Python Functions

• def functionname( parameters ):
    "function_docstring"
    function_suite
    return [expression]

  Example

  def printme( str ):
    "This prints a passed string into this function"
    print str
    return
  
  #!/usr/bin/python
  
  # Function definition is here
  def printme( str ):
    "This prints a passed string into this function"
    print str;
    return;
  
  # Now you can call printme function
  printme("I'm first call to user defined function!");
  printme("Again second call to the same function");

• Output

  I'm first call to user defined function!
  Again second call to the same function

• Pass by reference vs value:

  #!/usr/bin/python
  
  # Function definition is here
  def changeme( mylist ):
     "This changes a passed list into this function"
     mylist.append([1,2,3,4]);
     print "Values inside the function: ", mylist
     return
  
  # Now you can call changeme function
  mylist = [10,20,30];
  changeme( mylist );
  print "Values outside the function: ", mylist

• Output

  Values inside the function: [10, 20, 30, [1, 2, 3, 4]]
  Values outside the function: [10, 20, 30, [1, 2, 3, 4]]


• There is one more example where argument is being passed by reference but inside the function, but the reference is being over-written.
  #!/usr/bin/python
  # Function definition is here
  def changeme( mylist ):
     "This changes a passed list into this function"
     mylist = [1,2,3,4]; # This would assig new reference in mylist
     print "Values inside the function: ", mylist
     return
  # Now you can call changeme function
  mylist = [10,20,30];
  changeme( mylist );
  print "Values outside the function: ", mylist

• Output

  Values inside the function: [1, 2, 3, 4]
  Values outside the function: [10, 20, 30]