The document discusses the basics of functions in Python, including what a function is, the advantages of using functions, how to define and call functions, and how to use parameters, return values, global variables, default arguments, keyword arguments, and docstrings when working with functions. Key points covered include how functions allow code reuse and decomposition of complex problems, how to define a function using the def keyword, how to call a defined function by name, and how docstrings provide documentation for functions and other objects.

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Python Programming Essentials - M17 - Functions

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  http://www.skillbrew.com/SkillbrewTalent brewed bytheindustry itselfFunctions in PythonPavan Verma@YinYangPavan1Founder, P3 InfoTech Solutions Pvt. Ltd.Python Programming Essentials
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  © SkillBrew http://skillbrew.comWhatis a functionA function is a block of organized, reusable codethat is used to perform a single, related action2
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  © SkillBrew http://skillbrew.comAdvantagesof using functions3Reusability. Reducingduplication of codeDecomposingcomplex problemsinto simpler piecesAbstraction Cleaner code
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  © SkillBrew http://skillbrew.comTypesof functionsTypes ofFunctionsBuilt-inFunctionsUser DefinedFunctions4
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  © SkillBrew http://skillbrew.comDefininga function5def functionName():# do somethingdef printList():num_list = range(3)print num_list1. def keyword is used to define a function2. def keyword is followed by a function name3. Function name is followed by parenthesis ()4. After this a block of python statements
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  © SkillBrew http://skillbrew.comCallinga Function6def printList():num_list = range(3)print num_listprintList()Output:[0, 1, 2]To call a function, we specify the function namewith the round bracketsCall to function
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  © SkillBrew http://skillbrew.comreturnkeyword7def printList():num_list = range(3)return num_listmy_list = printList()print my_listOutput:[0, 1, 2]1. The return keyword isused to return valuesfrom a function2. A function implicitlyreturns None by defaulteven if you don’t usereturn keyword
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  © SkillBrew http://skillbrew.comParameterizedfunctions8def printList(upper_limit):num_list = range(upper_limit)print "list: %s" % num_listprintList(5)printList(2)Output:list: [0, 1, 2, 3, 4]list: [0, 1]1. Names given in thefunction definitionare calledparameters2. The values yousupply in thefunction call arecalledarguments
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  © SkillBrew http://skillbrew.comDefaultarguments9def printList(upper_limit=4):print "upper limit: %d" % upper_limitnum_list = range(upper_limit)print "list: %s" % num_listprintList(5)printList()Output:upper limit: 5list: [0, 1, 2, 3, 4]upper limit: 4list: [0, 1, 2, 3]value 41. When function is calledwithout any arguments defaultvalue is used2. During a function call ifargument is passed then thepassed value is used
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  © SkillBrew http://skillbrew.comDefaultarguments (2)10A non-default argument may not follow defaultarguments while defining a functiondef printList(upper_limit=4, step):
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  © SkillBrew http://skillbrew.comKeywordarguments11def printList(upper_limit, step=1):print "upper limit: %d" % upper_limitnum_list = range(0, upper_limit, step)print "list: %s" % num_listprintList(upper_limit=5, step=2)Output:upper limit: 5list: [0, 2, 4]range() function has two variations:1.range(stop)2.range(start, stop[, step])
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  © SkillBrew http://skillbrew.comKeywordarguments (2)12printList(step=2, upper_limit=5)printList(upper_limit=5, step=2)Advantages of using keyword argumentsUsing the function is easier since you don’t have to worryabout or remember the order of the arguments
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  © SkillBrew http://skillbrew.comKeywordarguments (3)13You can give values to only those parameters which youwant, provided that the other parameters have defaultargument valueprintList(upper_limit=5)
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  © SkillBrew http://skillbrew.comKeywordarguments (4)14A non-keyword argument cannot follow keywordarguments while calling a functionprintList(upper_limit=4, 10)
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  © SkillBrew http://skillbrew.comglobalvariables15counter = 10def printVar():print counterprintVar()print "counter: %d" % counterOutput:10counter: 10Variable defined outside a function or class is aglobal variablecounter is aglobal variable
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  © SkillBrew http://skillbrew.comglobalvariables (2)16counter = 10def printVar():counter = 20print "Counter in: %d" % counterprintVar()print "Counter out: %d" % counterOutput:Counter in: 20Counter out: 10counter in function definition islocal variable tied to function’snamespaceHence the value of globalcounter does not gets modified
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  © SkillBrew http://skillbrew.comglobalvariables (3)17counter = 10def printVar():global countercounter = 20print "Counter in: %d" % counterprintVar()print "Counter out: %d" % counterOutput:Counter in: 20Counter out: 20In order to use the globalcounter variable inside the functionyou have to explicitly tell python to useglobal variable using global keyword
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  © SkillBrew http://skillbrew.comdocstrings18defadd(x, y):""" Return the sum of inputs x, y"""return x + yprint add.__doc__Python documentation strings (or docstrings) provide aconvenient way of associating documentation with Pythonmodules, functions, classes, and methodsdocstringAccess a docstring usingobject.__doc__
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  © SkillBrew http://skillbrew.comSummaryWhat is a function Advantages of usingfunctions Defining a function Calling a function return keyword19 Parameterized functions Default arguments Keyword arguments global variables docstrings
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  © SkillBrew http://skillbrew.comResourcesDefault argumentshttp://www.ibiblio.org/g2swap/byteofpython/read/default-argument-values.html Keyword argumentshttp://www.ibiblio.org/g2swap/byteofpython/read/keyword-arguments.html return keywordhttp://www.ibiblio.org/g2swap/byteofpython/read/return.html local variables http://www.ibiblio.org/g2swap/byteofpython/read/local-variables.html Docstringshttp://www.ibiblio.org/g2swap/byteofpython/read/docstrings.html20
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