplePoint=namedtuple('Point','x y')point=Point(0,0)
fromenumimportEnumDirection=Enum('Direction','n e s w')direction=Direction.n
fromdataclassesimportmake_dataclassCreature=make_dataclass('Creature', ['location','direction'])creature=Creature(Point(0,0),Direction.n)
We have a closure in Python when:
- A nested function references a value of its enclosing function and then
- the enclosing function returns the nested function.
defget_multiplier(a):defout(b):returna*breturnout
>>>multiply_by_3=get_multiplier(3)>>>multiply_by_3(10)30
- If multiple nested functions within enclosing function reference the same value, that value gets shared.
- To dynamically access function's first free variable use
'<function>.__closure__[0].cell_contents'.
fromfunctoolsimportpartial<function>=partial(<function> [,<arg_1>,<arg_2>, ...])
>>>importoperatorasop>>>multiply_by_3=partial(op.mul,3)>>>multiply_by_3(10)30
- Partial is also useful in cases when function needs to be passed as an argument, because it enables us to set its arguments beforehand.
- A few examples being:
'defaultdict(<function>)','iter(<function>, to_exclusive)'and dataclass's'field(default_factory=<function>)'.
If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.
defget_counter():i=0defout():nonlocalii+=1returnireturnout
>>>counter=get_counter()>>>counter(),counter(),counter()(1,2,3)
A decorator takes a function, adds some functionality and returns it.
@decorator_namedeffunction_that_gets_passed_to_decorator(): ...
Decorator that prints function's name every time it gets called.
fromfunctoolsimportwrapsdefdebug(func):@wraps(func)defout(*args,**kwargs):print(func.__name__)returnfunc(*args,**kwargs)returnout@debugdefadd(x,y):returnx+y
- Wraps is a helper decorator that copies the metadata of the passed function (func) to the function it is wrapping (out).
- Without it
'add.__name__'would return'out'.
Decorator that caches function's return values. All function's arguments must be hashable.
fromfunctoolsimportlru_cache@lru_cache(maxsize=None)deffib(n):returnnifn<2elsefib(n-2)+fib(n-1)
- CPython interpreter limits recursion depth to 1000 by default. To increase it use
'sys.setrecursionlimit(<depth>)'.
A decorator that accepts arguments and returns a normal decorator that accepts a function.
fromfunctoolsimportwrapsdefdebug(print_result=False):defdecorator(func):@wraps(func)defout(*args,**kwargs):result=func(*args,**kwargs)print(func.__name__,resultifprint_resultelse'')returnresultreturnoutreturndecorator@debug(print_result=True)defadd(x,y):returnx+y
class<name>:def__init__(self,a):self.a=adef__repr__(self):class_name=self.__class__.__name__returnf'{class_name}({self.a!r})'def__str__(self):returnstr(self.a)@classmethoddefget_class_name(cls):returncls.__name__
- Return value of repr() should be unambiguous and of str() readable.
- If only repr() is defined, it will also be used for str().
print(<el>)print(f'{<el>}')raiseException(<el>)loguru.logger.debug(<el>)csv.writer(<file>).writerow([<el>])
print([<el>])print(f'{<el>!r}')>>><el>loguru.logger.exception()Z=dataclasses.make_dataclass('Z', ['a']);print(Z(<el>))
class<name>:def__init__(self,a=None):self.a=a
classPerson:def__init__(self,name,age):self.name=nameself.age=ageclassEmployee(Person):def__init__(self,name,age,staff_num):super().__init__(name,age)self.staff_num=staff_num
classA:passclassB:passclassC(A,B):pass
MRO determines the order in which parent classes are traversed when searching for a method:
>>>C.mro()[<class'C'>,<class'A'>,<class'B'>,<class'object'>]
Pythonic way of implementing getters and setters.
classMyClass:@propertydefa(self):returnself._a@a.setterdefa(self,value):self._a=value
>>>el=MyClass()>>>el.a=123>>>el.a123
Decorator that automatically generates init(), repr() and eq() special methods.
fromdataclassesimportdataclass,field@dataclass(order=False,frozen=False)class<class_name>:<attr_name_1>:<type><attr_name_2>:<type>=<default_value><attr_name_3>:list/dict/set=field(default_factory=list/dict/set)
- Objects can be made sortable with
'order=True'and/or immutable and hashable with'frozen=True'. - Function field() is needed because
'<attr_name>: list = []'would make a list that is shared among all instances. - Default_factory can be anycallable.
fromdataclassesimportmake_dataclass<class>=make_dataclass('<class_name>',<coll_of_attribute_names>)<class>=make_dataclass('<class_name>',<coll_of_tuples>)<tuple>= ('<attr_name>',<type> [,<default_value>])
Mechanism that restricts objects to attributes listed in 'slots' and significantly reduces their memory footprint.
classMyClassWithSlots:__slots__= ['a']def__init__(self):self.a=1
fromcopyimportcopy,deepcopy<object>=copy(<object>)<object>=deepcopy(<object>)
A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.
- If eq() method is not overridden, it returns
'id(self) == id(other)', which is the same as'self is other'. - That means all objects compare not equal by default.
- Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted.
classMyComparable:def__init__(self,a):self.a=adef__eq__(self,other):ifisinstance(other,type(self)):returnself.a==other.areturnNotImplemented
- Hashable object needs both hash() and eq() methods and its hash value should never change.
- Hashable objects that compare equal must have the same hash value, meaning default hash() that returns
'id(self)'will not do. - That is why Python automatically makes classes unhashable if you only implement eq().
classMyHashable:def__init__(self,a):self._a=a@propertydefa(self):returnself._adef__eq__(self,other):ifisinstance(other,type(self)):returnself.a==other.areturnNotImplementeddef__hash__(self):returnhash(self.a)
- With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods.
fromfunctoolsimporttotal_ordering@total_orderingclassMySortable:def__init__(self,a):self.a=adef__eq__(self,other):ifisinstance(other,type(self)):returnself.a==other.areturnNotImplementeddef__lt__(self,other):ifisinstance(other,type(self)):returnself.a<other.areturnNotImplemented
- Any object that has methods next() and iter() is an iterator.
- Next() should return next item or raise StopIteration.
- Iter() should return 'self'.
classCounter:def__init__(self):self.i=0def__next__(self):self.i+=1returnself.idef__iter__(self):returnself
>>>counter=Counter()>>>next(counter),next(counter),next(counter)(1,2,3)
- Iterators returned by theiter() function, such as list_iterator and set_iterator.
- Objects returned by theitertools module, such as count, repeat and cycle.
- Generators returned by thegenerator functions andgenerator expressions.
- File objects returned by theopen() function, etc.
- All functions and classes have a call() method, hence are callable.
- When this cheatsheet uses
'<function>'as an argument, it actually means'<callable>'.
classCounter:def__init__(self):self.i=0def__call__(self):self.i+=1returnself.i
>>>counter=Counter()>>>counter(),counter(),counter()(1,2,3)
- Enter() should lock the resources and optionally return an object.
- Exit() should release the resources.
- Any exception that happens inside the with block is passed to the exit() method.
- If it wishes to suppress the exception it must return a true value.
classMyOpen:def__init__(self,filename):self.filename=filenamedef__enter__(self):self.file=open(self.filename)returnself.filedef__exit__(self,exc_type,exception,traceback):self.file.close()
>>>withopen('test.txt','w')asfile:...file.write('Hello World!')>>>withMyOpen('test.txt')asfile:...print(file.read())HelloWorld!
- Only required method is iter(). It should return an iterator of object's items.
- Contains() automatically works on any object that has iter() defined.
classMyIterable:def__init__(self,a):self.a=adef__iter__(self):returniter(self.a)def__contains__(self,el):returnelinself.a
>>>obj=MyIterable([1,2,3])>>> [elforelinobj][1,2,3]>>>1inobjTrue
- Only required methods are iter() and len().
- This cheatsheet actually means
'<iterable>'when it uses'<collection>'. - I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'.
classMyCollection:def__init__(self,a):self.a=adef__iter__(self):returniter(self.a)def__contains__(self,el):returnelinself.adef__len__(self):returnlen(self.a)
- Only required methods are len() and getitem().
- Getitem() should return an item at index or raise IndexError.
- Iter() and contains() automatically work on any object that has getitem() defined.
- Reversed() automatically works on any object that has getitem() and len() defined.
classMySequence:def__init__(self,a):self.a=adef__iter__(self):returniter(self.a)def__contains__(self,el):returnelinself.adef__len__(self):returnlen(self.a)def__getitem__(self,i):returnself.a[i]def__reversed__(self):returnreversed(self.a)
- It's a richer interface than the basic sequence.
- Extending it generates iter(), contains(), reversed(), index() and count().
- Unlike
'abc.Iterable'and'abc.Collection', it is not a duck type. That is why'issubclass(MySequence, abc.Sequence)'would return False even if MySequence had all the methods defined.
fromcollectionsimportabcclassMyAbcSequence(abc.Sequence):def__init__(self,a):self.a=adef__len__(self):returnlen(self.a)def__getitem__(self,i):returnself.a[i]
+------------+------------+------------+------------+--------------+| | Iterable | Collection | Sequence | abc.Sequence |+------------+------------+------------+------------+--------------+| iter() | REQ | REQ | Yes | Yes || contains() | Yes | Yes | Yes | Yes || len() | | REQ | REQ | REQ || getitem() | | | REQ | REQ || reversed() | | | Yes | Yes || index() | | | | Yes || count() | | | | Yes |+------------+------------+------------+------------+--------------+- Other ABCs that generate missing methods are: MutableSequence, Set, MutableSet, Mapping and MutableMapping.
- Names of their required methods are stored in
'<abc>.__abstractmethods__'.
fromenumimportEnum,autoclass<enum_name>(Enum):<member_name_1>=<value_1><member_name_2>=<value_2_a>,<value_2_b><member_name_3>=auto()
- If there are no numeric values before auto(), it returns 1.
- Otherwise it returns an increment of the last numeric value.
<member>=<enum>.<member_name># Returns a member.<member>=<enum>['<member_name>']# Returns a member or raises KeyError.<member>=<enum>(<value>)# Returns a member or raises ValueError.<str>=<member>.name# Returns member's name.<obj>=<member>.value# Returns member's value.
list_of_members=list(<enum>)member_names= [a.nameforain<enum>]member_values= [a.valueforain<enum>]random_member=random.choice(list(<enum>))
defget_next_member(member):members=list(member.__class__)index= (members.index(member)+1)%len(members)returnmembers[index]
Cutlery=Enum('Cutlery','fork knife spoon')Cutlery=Enum('Cutlery', ['fork','knife','spoon'])Cutlery=Enum('Cutlery', {'fork':1,'knife':2,'spoon':3})
fromfunctoolsimportpartialLogicOp=Enum('LogicOp', {'AND':partial(lambdal,r:landr),'OR' :partial(lambdal,r:lorr)})
- Another solution in this particular case is to use built-in functions and_() and or_() from the moduleoperator.
try:<code>except<exception>:<code>
try:<code_1>except<exception_a>:<code_2_a>except<exception_b>:<code_2_b>else:<code_2_c>finally:<code_3>
- Code inside the
'else'block will only be executed if'try'block had no exception. - Code inside the
'finally'block will always be executed.
except<exception>:except<exception>as<name>:except (<exception>, ...):except (<exception>, ...)as<name>:
- Also catches subclasses of the exception.
- Use
'traceback.print_exc()'to print the error message to stderr.
raise<exception>raise<exception>()raise<exception>(<el> [, ...])
except<exception>as<name>: ...raise
arguments=<name>.argsexc_type=<name>.__class__filename=<name>.__traceback__.tb_frame.f_code.co_filenamefunc_name=<name>.__traceback__.tb_frame.f_code.co_nameline=linecache.getline(filename,<name>.__traceback__.tb_lineno)error_msg=traceback.format_exception(exc_type,<name>,<name>.__traceback__)
BaseException +-- SystemExit # Raised by the sys.exit() function. +-- KeyboardInterrupt # Raised when the user hits the interrupt key (ctrl-c). +-- Exception # User-defined exceptions should be derived from this class. +-- ArithmeticError # Base class for arithmetic errors. | +-- ZeroDivisionError # Raised when dividing by zero. +-- AttributeError # Raised when an attribute is missing. +-- EOFError # Raised by input() when it hits end-of-file condition. +-- LookupError # Raised when a look-up on a collection fails. | +-- IndexError # Raised when a sequence index is out of range. | +-- KeyError # Raised when a dictionary key or set element is not found. +-- NameError # Raised when a variable name is not found. +-- OSError # Failures such as “file not found” or “disk full”. | +-- FileNotFoundError # When a file or directory is requested but doesn't exist. +-- RuntimeError # Raised by errors that don't fall into other categories. | +-- RecursionError # Raised when the maximum recursion depth is exceeded. +-- StopIteration # Raised by next() when run on an empty iterator. +-- TypeError # Raised when an argument is of wrong type. +-- ValueError # When an argument is of right type but inappropriate value. +-- UnicodeError # Raised when encoding/decoding strings to/from bytes fails.+-----------+------------+------------+------------+| | list | dict | set |+-----------+------------+------------+------------+| getitem() | IndexError | KeyError | || pop() | IndexError | KeyError | KeyError || remove() | ValueError | | KeyError || index() | ValueError | | |+-----------+------------+------------+------------+raiseTypeError('Argument is of wrong type!')raiseValueError('Argument is of right type but inappropriate value!')raiseRuntimeError('None of above!')
classMyError(Exception):passclassMyInputError(MyError):pass
Exits the interpreter by raising SystemExit exception.
importsyssys.exit()# Exits with exit code 0 (success).sys.exit(<el>)# Prints to stderr and exits with 1.sys.exit(<int>)# Exits with passed exit code.
print(<el_1>, ...,sep=' ',end='\n',file=sys.stdout,flush=False)
- Use
'file=sys.stderr'for messages about errors. - Use
'flush=True'to forcibly flush the stream.
frompprintimportpprintpprint(<collection>,width=80,depth=None,compact=False,sort_dicts=True)
- Levels deeper than 'depth' get replaced by '...'.
Reads a line from user input or pipe if present.
<str>=input(prompt=None)
- Trailing newline gets stripped.
- Prompt string is printed to the standard output before reading input.
- Raises EOFError when user hits EOF (ctrl-d/z) or input stream gets exhausted.
importsysscript_name=sys.argv[0]arguments=sys.argv[1:]
fromargparseimportArgumentParser,FileTypep=ArgumentParser(description=<str>)p.add_argument('-<short_name>','--<name>',action='store_true')# Flagp.add_argument('-<short_name>','--<name>',type=<type>)# Optionp.add_argument('<name>',type=<type>,nargs=1)# First argumentp.add_argument('<name>',type=<type>,nargs='+')# Remaining argumentsp.add_argument('<name>',type=<type>,nargs='*')# Optional argumentsargs=p.parse_args()# Exits on error.value=args.<name>
- Use
'help=<str>'to set argument description. - Use
'default=<el>'to set the default value. - Use
'type=FileType(<mode>)'for files.
Opens the file and returns a corresponding file object.
<file>=open('<path>',mode='r',encoding=None,newline=None)
'encoding=None'means that the default encoding is used, which is platform dependent. Best practice is to use'encoding="utf-8"'whenever possible.'newline=None'means all different end of line combinations are converted to '\n' on read, while on write all '\n' characters are converted to system's default line separator.'newline=""'means no conversions take place, but input is still broken into chunks by readline() and readlines() on either '\n', '\r' or '\r\n'.
'r'- Read (default).'w'- Write (truncate).'x'- Write or fail if the file already exists.'a'- Append.'w+'- Read and write (truncate).'r+'- Read and write from the start.'a+'- Read and write from the end.'t'- Text mode (default).'b'- Binary mode.
'FileNotFoundError'can be raised when reading with'r'or'r+'.'FileExistsError'can be raised when writing with'x'.'IsADirectoryError'and'PermissionError'can be raised by any.'OSError'is the parent class of all listed exceptions.
<file>.seek(0)# Moves to the start of the file.<file>.seek(offset)# Moves 'offset' chars/bytes from the start.<file>.seek(0,2)# Moves to the end of the file.<bin_file>.seek(±offset,<anchor>)# Anchor: 0 start, 1 current position, 2 end.
<str/bytes>=<file>.read(size=-1)# Reads 'size' chars/bytes or until EOF.<str/bytes>=<file>.readline()# Returns a line or empty string/bytes on EOF.<list>=<file>.readlines()# Returns a list of remaining lines.<str/bytes>=next(<file>)# Returns a line using buffer. Do not mix.
<file>.write(<str/bytes>)# Writes a string or bytes object.<file>.writelines(<collection>)# Writes a coll. of strings or bytes objects.<file>.flush()# Flushes write buffer.
- Methods do not add or strip trailing newlines, even writelines().
defread_file(filename):withopen(filename,encoding='utf-8')asfile:returnfile.readlines()
defwrite_to_file(filename,text):withopen(filename,'w',encoding='utf-8')asfile:file.write(text)
fromosimportgetcwd,path,listdirfromglobimportglob
<str>=getcwd()# Returns the current working directory.<str>=path.join(<path>, ...)# Joins two or more pathname components.<str>=path.abspath(<path>)# Returns absolute path.
<str>=path.basename(<path>)# Returns final component of the path.<str>=path.dirname(<path>)# Returns path without the final component.<tup.>=path.splitext(<path>)# Splits on last period of the final component.
<list>=listdir(path='.')# Returns filenames located at path.<list>=glob('<pattern>')# Returns paths matching the wildcard pattern.
<bool>=path.exists(<path>)# Or: <Path>.exists()<bool>=path.isfile(<path>)# Or: <DirEntry/Path>.is_file()<bool>=path.isdir(<path>)# Or: <DirEntry/Path>.is_dir()
Using scandir() instead of listdir() can significantly increase the performance of code that also needs file type information.
fromosimportscandir
<iter>=scandir(path='.')# Returns DirEntry objects located at path.<str>=<DirEntry>.path# Returns path as a string.<str>=<DirEntry>.name# Returns final component as a string.<file>=open(<DirEntry>)# Opens the file and returns file object.
frompathlibimportPath
<Path>=Path(<path> [, ...])# Accepts strings, Paths and DirEntry objects.<Path>=<path>/<path> [/ ...]# One of the paths must be a Path object.
<Path>=Path()# Returns relative cwd. Also Path('.').<Path>=Path.cwd()# Returns absolute cwd. Also Path().resolve().<Path>=<Path>.resolve()# Returns absolute Path without symlinks.
<Path>=<Path>.parent# Returns Path without final component.<str>=<Path>.name# Returns final component as a string.<str>=<Path>.stem# Returns final component without extension.<str>=<Path>.suffix# Returns final component's extension.<tup.>=<Path>.parts# Returns all components as strings.
<iter>=<Path>.iterdir()# Returns dir contents as Path objects.<iter>=<Path>.glob('<pattern>')# Returns Paths matching the wildcard pattern.
<str>=str(<Path>)# Returns path as a string.<file>=open(<Path>)# Opens the file and returns file object.
- Paths can be either strings, Paths or DirEntry objects.
- Functions report OS related errors by raising either OSError or one of itssubclasses.
importos,shutil
os.chdir(<path>)# Changes the current working directory.os.mkdir(<path>,mode=0o777)# Creates a directory. Mode is in octal.
shutil.copy(from,to)# Copies the file. 'to' can exist or be a dir.shutil.copytree(from,to)# Copies the directory. 'to' must not exist.
os.rename(from,to)# Renames/moves the file or directory.os.replace(from,to)# Same, but overwrites 'to' if it exists.
os.remove(<path>)# Deletes the file.os.rmdir(<path>)# Deletes the empty directory.shutil.rmtree(<path>)# Deletes the directory.
importos<str>=os.popen('<shell_command>').read()
>>>fromsubprocessimportrun>>>run('bc',input='1 + 1\n',capture_output=True,encoding='utf-8')CompletedProcess(args='bc',returncode=0,stdout='2\n',stderr='')
>>>fromshleximportsplit>>>os.popen('echo 1 + 1 > test.in')>>>run(split('bc -s'),stdin=open('test.in'),stdout=open('test.out','w'))CompletedProcess(args=['bc','-s'],returncode=0)>>>open('test.out').read()'2\n'
Text file format for storing collections of strings and numbers.
importjson<str>=json.dumps(<object>,ensure_ascii=True,indent=None)<object>=json.loads(<str>)
defread_json_file(filename):withopen(filename,encoding='utf-8')asfile:returnjson.load(file)
defwrite_to_json_file(filename,an_object):withopen(filename,'w',encoding='utf-8')asfile:json.dump(an_object,file,ensure_ascii=False,indent=2)
Binary file format for storing objects.
importpickle<bytes>=pickle.dumps(<object>)<object>=pickle.loads(<bytes>)
defread_pickle_file(filename):withopen(filename,'rb')asfile:returnpickle.load(file)
defwrite_to_pickle_file(filename,an_object):withopen(filename,'wb')asfile:pickle.dump(an_object,file)
Text file format for storing spreadsheets.
importcsv
<reader>=csv.reader(<file>)# Also: `dialect='excel', delimiter=','`.<list>=next(<reader>)# Returns next row as a list of strings.<list>=list(<reader>)# Returns list of remaining rows.
- File must be opened with
'newline=""'argument, or newlines embedded inside quoted fields will not be interpreted correctly!
<writer>=csv.writer(<file>)# Also: `dialect='excel', delimiter=','`.<writer>.writerow(<collection>)# Encodes objects using `str(<el>)`.<writer>.writerows(<coll_of_coll>)# Appends multiple rows.
- File must be opened with
'newline=""'argument, or '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings!
'dialect'- Master parameter that sets the default values.'delimiter'- A one-character string used to separate fields.'quotechar'- Character for quoting fields that contain special characters.'doublequote'- Whether quotechars inside fields get doubled or escaped.'skipinitialspace'- Whether whitespace after delimiter gets stripped.'lineterminator'- Specifies how writer terminates rows.'quoting'- Controls the amount of quoting: 0 - as necessary, 1 - all.'escapechar'- Character for escaping 'quotechar' if 'doublequote' is False.
+------------------+--------------+--------------+--------------+| | excel | excel-tab | unix |+------------------+--------------+--------------+--------------+| delimiter | ',' | '\t' | ',' || quotechar | '"' | '"' | '"' || doublequote | True | True | True || skipinitialspace | False | False | False || lineterminator | '\r\n' | '\r\n' | '\n' || quoting | 0 | 0 | 1 || escapechar | None | None | None |+------------------+--------------+--------------+--------------+defread_csv_file(filename):withopen(filename,encoding='utf-8',newline='')asfile:returnlist(csv.reader(file))
defwrite_to_csv_file(filename,rows):withopen(filename,'w',encoding='utf-8',newline='')asfile:writer=csv.writer(file)writer.writerows(rows)
Server-less database engine that stores each database into a separate file.
Opens a connection to the database file. Creates a new file if path doesn't exist.
importsqlite3<con>=sqlite3.connect('<path>')# Also ':memory:'.<con>.close()
Returned values can be of type str, int, float, bytes or None.
<cursor>=<con>.execute('<query>')# Can raise a subclass of sqlite3.Error.<tuple>=<cursor>.fetchone()# Returns next row. Also next(<cursor>).<list>=<cursor>.fetchall()# Returns remaining rows. Also list(<cursor>).
<con>.execute('<query>')<con>.commit()
with<con>:<con>.execute('<query>')
- Passed values can be of type str, int, float, bytes, None, bool, datetime.date or datetime.datetme.
- Bools will be stored and returned as ints and dates asISO formatted strings.
<con>.execute('<query>',<list/tuple>)# Replaces '?'s in query with values.<con>.execute('<query>',<dict/namedtuple>)# Replaces ':<key>'s with values.<con>.executemany('<query>',<coll_of_above>)# Runs execute() many times.
In this example values are not actually saved because'con.commit()' is omitted!
>>>con=sqlite3.connect('test.db')>>>con.execute('create table person (person_id integer primary key, name, height)')>>>con.execute('insert into person values (null, ?, ?)', ('Jean-Luc',187)).lastrowid1>>>con.execute('select * from person').fetchall()[(1,'Jean-Luc',187)]
Has a very similar interface, with differences listed below.
# $ pip3 install mysql-connectorfrommysqlimportconnector<con>=connector.connect(host=<str>, …)# `user=<str>, password=<str>, database=<str>`.<cursor>=<con>.cursor()# Only cursor has execute method.<cursor>.execute('<query>')# Can raise a subclass of connector.Error.<cursor>.execute('<query>',<list/tuple>)# Replaces '%s's in query with values.<cursor>.execute('<query>',<dict/namedtuple>)# Replaces '%(<key>)s's with values.
Bytes object is an immutable sequence of single bytes. Mutable version is called bytearray.
<bytes>=b'<str>'# Only accepts ASCII characters and \x00 - \xff.<int>=<bytes>[<index>]# Returns int in range from 0 to 255.<bytes>=<bytes>[<slice>]# Returns bytes even if it has only one element.<bytes>=<bytes>.join(<coll_of_bytes>)# Joins elements using bytes object as separator.
<bytes>=bytes(<coll_of_ints>)# Ints must be in range from 0 to 255.<bytes>=bytes(<str>,'utf-8')# Or: <str>.encode('utf-8')<bytes>=<int>.to_bytes(n_bytes, …)# `byteorder='big/little', signed=False`.<bytes>=bytes.fromhex('<hex>')# Hex numbers can be separated by spaces.
<list>=list(<bytes>)# Returns ints in range from 0 to 255.<str>=str(<bytes>,'utf-8')# Or: <bytes>.decode('utf-8')<int>=int.from_bytes(<bytes>, …)# `byteorder='big/little', signed=False`.'<hex>'=<bytes>.hex()# Returns a string of hexadecimal numbers.
defread_bytes(filename):withopen(filename,'rb')asfile:returnfile.read()
defwrite_bytes(filename,bytes_obj):withopen(filename,'wb')asfile:file.write(bytes_obj)
- Module that performs conversions between a sequence of numbers and a bytes object.
- Machine’s native type sizes and byte order are used by default.
fromstructimportpack,unpack,iter_unpack<bytes>=pack('<format>',<num_1> [,<num_2>, ...])<tuple>=unpack('<format>',<bytes>)<tuples>=iter_unpack('<format>',<bytes>)
>>>pack('>hhl',1,2,3)b'\x00\x01\x00\x02\x00\x00\x00\x03'>>>unpack('>hhl',b'\x00\x01\x00\x02\x00\x00\x00\x03')(1,2,3)
'='- native byte order'<'- little-endian'>'- big-endian (also'!')
'x'- pad byte'b'- char (1)'h'- short (2)'i'- int (4)'l'- long (4)'q'- long long (8)
'f'- float (4)'d'- double (8)
List that can only hold numbers of a predefined type. Available types and their sizes in bytes are listed above.
fromarrayimportarray<array>=array('<typecode>',<collection>)# Array from collection of numbers.<array>=array('<typecode>',<bytes>)# Array from bytes object.<array>=array('<typecode>',<array>)# Treats array as a sequence of numbers.<bytes>=bytes(<array>)# Or: <array>.tobytes()
- A sequence object that points to the memory of another object.
- Each element can reference a single or multiple consecutive bytes, depending on format.
- Order and number of elements can be changed with slicing.
<mview>=memoryview(<bytes/bytearray/array>)# Immutable if bytes, else mutable.<real>=<mview>[<index>]# Returns an int or a float.<mview>=<mview>[<slice>]# Mview with rearranged elements.<mview>=<mview>.cast('<typecode>')# Casts memoryview to the new format.<mview>.release()# Releases the object's memory buffer.
<bin_file>.write(<mview>)# Writes mview to the binary file.<bytes>=bytes(<mview>)# Creates a new bytes object.<bytes>=<bytes>.join(<coll_of_mviews>)# Joins mviews using bytes object as sep.<array>=array('<typecode>',<mview>)# Treats mview as a sequence of numbers.
<list>=list(<mview>)# Returns list of ints or floats.<str>=str(<mview>,'utf-8')# Treats mview as a bytes object.<int>=int.from_bytes(<mview>, …)# `byteorder='big/little', signed=False`.'<hex>'=<mview>.hex()# Treats mview as a bytes object.
A thread-safe list with efficient appends and pops from either side. Pronounced "deck".
fromcollectionsimportdeque<deque>=deque(<collection>,maxlen=None)
<deque>.appendleft(<el>)# Opposite element is dropped if full.<deque>.extendleft(<collection>)# Collection gets reversed.<el>=<deque>.popleft()# Raises IndexError if empty.<deque>.rotate(n=1)# Rotates elements to the right.
- CPython interpreter can only run a single thread at a time.
- That is why using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.
fromthreadingimportThread,RLock,Semaphore,Event,Barrier
<Thread>=Thread(target=<function>)# Use `args=<collection>` to set arguments.<Thread>.start()# Starts the thread.<bool>=<Thread>.is_alive()# Checks if thread has finished executing.<Thread>.join()# Waits for thread to finish.
- Use
'kwargs=<dict>'to pass keyword arguments to the function. - Use
'daemon=True', or the program will not be able to exit while the thread is alive.
<lock>=RLock()<lock>.acquire()# Waits for lock to be available.<lock>.release()# Makes the lock available again.
lock=RLock()withlock: ...
<Semaphore>=Semaphore(value=1)# Lock that can be acquired 'value' times.<Event>=Event()# Method wait() blocks until set() is called.<Barrier>=Barrier(n_times)# Method wait() blocks until it's called 'n_times'.
fromconcurrent.futuresimportThreadPoolExecutorwithThreadPoolExecutor(max_workers=None)asexecutor:# Does not exit until done.<iter>=executor.map(lambdax:x+1,range(3))# (1, 2, 3)<iter>=executor.map(lambdax,y:x+y,'abc','123')# ('a1', 'b2', 'c3')<Future>=executor.submit(<function> [,<arg_1>, ...])# Also visible outside block.
<bool>=<Future>.done()# Checks if thread has finished executing.<obj>=<Future>.result()# Waits for thread to finish and returns result.
A thread-safe FIFO queue. For LIFO queue use LifoQueue.
fromqueueimportQueue<Queue>=Queue(maxsize=0)
<Queue>.put(<el>)# Blocks until queue stops being full.<Queue>.put_nowait(<el>)# Raises queue.Full exception if full.<el>=<Queue>.get()# Blocks until queue stops being empty.<el>=<Queue>.get_nowait()# Raises queue.Empty exception if empty.
Module of functions that provide the functionality of operators.
fromoperatorimportadd,sub,mul,truediv,floordiv,mod,pow,neg,absfromoperatorimporteq,ne,lt,le,gt,gefromoperatorimportand_,or_,not_fromoperatorimportitemgetter,attrgetter,methodcaller
importoperatorasopelementwise_sum=map(op.add,list_a,list_b)sorted_by_second=sorted(<collection>,key=op.itemgetter(1))sorted_by_both=sorted(<collection>,key=op.itemgetter(1,0))product_of_elems=functools.reduce(op.mul,<collection>)LogicOp=enum.Enum('LogicOp', {'AND':op.and_,'OR' :op.or_})last_el=op.methodcaller('pop')(<list>)
Inspecting code at runtime.
<list>=dir()# Names of local variables (incl. functions).<dict>=vars()# Dict of local variables. Also locals().<dict>=globals()# Dict of global variables.
<list>=dir(<object>)# Names of object's attributes (incl. methods).<dict>=vars(<object>)# Dict of object's fields. Also <obj>.__dict__.<bool>=hasattr(<object>,'<attr_name>')# Checks if getattr() raises an error.value=getattr(<object>,'<attr_name>')# Raises AttributeError if attribute is missing.setattr(<object>,'<attr_name>',value)# Only works on objects with __dict__ attribute.delattr(<object>,'<attr_name>')# Equivalent to `del <object>.<attr_name>`.
frominspectimportsignature<sig>=signature(<function>)no_of_params=len(<sig>.parameters)param_names=list(<sig>.parameters.keys())param_kinds= [a.kindforain<sig>.parameters.values()]
Code that generates code.
Type is the root class. If only passed an object it returns its type (class). Otherwise it creates a new class.
<class>=type('<class_name>',<parents_tuple>,<attributes_dict>)
>>>Z=type('Z', (), {'a':'abcde','b':12345})>>>z=Z()
A class that creates classes.
defmy_meta_class(name,parents,attrs):attrs['a']='abcde'returntype(name,parents,attrs)
classMyMetaClass(type):def__new__(cls,name,parents,attrs):attrs['a']='abcde'returntype.__new__(cls,name,parents,attrs)
- New() is a class method that gets called before init(). If it returns an instance of its class, then that instance gets passed to init() as a 'self' argument.
- It receives the same arguments as init(), except for the first one that specifies the desired type of the returned instance (MyMetaClass in our case).
- Like in our case, new() can also be called directly, usually from a new() method of a child class (
def __new__(cls): return super().__new__(cls)). - The only difference between the examples above is that my_meta_class() returns a class of type type, while MyMetaClass() returns a class of type MyMetaClass.
Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of his parents has it defined and eventually comes to type().
classMyClass(metaclass=MyMetaClass):b=12345
>>>MyClass.a,MyClass.b('abcde',12345)
type(MyClass)==MyMetaClass# MyClass is an instance of MyMetaClass.type(MyMetaClass)==type# MyMetaClass is an instance of type.
+-------------+-------------+| Classes | Metaclasses |+-------------+-------------|| MyClass --> MyMetaClass || | v || object -----> type <+ || | ^ +--+ || str ----------+ |+-------------+-------------+MyClass.__base__==object# MyClass is a subclass of object.MyMetaClass.__base__==type# MyMetaClass is a subclass of type.
+-------------+-------------+| Classes | Metaclasses |+-------------+-------------|| MyClass | MyMetaClass || v | v || object <----- type || ^ | || str | |+-------------+-------------+>>>fromastimportliteral_eval>>>literal_eval('1 + 2')3>>>literal_eval('[1, 2, 3]')[1,2,3]>>>literal_eval('abs(1)')ValueError:malformednodeorstring
- Coroutines have a lot in common with threads, but unlike threads, they only give up control when they call another coroutine and they don’t use as much memory.
- Coroutine definition starts with
'async'and its call with'await'. 'asyncio.run(<coroutine>)'is the main entry point for asynchronous programs.- Functions wait(), gather() and as_completed() can be used when multiple coroutines need to be started at the same time.
- Asyncio module also provides its ownQueue,Event,Lock andSemaphore classes.
importasyncio,collections,curses,enum,randomP=collections.namedtuple('P','x y')# PositionD=enum.Enum('D','n e s w')# Directiondefmain(screen):curses.curs_set(0)# Makes cursor invisible.screen.nodelay(True)# Makes getch() non-blocking.asyncio.run(main_coroutine(screen))# Starts running asyncio code.asyncdefmain_coroutine(screen):state= {'*':P(0,0),**{id_:P(30,10)forid_inrange(10)}}moves=asyncio.Queue()coros= (*(random_controller(id_,moves)forid_inrange(10)),human_controller(screen,moves),model(moves,state,*screen.getmaxyx()),view(state,screen))awaitasyncio.wait(coros,return_when=asyncio.FIRST_COMPLETED)asyncdefrandom_controller(id_,moves):whileTrue:moves.put_nowait((id_,random.choice(list(D))))awaitasyncio.sleep(random.random()/2)asyncdefhuman_controller(screen,moves):whileTrue:ch=screen.getch()key_mappings= {259:D.n,261:D.e,258:D.s,260:D.w}ifchinkey_mappings:moves.put_nowait(('*',key_mappings[ch]))awaitasyncio.sleep(0.01)asyncdefmodel(moves,state,height,width):whilestate['*']notin {pforid_,pinstate.items()ifid_!='*'}:id_,d=awaitmoves.get()p=state[id_]deltas= {D.n:P(0,-1),D.e:P(1,0),D.s:P(0,1),D.w:P(-1,0)}new_p=P(*[sum(a)forainzip(p,deltas[d])])if0<=new_p.x<width-1and0<=new_p.y<height:state[id_]=new_pasyncdefview(state,screen):whileTrue:screen.clear()forid_,pinstate.items():screen.addstr(p.y,p.x,str(id_))awaitasyncio.sleep(0.01)curses.wrapper(main)
# $ pip3 install tqdmfromtqdmimporttqdmfromtimeimportsleepforelintqdm([1,2,3]):sleep(0.2)
# $ pip3 install matplotlibfrommatplotlibimportpyplotpyplot.plot(<y_data> [,label=<str>])pyplot.plot(<x_data>,<y_data>)pyplot.legend()# Adds a legend.pyplot.savefig('<path>')# Saves the figure.pyplot.show()# Displays the figure.pyplot.clf()# Clears the figure.
# $ pip3 install tabulateimportcsv,tabulatewithopen('test.csv',encoding='utf-8',newline='')asfile:rows=csv.reader(file)header= [a.title()forainnext(rows)]table=tabulate.tabulate(rows,header)print(table)
fromcursesimportwrapper,curs_set,asciifromcursesimportKEY_UP,KEY_RIGHT,KEY_DOWN,KEY_LEFTdefmain():wrapper(draw)defdraw(screen):curs_set(0)# Makes cursor invisible.screen.nodelay(True)# Makes getch() non-blocking.screen.clear()screen.addstr(0,0,'Press ESC to quit.')# Coordinates are y, x.whilescreen.getch()!=ascii.ESC:passdefget_border(screen):fromcollectionsimportnamedtupleP=namedtuple('P','x y')height,width=screen.getmaxyx()returnP(width-1,height-1)if__name__=='__main__':main()
# $ pip3 install logurufromloguruimportlogger
logger.add('debug_{time}.log',colorize=True)# Connects a log file.logger.add('error_{time}.log',level='ERROR')# Another file for errors or higher.logger.<level>('A logging message.')
- Levels:
'debug','info','success','warning','error','critical'.
Exception description, stack trace and values of variables are appended automatically.
try: ...except<exception>:logger.exception('An error happened.')
Argument that sets a condition when a new log file is created.
rotation=<int>|<datetime.timedelta>|<datetime.time>|<str>
'<int>'- Max file size in bytes.'<timedelta>'- Max age of a file.'<time>'- Time of day.'<str>'- Any of above as a string:'100 MB','1 month','monday at 12:00', ...
Sets a condition which old log files get deleted.
retention=<int>|<datetime.timedelta>|<str>
'<int>'- Max number of files.'<timedelta>'- Max age of a file.'<str>'- Max age as a string:'1 week, 3 days','2 months', ...
# $ pip3 install requests beautifulsoup4importrequests,sysfrombs4importBeautifulSoupURL='https://en.wikipedia.org/wiki/Python_(programming_language)'try:html=requests.get(URL).textdoc=BeautifulSoup(html,'html.parser')table=doc.find('table',class_='infobox vevent')rows=table.find_all('tr')link=rows[11].find('a')['href']ver=rows[6].find('div').text.split()[0]url_i=rows[0].find('img')['src']image=requests.get(f'https:{url_i}').contentwithopen('test.png','wb')asfile:file.write(image)print(link,ver)exceptrequests.exceptions.ConnectionError:print("You've got problems with connection.",file=sys.stderr)
# $ pip3 install bottlefrombottleimportrun,route,static_file,template,post,request,responseimportjson
run(host='localhost',port=8080)# Runs locally.run(host='0.0.0.0',port=80)# Runs globally.
@route('/img/<image>')defsend_image(image):returnstatic_file(image,'img_dir/',mimetype='image/png')
@route('/<sport>')defsend_page(sport):returntemplate('<h1>{{title}}</h1>',title=sport)
@post('/odds/<sport>')defodds_handler(sport):team=request.forms.get('team')home_odds,away_odds=2.44,3.29response.headers['Content-Type']='application/json'response.headers['Cache-Control']='no-cache'returnjson.dumps([team,home_odds,away_odds])
# $ pip3 install requests>>>importrequests>>>url='http://localhost:8080/odds/football'>>>data= {'team':'arsenal f.c.'}>>>response=requests.post(url,data=data)>>>response.json()['arsenal f.c.',2.44,3.29]
fromtimeimporttimestart_time=time()# Seconds since the Epoch....duration=time()-start_time
fromtimeimportperf_counterstart_time=perf_counter()# Seconds since restart....duration=perf_counter()-start_time
>>>fromtimeitimporttimeit>>>timeit('"-".join(str(i) for i in range(100))',...number=10000,globals=globals(),setup='pass')0.34986
# $ pip3 install line_profiler memory_profiler@profiledefmain():a= [*range(10000)]b= {*range(10000)}main()
$ kernprof -lv test.pyLine # Hits Time Per Hit % Time Line Contents======================================================= 1 @profile 2 def main(): 3 1 1128.0 1128.0 27.4 a = [*range(10000)] 4 1 2994.0 2994.0 72.6 b = {*range(10000)}$ python3 -m memory_profiler test.pyLine # Mem usage Increment Line Contents======================================================= 1 35.387 MiB 35.387 MiB @profile 2 def main(): 3 35.734 MiB 0.348 MiB a = [*range(10000)] 4 36.160 MiB 0.426 MiB b = {*range(10000)}# $ pip3 install pycallgraphfrompycallgraphimportoutput,PyCallGraphfromdatetimeimportdatetimetime_str=datetime.now().strftime('%Y%m%d%H%M%S')filename=f'profile-{time_str}.png'drawer=output.GraphvizOutput(output_file=filename)withPyCallGraph(drawer):<code_to_be_profiled>
Array manipulation mini-language. It can run up to one hundred times faster than the equivalent Python code. An even faster alternative that runs on a GPU is called CuPy.
# $ pip3 install numpyimportnumpyasnp
<array>=np.array(<list>)<array>=np.arange(from_inclusive,to_exclusive, ±step_size)<array>=np.ones(<shape>)<array>=np.random.randint(from_inclusive,to_exclusive,<shape>)
<array>.shape=<shape><view>=<array>.reshape(<shape>)<view>=np.broadcast_to(<array>,<shape>)
<array>=<array>.sum(axis)indexes=<array>.argmin(axis)
- Shape is a tuple of dimension sizes.
- Axis is the index of a dimension that gets collapsed. The leftmost dimension has index 0.
<el> =<2d_array>[0, 0]# First element.<1d_view> =<2d_array>[0]# First row.<1d_view> =<2d_array>[:, 0]# First column. Also [..., 0].<3d_view> =<2d_array>[None, :, :]# Expanded by dimension of size 1.
<1d_array> =<2d_array>[<1d_row_indexes>,<1d_column_indexes>]<2d_array> =<2d_array>[<2d_row_indexes>,<2d_column_indexes>]
<2d_bools> =<2d_array>> 0<1d_array> =<2d_array>[<2d_bools>]
- If row and column indexes differ in shape, they are combined with broadcasting.
Broadcasting is a set of rules by which NumPy functions operate on arrays of different sizes and/or dimensions.
left= [[0.1], [0.6], [0.8]]# Shape: (3, 1)right= [0.1 ,0.6 ,0.8 ]# Shape: (3)
left= [[0.1], [0.6], [0.8]]# Shape: (3, 1)right= [[0.1 ,0.6 ,0.8]]# Shape: (1, 3) <- !
2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:
left= [[0.1,0.1,0.1], [0.6,0.6,0.6], [0.8,0.8,0.8]]# Shape: (3, 3) <- !right= [[0.1,0.6,0.8], [0.1,0.6,0.8], [0.1,0.6,0.8]]# Shape: (3, 3) <- !
>>>points=np.array([0.1,0.6,0.8]) [0.1,0.6,0.8]>>>wrapped_points=points.reshape(3,1)[[0.1], [0.6], [0.8]]>>>distances=wrapped_points-points[[0. ,-0.5,-0.7], [0.5,0. ,-0.2], [0.7,0.2,0. ]]>>>distances=np.abs(distances)[[0. ,0.5,0.7], [0.5,0. ,0.2], [0.7,0.2,0. ]]>>>i=np.arange(3)[0,1,2]>>>distances[i,i]=np.inf[[inf,0.5,0.7], [0.5,inf,0.2], [0.7,0.2,inf]]>>>distances.argmin(1)[1,2,1]
# $ pip3 install pillowfromPILimportImage
<Image>=Image.new('<mode>', (width,height))<Image>=Image.open('<path>')<Image>=<Image>.convert('<mode>')<Image>.save('<path>')<Image>.show()
<int/tuple>=<Image>.getpixel((x,y))# Returns a pixel.<Image>.putpixel((x,y),<int/tuple>)# Writes a pixel to the image.<ImagingCore>=<Image>.getdata()# Returns a sequence of pixels.<Image>.putdata(<list/ImagingCore>)# Writes a sequence of pixels.<Image>.paste(<Image>, (x,y))# Writes an image to the image.
<2d_array> = np.array(<Image_L>)# Creates NumPy array from greyscale image.<3d_array> = np.array(<Image_RGB>)# Creates NumPy array from color image.<Image> = Image.fromarray(<array>)# Creates image from NumPy array of floats.
'1'- 1-bit pixels, black and white, stored with one pixel per byte.'L'- 8-bit pixels, greyscale.'RGB'- 3x8-bit pixels, true color.'RGBA'- 4x8-bit pixels, true color with transparency mask.'HSV'- 3x8-bit pixels, Hue, Saturation, Value color space.
WIDTH,HEIGHT=100,100size=WIDTH*HEIGHThues= [255*i/sizeforiinrange(size)]img=Image.new('HSV', (WIDTH,HEIGHT))img.putdata([(int(h),255,255)forhinhues])img.convert('RGB').save('test.png')
fromrandomimportrandintadd_noise=lambdavalue:max(0,min(255,value+randint(-20,20)))img=Image.open('test.png').convert('HSV')img.putdata([(add_noise(h),s,v)forh,s,vinimg.getdata()])img.convert('RGB').save('test.png')
fromPILimportImageDraw
<ImageDraw>=ImageDraw.Draw(<Image>)<ImageDraw>.point((x,y),fill=None)<ImageDraw>.line((x1,y1,x2,y2 [, ...]),fill=None,width=0,joint=None)<ImageDraw>.arc((x1,y1,x2,y2),from_deg,to_deg,fill=None,width=0)<ImageDraw>.rectangle((x1,y1,x2,y2),fill=None,outline=None,width=0)<ImageDraw>.polygon((x1,y1,x2,y2 [, ...]),fill=None,outline=None)<ImageDraw>.ellipse((x1,y1,x2,y2),fill=None,outline=None,width=0)
- Use
'fill=<color>'to set the primary color. - Use
'outline=<color>'to set the secondary color. - Color can be specified as a tuple, int,
'#rrggbb'string or a color name.
# $ pip3 install pillow imageiofromPILimportImage,ImageDrawimportimageioWIDTH,R=126,10frames= []forvelocityinrange(15):y=sum(range(velocity+1))frame=Image.new('L', (WIDTH,WIDTH))draw=ImageDraw.Draw(frame)draw.ellipse((WIDTH/2-R,y,WIDTH/2+R,y+R*2),fill='white')frames.append(frame)frames+=reversed(frames[1:-1])imageio.mimsave('test.gif',frames,duration=0.03)
importwave
<Wave_read>=wave.open('<path>','rb')# Opens the WAV file.framerate=<Wave_read>.getframerate()# Number of frames per second.nchannels=<Wave_read>.getnchannels()# Number of samples per frame.sampwidth=<Wave_read>.getsampwidth()# Sample size in bytes.nframes=<Wave_read>.getnframes()# Number of frames.<params>=<Wave_read>.getparams()# Immutable collection of above.<bytes>=<Wave_read>.readframes(nframes)# Returns next 'nframes' frames.
<Wave_write>=wave.open('<path>','wb')# Truncates existing file.<Wave_write>.setframerate(<int>)# 44100 for CD, 48000 for video.<Wave_write>.setnchannels(<int>)# 1 for mono, 2 for stereo.<Wave_write>.setsampwidth(<int>)# 2 for CD quality sound.<Wave_write>.setparams(<params>)# Sets all parameters.<Wave_write>.writeframes(<bytes>)# Appends frames to the file.
- Bytes object contains a sequence of frames, each consisting of one or more samples.
- In a stereo signal, the first sample of a frame belongs to the left channel.
- Each sample consists of one or more bytes that, when converted to an integer, indicate the displacement of a speaker membrane at a given moment.
- If sample width is one, then the integer should be encoded unsigned.
- For all other sizes, the integer should be encoded signed with little-endian byte order.
+-----------+-------------+------+-------------+| sampwidth | min | zero | max |+-----------+-------------+------+-------------+| 1 | 0 | 128 | 255 || 2 | -32768 | 0 | 32767 || 3 | -8388608 | 0 | 8388607 || 4 | -2147483648 | 0 | 2147483647 |+-----------+-------------+------+-------------+defread_wav_file(filename):defget_int(a_bytes):an_int=int.from_bytes(a_bytes,'little',signed=width!=1)returnan_int-128* (width==1)withwave.open(filename,'rb')asfile:width=file.getsampwidth()frames=file.readframes(-1)byte_samples= (frames[i:i+width]foriinrange(0,len(frames),width))return [get_int(b)/pow(2,width*8-1)forbinbyte_samples]
defwrite_to_wav_file(filename,float_samples,nchannels=1,sampwidth=2,framerate=44100):defget_bytes(a_float):a_float=max(-1,min(1-2e-16,a_float))a_float+=sampwidth==1a_float*=pow(2,sampwidth*8-1)returnint(a_float).to_bytes(sampwidth,'little',signed=sampwidth!=1)withwave.open(filename,'wb')asfile:file.setnchannels(nchannels)file.setsampwidth(sampwidth)file.setframerate(framerate)file.writeframes(b''.join(get_bytes(f)forfinfloat_samples))
frommathimportpi,sinsamples_f= (sin(i*2*pi*440/44100)foriinrange(100000))write_to_wav_file('test.wav',samples_f)
fromrandomimportrandomadd_noise=lambdavalue:value+ (random()-0.5)*0.03samples_f= (add_noise(f)forfinread_wav_file('test.wav'))write_to_wav_file('test.wav',samples_f)
# $ pip3 install simpleaudiofromsimpleaudioimportplay_bufferwithwave.open('test.wav','rb')asfile:p=file.getparams()frames=file.readframes(-1)play_buffer(frames,p.nchannels,p.sampwidth,p.framerate)
# $ pip3 install pyttsx3importpyttsx3engine=pyttsx3.init()engine.say('Sally sells seashells by the seashore.')engine.runAndWait()
# $ pip3 install simpleaudioimportsimpleaudio,math,structfromitertoolsimportchain,repeatF=44100P1='71♪,69,,71♪,66,,62♪,66,,59♪,,,'P2='71♪,73,,74♪,73,,74,,71,,73♪,71,,73,,69,,71♪,69,,71,,67,,71♪,,,'get_pause=lambdaseconds:repeat(0,int(seconds*F))sin_f=lambdai,hz:math.sin(i*2*math.pi*hz/F)get_wave=lambdahz,seconds: (sin_f(i,hz)foriinrange(int(seconds*F)))get_hz=lambdakey:8.176*2** (int(key)/12)parse_note=lambdanote: (get_hz(note[:2]),0.25if'♪'innoteelse0.125)get_samples=lambdanote:get_wave(*parse_note(note))ifnoteelseget_pause(0.125)samples_f=chain.from_iterable(get_samples(n)forninf'{P1}{P1}{P2}'.split(','))samples_b=b''.join(struct.pack('<h',int(f*30000))forfinsamples_f)simpleaudio.play_buffer(samples_b,1,2,F)
# $ pip3 install pygameimportpygameaspgpg.init()screen=pg.display.set_mode((500,500))rect=pg.Rect(240,240,20,20)whileall(event.type!=pg.QUITforeventinpg.event.get()):deltas= {pg.K_UP: (0,-3),pg.K_RIGHT: (3,0),pg.K_DOWN: (0,3),pg.K_LEFT: (-3,0)}fordeltain (deltas.get(i)fori,oninenumerate(pg.key.get_pressed())ifon):rect=rect.move(delta)ifdeltaelserectscreen.fill((0,0,0))pg.draw.rect(screen, (255,255,255),rect)pg.display.flip()
Object for storing rectangular coordinates.
<Rect>=pg.Rect(x,y,width,height)# X and y are coordinates of topleft corner.<int>=<Rect>.x/y/centerx/centery/…# Top, right, bottom, left.<tup.>=<Rect>.topleft/center/…# Topright, bottomright, bottomleft.<Rect>=<Rect>.move((x,y))# Use move_ip() to move in place.
<bool>=<Rect>.collidepoint((x,y))# Tests if a point is inside the rectangle.<bool>=<Rect>.colliderect(<Rect>)# Tests if two rectangles overlap.<int>=<Rect>.collidelist(<list_of_Rect>)# Returns index of first colliding Rect or -1.<list>=<Rect>.collidelistall(<list_of_Rect>)# Returns indexes of all colliding Rects.
Object for representing images.
<Surf>=pg.display.set_mode((width,height))# Returns the display surface.<Surf>=pg.Surface((width,height))# Creates a new surface.<Surf>=pg.image.load('<path>')# Loads the image.<Surf>=<Surf>.subsurface(<Rect>)# Returns a subsurface.
<Surf>.fill(color)# Fills the whole surface.<Surf>.set_at((x,y),color)# Updates pixel.<Surf>.blit(<Surface>, (x,y))# Draws passed surface to the surface.
<Surf>=pg.transform.flip(<Surf>,xbool,ybool)<Surf>=pg.transform.rotate(<Surf>,degrees)<Surf>=pg.transform.scale(<Surf>, (width,height))
pg.draw.line(<Surf>,color, (x1,y1), (x2,y2),width)pg.draw.arc(<Surf>,color,<Rect>,from_radians,to_radians)pg.draw.rect(<Surf>,color,<Rect>)pg.draw.polygon(<Surf>,color,points)pg.draw.ellipse(<Surf>,color,<Rect>)
<Font>=pg.font.SysFont('<name>',size,bold=False,italic=False)<Font>=pg.font.Font('<path>',size)<Surf>=<Font>.render(text,antialias,color [,background])
<Sound>=pg.mixer.Sound('<path>')# Loads the WAV file.<Sound>.play()# Starts playing the sound.
importcollections,dataclasses,enum,io,pygame,urllib.request,itertoolsasitfromrandomimportrandintP=collections.namedtuple('P','x y')# PositionD=enum.Enum('D','n e s w')# DirectionSIZE,MAX_SPEED=50,P(5,10)# Screen size, Speed limitdefmain():defget_screen():pygame.init()returnpygame.display.set_mode(2* [SIZE*16])defget_images():url='https://gto76.github.io/python-cheatsheet/web/mario_bros.png'img=pygame.image.load(io.BytesIO(urllib.request.urlopen(url).read()))return [img.subsurface(get_rect(x,0))forxinrange(img.get_width()//16)]defget_mario():Mario=dataclasses.make_dataclass('Mario','rect spd facing_left frame_cycle'.split())returnMario(get_rect(1,1),P(0,0),False,it.cycle(range(3)))defget_tiles():positions= [pforpinit.product(range(SIZE),repeat=2)if {*p}& {0,SIZE-1}]+ \ [(randint(1,SIZE-2),randint(2,SIZE-2))for_inrange(SIZE**2//10)]return [get_rect(*p)forpinpositions]defget_rect(x,y):returnpygame.Rect(x*16,y*16,16,16)run(get_screen(),get_images(),get_mario(),get_tiles())defrun(screen,images,mario,tiles):clock=pygame.time.Clock()whileall(event.type!=pygame.QUITforeventinpygame.event.get()):keys= {pygame.K_UP:D.n,pygame.K_RIGHT:D.e,pygame.K_DOWN:D.s,pygame.K_LEFT:D.w}pressed= {keys.get(i)fori,oninenumerate(pygame.key.get_pressed())ifon}update_speed(mario,tiles,pressed)update_position(mario,tiles)draw(screen,images,mario,tiles,pressed)clock.tick(28)defupdate_speed(mario,tiles,pressed):x,y=mario.spdx+=2* ((D.einpressed)- (D.winpressed))x-=x//abs(x)ifxelse0y+=1ifD.snotinget_boundaries(mario.rect,tiles)else (D.ninpressed)*-10mario.spd=P(*[max(-limit,min(limit,s))forlimit,sinzip(MAX_SPEED,P(x,y))])defupdate_position(mario,tiles):new_p=mario.rect.topleftlarger_speed=max(abs(s)forsinmario.spd)for_inrange(larger_speed):mario.spd=stop_on_collision(mario.spd,get_boundaries(mario.rect,tiles))new_p=P(*[a+s/larger_speedfora,sinzip(new_p,mario.spd)])mario.rect.topleft=new_pdefget_boundaries(rect,tiles):deltas= {D.n:P(0,-1),D.e:P(1,0),D.s:P(0,1),D.w:P(-1,0)}return {dford,deltaindeltas.items()ifrect.move(delta).collidelist(tiles)!=-1}defstop_on_collision(spd,bounds):returnP(x=0if (D.winboundsandspd.x<0)or (D.einboundsandspd.x>0)elsespd.x,y=0if (D.ninboundsandspd.y<0)or (D.sinboundsandspd.y>0)elsespd.y)defdraw(screen,images,mario,tiles,pressed):defget_frame_index():ifD.snotinget_boundaries(mario.rect,tiles):return4returnnext(mario.frame_cycle)if {D.w,D.e}&pressedelse6screen.fill((85,168,255))mario.facing_left= (D.winpressed)if {D.w,D.e}&pressedelsemario.facing_leftscreen.blit(images[get_frame_index()+mario.facing_left*9],mario.rect)forrectintiles:screen.blit(images[18if {*rect.topleft}& {0, (SIZE-1)*16}else19],rect)pygame.display.flip()if__name__=='__main__':main()
# $ pip3 install pandasimportpandasaspdfrompandasimportSeries,DataFrame
Ordered dictionary with a name.
>>>Series([1,2],index=['x','y'],name='a')x1y2Name:a,dtype:int64
<Sr>=Series(<list>)# Assigns RangeIndex starting at 0.<Sr>=Series(<dict>)# Takes dictionary's keys for index.<Sr>=Series(<dict/Series>,index=<list>)# Only keeps items with keys specified in index.
<el>=<Sr>.loc[key]# Or: <Sr>.iloc[index]<Sr>=<Sr>.loc[keys]# Or: <Sr>.iloc[indexes]<Sr>=<Sr>.loc[from_key :to_key_inclusive]# Or: <Sr>.iloc[from_i : to_i_exclusive]
<el>=<Sr>[key/index]# Or: <Sr>.key<Sr>=<Sr>[keys/indexes]# Or: <Sr>[<key_range/range>]<Sr>=<Sr>[bools]# Or: <Sr>.i/loc[bools]
<Sr>=<Sr>><==<el/Sr># Returns a Series of bools.<Sr>=<Sr>+-*/<el/Sr># Non-matching keys get value NaN.
<Sr>=<Sr>.append(<Sr>)# Or: pd.concat(<coll_of_Sr>)<Sr>=<Sr>.combine_first(<Sr>)# Adds items that are not yet present.<Sr>.update(<Sr>)# Updates items that are already present.
<el>=<Sr>.sum/max/mean/idxmax/all()# Or: <Sr>.aggregate(<agg_func>)<Sr>=<Sr>.rank/diff/cumsum/ffill/interpl()# Or: <Sr>.agg/transform(<trans_func>)<Sr>=<Sr>.fillna(<el>)# Or: <Sr>.apply/agg/transform/map(<map_func>)
- The way
'aggregate()'and'transform()'find out whether the passed function accepts an element or the whole Series is by passing it a single value at first and if it raises an error, then they pass it the whole Series.
>>>sr=Series([1,2],index=['x','y'])x1y2
+-------------+-------------+-------------+---------------+| | 'sum' | ['sum'] | {'s': 'sum'} |+-------------+-------------+-------------+---------------+| sr.apply(…) | 3 | sum 3 | s 3 || sr.agg(…) | | | |+-------------+-------------+-------------+---------------++-------------+-------------+-------------+---------------+| | 'rank' | ['rank'] | {'r': 'rank'} |+-------------+-------------+-------------+---------------+| sr.apply(…) | | rank | || sr.agg(…) | x 1 | x 1 | r x 1 || sr.trans(…) | y 2 | y 2 | y 2 |+-------------+-------------+-------------+---------------+- Last result has a hierarchical index. Use
'<Sr>[key_1, key_2]'to get its values.
Table with labeled rows and columns.
>>>DataFrame([[1,2], [3,4]],index=['a','b'],columns=['x','y'])xya12b34
<DF>=DataFrame(<list_of_rows>)# Rows can be either lists, dicts or series.<DF>=DataFrame(<dict_of_columns>)# Columns can be either lists, dicts or series.
<el>=<DF>.loc[row_key,column_key]# Or: <DF>.iloc[row_index, column_index]<Sr/DF>=<DF>.loc[row_key/s]# Or: <DF>.iloc[row_index/es]<Sr/DF>=<DF>.loc[:,column_key/s]# Or: <DF>.iloc[:, column_index/es]<DF>=<DF>.loc[row_bools,column_bools]# Or: <DF>.iloc[row_bools, column_bools]
<Sr/DF>=<DF>[column_key/s]# Or: <DF>.column_key<DF>=<DF>[row_bools]# Keeps rows as specified by bools.<DF>=<DF>[<DF_of_bools>]# Assigns NaN to False values.
<DF>=<DF>><==<el/Sr/DF># Returns DataFrame of bools.<DF>=<DF>+-*/<el/Sr/DF># Non-matching keys get value NaN.
<DF>=<DF>.set_index(column_key)# Replaces row keys with values from a column.<DF>=<DF>.reset_index()# Moves row keys to their own column.<DF>=<DF>.filter('<regex>',axis=1)# Only keeps columns whose key matches the regex.<DF>=<DF>.melt(id_vars=column_key/s)# Converts DF from wide to long format.
>>>l=DataFrame([[1,2], [3,4]],index=['a','b'],columns=['x','y'])xya12b34>>>r=DataFrame([[4,5], [6,7]],index=['b','c'],columns=['y','z'])yzb45c67
+------------------------+---------------+------------+------------+--------------------------+| | 'outer' | 'inner' | 'left' | Description |+------------------------+---------------+------------+------------+--------------------------+| l.merge(r, on='y', | x y z | x y z | x y z | Joins/merges on column. || how=…) | 0 1 2 . | 3 4 5 | 1 2 . | Also accepts left_on and || | 1 3 4 5 | | 3 4 5 | right_on parameters. || | 2 . 6 7 | | | Uses 'inner' by default. |+------------------------+---------------+------------+------------+--------------------------+| l.join(r, lsuffix='l', | x yl yr z | | x yl yr z | Joins/merges on row keys.|| rsuffix='r', | a 1 2 . . | x yl yr z | 1 2 . . | Uses 'left' by default. || how=…) | b 3 4 4 5 | 3 4 4 5 | 3 4 4 5 | || | c . . 6 7 | | | |+------------------------+---------------+------------+------------+--------------------------+| pd.concat([l, r], | x y z | y | | Adds rows at the bottom. || axis=0, | a 1 2 . | 2 | | Uses 'outer' by default. || join=…) | b 3 4 . | 4 | | By default works the || | b . 4 5 | 4 | | same as `l.append(r)`. || | c . 6 7 | 6 | | |+------------------------+---------------+------------+------------+--------------------------+| pd.concat([l, r], | x y y z | | | Adds columns at the || axis=1, | a 1 2 . . | x y y z | | right end. || join=…) | b 3 4 4 5 | 3 4 4 5 | | Uses 'outer' by default. || | c . . 6 7 | | | |+------------------------+---------------+------------+------------+--------------------------+| l.combine_first(r) | x y z | | | Adds missing rows and || | a 1 2 . | | | columns. || | b 3 4 5 | | | || | c . 6 7 | | | |+------------------------+---------------+------------+------------+--------------------------+<Sr>=<DF>.sum/max/mean/idxmax/all()# Or: <DF>.apply/agg/transform(<agg_func>)<DF>=<DF>.rank/diff/cumsum/ffill/interpl()# Or: <DF>.apply/agg/transform(<trans_func>)<DF>=<DF>.fillna(<el>)# Or: <DF>.applymap(<map_func>)
- All operations operate on columns by default. Use
'axis=1'parameter to process the rows instead.
>>>df=DataFrame([[1,2], [3,4]],index=['a','b'],columns=['x','y'])xya12b34
+-------------+-------------+-------------+---------------+| | 'sum' | ['sum'] | {'x': 'sum'} |+-------------+-------------+-------------+---------------+| df.apply(…) | | x y | || df.agg(…) | x 4 | sum 4 6 | x 4 || | y 6 | | |+-------------+-------------+-------------+---------------++-------------+-------------+-------------+---------------+| | 'rank' | ['rank'] | {'x': 'rank'} |+-------------+-------------+-------------+---------------+| df.apply(…) | x y | x y | x || df.agg(…) | a 1 1 | rank rank | a 1 || df.trans(…) | b 2 2 | a 1 1 | b 2 || | | b 2 2 | |+-------------+-------------+-------------+---------------+- Use
'<DF>[col_key_1, col_key_2][row_key]'to get the fifth result's values.
<DF>=pd.read_json/html('<str/path/url>')<DF>=pd.read_csv/pickle/excel('<path/url>')<DF>=pd.read_sql('<query>',<connection>)<DF>=pd.read_clipboard()
<dict>=<DF>.to_dict(['d/l/s/sp/r/i'])<str>=<DF>.to_json/html/csv/markdown/latex([<path>])<DF>.to_pickle/excel(<path>)<DF>.to_sql('<table_name>',<connection>)
Object that groups together rows of a dataframe based on the value of the passed column.
>>>df=DataFrame([[1,2,3], [4,5,6], [7,8,6]],index=list('abc'),columns=list('xyz'))>>>df.groupby('z').get_group(3)xya12>>>df.groupby('z').get_group(6)xyb45c78
<GB>=<DF>.groupby(column_key/s)# DF is split into groups based on passed column.<DF>=<GB>.get_group(group_key)# Selects a group by value of grouping column.
<DF>=<GB>.sum/max/mean/idxmax/all()# Or: <GB>.apply/agg(<agg_func>)<DF>=<GB>.rank/diff/cumsum/ffill()# Or: <GB>.aggregate(<trans_func>)<DF>=<GB>.fillna(<el>)# Or: <GB>.transform(<map_func>)
>>>gb=df.groupby('z')xyz3:a1236:b456c786
+-------------+-------------+-------------+-------------+---------------+| | 'sum' | 'rank' | ['rank'] | {'x': 'rank'} |+-------------+-------------+-------------+-------------+---------------+| gb.agg(…) | x y | x y | x y | x || | z | a 1 1 | rank rank | a 1 || | 3 1 2 | b 1 1 | a 1 1 | b 1 || | 6 11 13 | c 2 2 | b 1 1 | c 2 || | | | c 2 2 | |+-------------+-------------+-------------+-------------+---------------+| gb.trans(…) | x y | x y | | || | a 1 2 | a 1 1 | | || | b 11 13 | b 1 1 | | || | c 11 13 | c 1 1 | | |+-------------+-------------+-------------+-------------+---------------+Object for rolling window calculations.
<R_Sr/R_DF/R_GB>=<Sr/DF/GB>.rolling(window_size)# Also: `min_periods=None, center=False`.<R_Sr/R_DF>=<R_DF/R_GB>[column_key/s]# Or: <R>.column_key<Sr/DF/DF>=<R_Sr/R_DF/R_GB>.sum/max/mean()# Or: <R>.apply/agg(<agg_func/str>)
# $ pip3 install pandas plotlyimportpandasaspdimportplotly.expresscovid=pd.read_csv('https://covid.ourworldindata.org/data/owid-covid-data.csv',usecols=['iso_code','date','total_deaths','population'])continents=pd.read_csv('https://datahub.io/JohnSnowLabs/country-and-continent-codes-'+ \'list/r/country-and-continent-codes-list-csv.csv',usecols=['Three_Letter_Country_Code','Continent_Name'])df=pd.merge(covid,continents,left_on='iso_code',right_on='Three_Letter_Country_Code')df=df.groupby(['Continent_Name','date']).sum().reset_index()df['Total Deaths per Million']=df.total_deaths*1e6/df.populationdf=df[('2020-03-14'<df.date)& (df.date<'2020-06-25')]df=df.rename({'date':'Date','Continent_Name':'Continent'},axis='columns')plotly.express.line(df,x='Date',y='Total Deaths per Million',color='Continent').show()
# $ pip3 install pandas plotlyimportpandasaspdimportplotly.graph_objectsasgoimportdatetimedefmain():data=scrape_data()df=wrangle_data(*data)display_data(df)defscrape_data():defscrape_yahoo(id_):BASE_URL='https://query1.finance.yahoo.com/v7/finance/download/'now=int(datetime.datetime.now().timestamp())url=f'{BASE_URL}{id_}?period1=1579651200&period2={now}&interval=1d&events=history'returnpd.read_csv(url,usecols=['Date','Close']).set_index('Date').Closecovid=pd.read_csv('https://covid.ourworldindata.org/data/owid-covid-data.csv',usecols=['date','total_cases'])covid=covid.groupby('date').sum()dow,gold,bitcoin= [scrape_yahoo(id_)forid_in ('^DJI','GC=F','BTC-USD')]dow.name,gold.name,bitcoin.name='Dow Jones','Gold','Bitcoin'returncovid,dow,gold,bitcoindefwrangle_data(covid,dow,gold,bitcoin):df=pd.concat([dow,gold,bitcoin],axis=1)df=df.sort_index().interpolate()df=df.rolling(10,min_periods=1,center=True).mean()df=df.loc['2020-02-23':].iloc[:-2]df= (df/df.iloc[0])*100returnpd.concat([covid,df],axis=1,join='inner')defdisplay_data(df):defget_trace(col_name):returngo.Scatter(x=df.index,y=df[col_name],name=col_name,yaxis='y2')traces= [get_trace(col_name)forcol_nameindf.columns[1:]]traces.append(go.Scatter(x=df.index,y=df.total_cases,name='Total Cases',yaxis='y1'))figure=go.Figure()figure.add_traces(traces)figure.update_layout(yaxis1=dict(title='Total Cases',rangemode='tozero'),yaxis2=dict(title='%',rangemode='tozero',overlaying='y',side='right'),legend=dict(x=1.1) ).show()if__name__=='__main__':main()
Library that compiles Python code into C.
# $ pip3 install cythonimportpyximport;pyximport.install()import<cython_script><cython_script>.main()
- All
'cdef'definitions are optional, but they contribute to the speed-up. - Script needs to be saved with a
'pyx'extension.
cdef<type><var_name>=<el>cdef<type>[n_elements]<var_name>= [<el_1>,<el_2>, ...]cdef<type/void><func_name>(<type><arg_name_1>, ...):
cdefclass<class_name>:cdefpublic<type><attr_name>def__init__(self,<type><arg_name>):self.<attr_name>=<arg_name>
cdefenum<enum_name>:<member_name_1>,<member_name_2>, ...
$ pip3 install pyinstaller$ pyinstaller script.py# Compiles into './dist/script' directory.$ pyinstaller script.py --onefile# Compiles into './dist/script' console app.$ pyinstaller script.py --windowed# Compiles into './dist/script' windowed app.$ pyinstaller script.py --add-data'<path>:.'# Adds file to the root of the executable.
- File paths need to be updated to
'os.path.join(sys._MEIPASS, <path>)'.
#!/usr/bin/env python3## Usage: .py#fromcollectionsimportnamedtuplefromdataclassesimportmake_dataclassfromenumimportEnumfromsysimportargv,exitimportredefmain():pass##### UTIL#defread_file(filename):withopen(filename,encoding='utf-8')asfile:returnfile.readlines()if__name__=='__main__':main()
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