Python Recursion Function

Recursion is a powerful technique in programming where a function calls itself during its execution. A recursive function allows you to break down a complex problem into simpler sub-problems by calling itself repeatedly.

Basic syntax of a recursive function

1def recursive_function(parameters):
2    if base_case_condition(parameters):
3        return base_case_value
4    recursive_function(modified_parameters)

The recursive function should have two cases, a base case where it returns a value without calling itself, and a recursive case where it calls itself with modified parameters until it reaches the base case.

Example: Factorial of a number using recursion

1def factorial(n):
2    if n == 1:
3        return 1
4    else:
5        return n * factorial(n-1)
6
7print(factorial(5))

Output:

1120

In the above example, we have a function factorial that calculates the factorial of a given number n recursively. If n is equal to 1, it returns 1, otherwise it calls itself with the modified parameter n-1 until it reaches the base case where n is equal to 1.

Example: Fibonacci sequence using recursion

1def fibonacci(n):
2    if n == 1 or n == 2:
3        return 1
4    else:
5        return fibonacci(n-1) + fibonacci(n-2)
6
7for i in range(1, 11):
8    print(fibonacci(i), end=" ")

Output:

11 1 2 3 5 8 13 21 34 55

In the above example, we have a function fibonacci that calculates the nth number in the Fibonacci sequence recursively. If n is equal to 1 or 2, it returns 1, otherwise it calls itself with the modified parameters n-1 and n-2 until it reaches the base case where n is equal to 1 or 2.

Recursion is a very powerful technique, but it should be used with caution as it can easily lead to infinite loops if not implemented properly.