Inner Functions

Introduction:

  • In Python, you can define functions inside other functions. These are called inner functions.
  • Inner functions can be useful for keeping code modular and organized.

Example:

  • Let's define a function with two inner functions.

Python Program:

python
def function():
    print('Inside function.')

    def innerFunction1():
        print('Inner function 1.')

    def innerFunction2():
        print('Inner function 2.')

    innerFunction1()
    innerFunction2()

function()

Output:

 
Inside function.
Inner function 1.
Inner function 2.

Explanation:

  1. We define a function named function().
  2. Inside function(), we define two inner functions: innerFunction1() and innerFunction2().
  3. We call these inner functions within function().
  4. Finally, we call function().

Working of Inner Functions:

  • Let's understand how the inner functions work using the above example:
    1. Define function().
    2. Call function().
    3. Execute print('Inside function.').
    4. Define innerFunction1().
    5. Define innerFunction2().
    6. Call innerFunction1() and execute print('Inner function 1.').
    7. Call innerFunction2() and execute print('Inner function 2.').

Scope of Inner Functions:

  • Inner functions are only visible inside the outer function in which they are defined. You cannot call them outside the outer function.

Example: Calling Inner Function from Outside:

  • If you try to call an inner function from outside its scope, a NameError will be raised.

Python Program:

python
def function():
    print('Inside function.')

    def innerFunction1():
        print('Inner function 1.')

    def innerFunction2():
        print('Inner function 2.')

    innerFunction1()
    innerFunction2()

innerFunction1()  # This will raise an error

Output:

 
Traceback (most recent call last):
  File "example.py", line 13, in <module>
    innerFunction1()
NameError: name 'innerFunction1' is not defined

Exercises:

  1. Create a Function with Inner Function:

    • Write a function outer() with two inner functions inner1() and inner2(). Call both inner functions inside outer().

      python
      def outer():
    def inner1():
        print('This is inner function 1.')

    def inner2():
        print('This is inner function 2.')

    inner1()
    inner2()

outer()
  2. Return Inner Function:

    • Write a function outer() that returns one of its inner functions based on an argument.

      python
      def outer(choice):
    def inner1():
        return 'This is inner function 1.'

    def inner2():
        return 'This is inner function 2.'

    if choice == 1:
        return inner1
    else:
        return inner2

func = outer(1)
print(func())

Summary:

  • In this tutorial, we learned how to define inner functions and their scope in a Python program. Practice writing inner functions to understand how they can help keep your code organized and modular!