Why Does My Recursive Python Function Return `None` Sometimes?

Understanding Recursion and Why It Returns None

When a function calls itself, it is known as recursion. This can be a powerful technique, but it's crucial to understand the concept of return values to prevent encountering unexpected results.

In the given Python code:

def get_input():
    my_var = input('Enter "a" or "b": ')

    if my_var != "a" and my_var != "b":
        print('You didn\'t type "a" or "b". Try again.')
        get_input()
    else:
        return my_var

print('got input:', get_input())

If the user inputs "a" or "b", the function works as intended and returns the input. However, an issue arises when the user inputs an invalid character and then a valid input. The problem stems from the recursive call in the if condition.

When my_var is not "a" or "b", the function correctly prompts the user to try again. However, the recursive call to get_input() lacks a return statement for the recursive function's return value. Without a proper return, Python implicitly returns None when the function falls off the end.

To fix this, the recursive call should be modified to return the result of the recursive function:

if my_var != "a" and my_var != "b":
    print('You didn\'t type "a" or "b". Try again.')
    return get_input()

With this change, the function will correctly return my_var after the user provides a valid input, preventing the return of None.

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