Functions

Syntax

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

Example

def printme( str ):
   "This prints a passed string into this function"
   print str
   return

All parameters in the Python language are passed by reference.
Maintain reference of the passed object and append values in the same object.

def changeme( mylist ):
   "This changes a passed list into this function"
   mylist.append([1,2,3,4]);
   print "Values inside the function: ", mylist
   return

Reference is being overwritten inside the called function.

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

Function Arguments

Required arguments
Required arguments are the arguments passed to a function in correct positional order, otherwise it gives a syntax error.
Keyword arguments
Keyword arguments are related to the function calls. When you use keyword arguments in a function call, the caller identifies the arguments by the parameter name.

# Function definition is here
def printinfo( name, age ):
   "This prints a passed info into this function"
   print "Name: ", name
   print "Age ", age
   return;
# Now you can call printinfo function
printinfo( age=50, name="miki" )

Default arguments
A default argument is an argument that assumes a default value if a value is not provided in the function call for that argument.

# Function definition is here
def printinfo( name, age = 35 ):
   "This prints a passed info into this function"
   print "Name: ", name
   print "Age ", age
   return;
# Now you can call printinfo function
printinfo( age=50, name="miki" )
printinfo( name="miki" )

Variable-length arguments
Syntax:

def functionname([formal_args,] *var_args_tuple ):
   "function_docstring"
   function_suite
   return [expression]

An asterisk * is placed before the variable name that holds the values of all nonkeyword variable arguments. This tuple remains empty if no additional arguments are specified during the function call.
Example:

# Function definition is here
def printinfo( arg1, *vartuple ):
   "This prints a variable passed arguments"
   print "Output is: "
   print arg1
   for var in vartuple:
      print var
   return;
# Now you can call printinfo function
printinfo( 10 )
printinfo( 70, 60, 50 )

Anonymous Functions

You can use the lambda keyword to create small anonymous functions.
Syntax:

lambda [arg1 [,arg2,.....argn]]:expression

Example:

# Function definition is here
sum = lambda arg1, arg2: arg1 + arg2;
# Now you can call sum as a function
print "Value of total : ", sum( 10, 20 )
print "Value of total : ", sum( 20, 20 )