Functions¶

Categories of Functions¶

Takes Something Returns Something.
Takes Something Returns Nothing
Takes Nothing Returns Nothing
Takes Nothing Returns Nothing

Syntax:

def func_name(arg):
   "function docstring"
    function_suite
    return [expression]

Example:

def myfunc(arg):
   "this function prints Hello Python"
    print(arg)
    return

Call a function
# Now you can call printme function
myfunc("This is ")

Pass by Reference vs Pass by Value¶

Example 1:

#!/usr/bin/python3

# Function definition is here
def mychange( mylist ):
   "This changes a passed list into this function"
   print ("Values inside the function before change: ", mylist)

   mylist[2]=5
   print ("Values inside the function after change: ", mylist)
   return

# Now you can call mychange function
mylist = [1,2,3]
mychange( mylist )
print ("Values outside the function: ", mylist)

Output:
Values inside the function before change:  [1, 2, 3]
Values inside the function after change:  [1, 2, 5]
Values outside the function:  [1, 2, 5]

Example 2:

#!/usr/bin/python3

# Function definition is here
def mychange( mylist ):
   "This changes a passed list into this function"
   mylist = [1,2,3,4] # This would assi new reference in mylist
   print ("Values inside the function: ", mylist)
   return

# Now you can call mychange function
mylist = [10,20,30]
mychange( mylist )
print ("Values outside the function: ", mylist)

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

Function Arguments¶

Required arguments
Keyword arguments
Default arguments
Variable-length arguments

1. Required arguments¶

#!/usr/bin/python3

    # 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()

Output:
Traceback (most recent call last):
   File "test.py", line 11, in <module>
      printme();
TypeError: printme() takes exactly 1 argument (0 given)

2. Keyword arguments¶

Example 1:

#!/usr/bin/python3

# 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( str = "Hello Python")

Output:
Hello Python

Example 2:

#!/usr/bin/python3

 # Function definition is here
 def printinfo( name, marks ):
    "This prints a passed info into this function"
    print ("Name: ", name)
    print ("Marks ", marks)
    return

 # Now you can call printinfo function
 printinfo( marks = 90, name = "Saurabh" )

 Output:
 Name:  Saurabh
 Age  90

3. Default arguments¶

#!/usr/bin/python3

# Function definition is here
def printinfo( name, marks = 35 ):
   "This prints a passed info into this function"
   print ("Name: ", name)
   print ("Marks ", marks)
   return

# Now you can call printinfo function
printinfo( marks = 90, name = "saurabh" )
printinfo( name = "James" )

Output:
Name:  Saurabh
Marks  50
Name:  James
Marks  35

4. Variable-length arguments¶

Syntax:

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

Example:

#!/usr/bin/python3

# 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( 90, 80, 70 )

Output is:
10
Output is:
90
80
70