Output

# Lines that begin with a '#' are called comments# They're ignored by Python and used for documentation# This line prints "hello"print("hello")print(1234)

Variables

foo=1234# Create a variable called foo whose value is 1234print(foo)name="hello"# Create a variable called nameprint(name)

Input

number=input("Please enter a number: ")print(number)name=input("What is your name? ")print("hello "+name)

Primitive Data Types

# Boolean (True/False) valuesprint(True)print(False)is_hungry=Trueprint(is_hungry)# Toggle between True/False using 'not'is_hungry=notis_hungryprint(is_hungry)# Integersprint(1+1)# Additionprint(999)# Other numbersprint(1e4)# Scientific notation 1e4 is 1000print(1_000_000)# Python ignores _ in numbersprint(-42)# Negative Numbersprint(12-2)# Subtractionprint(12*2)# Multiplicationprint(12//2)# Integer division, converts result to int# Floats aka Floating Point Numbersprint(3.14159)# Approximation of piprint(1/3)# Converts a rational number into imprecise "float" valueprint(12/2)# Regular division, converts to floatprint(13/2)# Regular divisionprint(round(2.3))# Round a number from float to intprint(round(2.7))# Round another number from float to int# Stringslanguage="python"print(language)letters="abcd1234"print(letters)number_string="1234"print(number_string)

Type Conversion

type(23)type(3.14)type(True)type(-12.4)type("hello")type("a")# Convert from float to intnumber=int(3.14)type(number)# Convert from int to floatnumber=float(3)type(number)# Convert from string to intnumber=int("1234")type(number)# Convert from string to floatnumber=float("12.345")type(number)# Convert from bool to stringvalue=str(True)type(value)# Convert from string to boolvalue=bool('False')# Convert from int to boolbool(0)bool(1)bool(5)bool(-2)# Convert from float to boolbool(0.0)bool(0.1)bool(-0.0)# Weird behaviour:1234+True# gives 1235 because "True" is 1 internally.1234+5*True# gives 12391234-True# gives 12331234/False# gives ZeroDivisionError

Collections 1 (tuple and list)

Tuples

# A tuple is a read-only data structure for storing collections that# don't need to be changed. You create one using ( and ) characters.# Create a tuple with ( and )my_tuple= (1,2,"hello",3.14,False,"hello")print(type(my_tuple))# Access an item by index using [ and ]. Indexes start at 0print(my_tuple[0])print(my_tuple[3])print(my_tuple[10])# IndexError.# Access a container from right-to-leftprint(my_tuple[-1])print(my_tuple[-3])# Count number of items in a tuplemy_tuple.count("hello")my_tuple.count(3.14)my_tuple.count("blahblah")# Search and get the index of an itemmy_tuple.index("hello")my_tuple.index(3.14)my_tuple.index(False)my_tuple.index("blah")# ValueError.# Trying to change the value of an item in a tuple causes an error.my_tuple[2]="newvalue"# TypeError.# Warning: If creating a tuple with only 1 item, you need to use this special syntax with a comma.my_tuple2= (42, )type(my_tuple2)# is a 'tuple' type# If you forget the comma, then Python doesn't create the tuple.fake_tuple= (42)type(fake_tuple)# is an 'int' type

Lists

# Unlike arrays in most other languages, Python lists can store data of any type.# Create a list with [ and ]my_list= [1,2,"this is a list",4.56,True]# Lists have the following methods:# append, clear, copy, count, extend, index, insert, pop, remove, reverse, sort# Accessing an item in a list using index, same as tuples.my_list[2]# displays "this is a list"# Appending an item (only 1 item can be appended at a time).my_list.append(123)# Appends 123 on to the end of the list.# Insert an item at a particular index.my_list.insert(0,'hello')# inserts 'hello' at the beginning (index 0) of list.my_list.insert(2,'blahblah')# inserts 'blahblah' at index 2.# "pop" an item from a list, which accesses an item and removes it.# defaults to end of list if no index is given as an argument.my_list.pop()# removes last item from the listmy_list.pop(2)# gets and removes item at index 2# "remove" differs from pop. pop uses an index. remove searches for the value and removes the first instance of it.my_list.remove("hello")# searches for "hello" and removes 1st instance if found.# Reverse the list (changes the actual list "in place").my_list.reverse()# Sort the list in ascending order. Advanced sorting can control how it'ssorted.my_list.sort()# Copy the list. Returns a "shallow copy". Read more about what this meanslater.my_list2=my_list.copy()# Count the number of occurrences of a value.my_list.count("hello")# Extend the list, aka add multiple items at a time.my_list.extend(["x",102,False])# Return the first index of a value. (without changing the list)my_list.index("hello")# You can also tell it where to start/stop searching.# Clear the list.my_list.clear()

Collections 2 (set and dictionary)

Sets

# A set is an unordered collection of things without duplicates.# Python will automatically remove duplicates from a set.# Important methods you can use on sets are: add, difference,# intersection, union. Run help(set) for others.# Create two setsset_a= {'Apple','Banana','Carrot','Banana'}# duplicate gets removedset_b= {'Carrot','Date','Elderberry'}# Add an itemset_b.add('Hamster')# Remove an itemset_b.remove('Date')# Perform a "union" operation on the sets, aka join them together and return a new set.set_a.union(set_b)# Perform an "intersection" operation, aka return the set of items in both sets.set_a.intersection(set_b)# Perform a "set difference" operation on the two sets. (objects in set A but not set B)set_a.difference(set_b)# Objects only in one or the other, but not both.set_a.symmetric_difference(set_b)# See help(set) for more methods. These are the most common ones though.# You can also perform these operations on multiple sets at a time using operators.set_c= {'Banana','Elderberry','Plum'}# & is intersection. Items only in all sets.set_a&set_b&set_c# | is union. Join all sets together.set_a|set_b|set_c# - is difference (not-symmetric). Items in A but not others.set_a-set_b-set_c# ^ is symmetric difference. Items unique to each set but not overlapping.set_a^set_b^set_c

Dictionaries

# Dictionaries are a key-value object in Python.# Like sets, you create them using { and }, but unlike sets, they must be# created as key-value pairs using the : symbol.# The values used can be any object.my_dictionary= {'banana':'$10.00','cheese':True}# Access items like with lists, except keys are usually strings.my_dictionary['banana']# returns the string '$10.00'my_dictionary['cheese']# returns True# If accessing a key that doesn't exist using [ ], Python raises a KeyError.# e.g. my_dictionary['optimus'] will raise a KeyError.# Adding new items.my_dictionary['optimus']='Truck'# Changing existing items.my_dictionary['cheese']=False# Get all the keys. (used for looping/iterating later on)my_dictionary.keys()# Get all the values.my_dictionary.values()# Get all the items (key-value pairs)my_dictionary.items()# See help(dict) for other methods.

Conditionals / Control Flow Basics

magic_word=input('Please enter the magic word: ')ifmagic_word=='Ni!':print('We are the knights who say Ni!')else:print('Bring me a shrubbery!')

Looping Basics

# The easiest possible loop is an "infinite loop".# Press Ctrl-C to stop it.whileTrue:print('looping')

number=1whilenumber<100:print(number)number=number+1

number=1whileTrue:print(number)number=number+1ifnumber>=20:break

# Skip printing all numbers between 10 and 40number=1whilenumber<=50:number=number+1if10<number<40:print('skipping')continue# continue from next iteration of the loopprint(number)

my_list= [1,2,'hello',4]# How does Python know what 'something' is?# Try a different name instead of 'something' here.# Any name will work. It gets reassigned on each iteration.forsomethinginmy_list:print(something)

foriinrange(1,10):print(i)

# Exercise: Create a program that runs forever until the user entersacorrectword.# Hint: use input(), a while loop, and an if statement.

TBD

whilefor/inrange()break/continuepassmatchenumerate()ListComprehensions