Python Programming Essentials - M17 - Functions

Python Programming Essentials - M17 - Functions

• 1.
  http://www.skillbrew.com /SkillbrewTalent brewed bythe industry itself Functions in Python Pavan Verma @YinYangPavan 1 Founder, P3 InfoTech Solutions Pvt. Ltd. Python Programming Essentials
• 2.
  © SkillBrew http://skillbrew.com Whatis a function A function is a block of organized, reusable code that is used to perform a single, related action 2
• 3.
  © SkillBrew http://skillbrew.com Advantagesof using functions 3 Reusability. Reducing duplication of code Decomposing complex problems into simpler pieces Abstraction Cleaner code
• 4.
  © SkillBrew http://skillbrew.com Typesof functions Types of Functions Built-in Functions User Defined Functions 4
• 5.
  © SkillBrew http://skillbrew.com Defininga function 5 def functionName(): # do something def printList(): num_list = range(3) print num_list 1. def keyword is used to define a function 2. def keyword is followed by a function name 3. Function name is followed by parenthesis () 4. After this a block of python statements
• 6.
  © SkillBrew http://skillbrew.com Callinga Function 6 def printList(): num_list = range(3) print num_list printList() Output: [0, 1, 2] To call a function, we specify the function name with the round brackets Call to function
• 7.
  © SkillBrew http://skillbrew.com returnkeyword 7 def printList(): num_list = range(3) return num_list my_list = printList() print my_list Output: [0, 1, 2] 1. The return keyword is used to return values from a function 2. A function implicitly returns None by default even if you don’t use return keyword
• 8.
  © SkillBrew http://skillbrew.com Parameterizedfunctions 8 def printList(upper_limit): num_list = range(upper_limit) print "list: %s" % num_list printList(5) printList(2) Output: list: [0, 1, 2, 3, 4] list: [0, 1] 1. Names given in the function definition are called parameters 2. The values you supply in the function call are called arguments
• 9.
  © SkillBrew http://skillbrew.com Defaultarguments 9 def printList(upper_limit=4): print "upper limit: %d" % upper_limit num_list = range(upper_limit) print "list: %s" % num_list printList(5) printList() Output: upper limit: 5 list: [0, 1, 2, 3, 4] upper limit: 4 list: [0, 1, 2, 3] value 4 1. When function is called without any arguments default value is used 2. During a function call if argument is passed then the passed value is used
• 10.
  © SkillBrew http://skillbrew.com Defaultarguments (2) 10 A non-default argument may not follow default arguments while defining a function def printList(upper_limit=4, step):
• 11.
  © SkillBrew http://skillbrew.com Keywordarguments 11 def printList(upper_limit, step=1): print "upper limit: %d" % upper_limit num_list = range(0, upper_limit, step) print "list: %s" % num_list printList(upper_limit=5, step=2) Output: upper limit: 5 list: [0, 2, 4] range() function has two variations: 1.range(stop) 2.range(start, stop[, step])
• 12.
  © SkillBrew http://skillbrew.com Keywordarguments (2) 12 printList(step=2, upper_limit=5) printList(upper_limit=5, step=2) Advantages of using keyword arguments Using the function is easier since you don’t have to worry about or remember the order of the arguments
• 13.
  © SkillBrew http://skillbrew.com Keywordarguments (3) 13 You can give values to only those parameters which you want, provided that the other parameters have default argument value printList(upper_limit=5)
• 14.
  © SkillBrew http://skillbrew.com Keywordarguments (4) 14 A non-keyword argument cannot follow keyword arguments while calling a function printList(upper_limit=4, 10)
• 15.
  © SkillBrew http://skillbrew.com globalvariables 15 counter = 10 def printVar(): print counter printVar() print "counter: %d" % counter Output: 10 counter: 10 Variable defined outside a function or class is a global variable counter is a global variable
• 16.
  © SkillBrew http://skillbrew.com globalvariables (2) 16 counter = 10 def printVar(): counter = 20 print "Counter in: %d" % counter printVar() print "Counter out: %d" % counter Output: Counter in: 20 Counter out: 10 counter in function definition is local variable tied to function’s namespace Hence the value of global counter does not gets modified
• 17.
  © SkillBrew http://skillbrew.com globalvariables (3) 17 counter = 10 def printVar(): global counter counter = 20 print "Counter in: %d" % counter printVar() print "Counter out: %d" % counter Output: Counter in: 20 Counter out: 20 In order to use the global counter variable inside the function you have to explicitly tell python to use global variable using global keyword
• 18.
  © SkillBrew http://skillbrew.com docstrings 18 defadd(x, y): """ Return the sum of inputs x, y """ return x + y print add.__doc__ Python documentation strings (or docstrings) provide a convenient way of associating documentation with Python modules, functions, classes, and methods docstring Access a docstring using object.__doc__
• 19.
  © SkillBrew http://skillbrew.com Summary What is a function  Advantages of using functions  Defining a function  Calling a function  return keyword 19  Parameterized functions  Default arguments  Keyword arguments  global variables  docstrings
• 20.
  © SkillBrew http://skillbrew.com Resources Default arguments http://www.ibiblio.org/g2swap/byteofpython/read/default-argument- values.html  Keyword arguments http://www.ibiblio.org/g2swap/byteofpython/read/keyword- arguments.html  return keyword http://www.ibiblio.org/g2swap/byteofpython/read/return.html  local variables http://www.ibiblio.org/g2swap/byteofpython/read/local- variables.html  Docstrings http://www.ibiblio.org/g2swap/byteofpython/read/docstrings.html 20
• 21.
  21