Recursion is a process where a function calls itself directly or indirectly. It is implemented in Python through recursive functions, where a function calls itself. As an example, a recursive function is provided to calculate the factorial of a number by recursively calling itself and multiplying the number by the factorial of the number below it until reaching the base case of 1. For recursion to terminate, there must be a base case condition specified. The Python interpreter limits recursion depth to 1000 by default to avoid stack overflows from infinite recursion.

1. GVK CHINMAYA VIDYALAYA
SENIOR SECONDARY SCHOOL
Kothuru, Indukurupet, SPS Nellore
Recursion
Class: 12 Subject: Python Teacher: C Vijaya
B.Tech, MBA

2. What is recursion?
Recursion is the process of defining something in terms of itself.
A physical world example would be to place two parallel mirrors facing each other. Any object in
between them would be reflected recursively.

3. Python Recursive Function
In Python, we know that a function can call other functions. It is even possible for the function to call
itself. These types of construct are termed as recursive functions.
The following image shows the working of a recursive function called recurse.

4. Following is an example of a recursive function to find the factorial of an integer.
Factorial of a number is the product of all the integers from 1 to that number. For example, the
factorial of 6 (denoted as 6!) is 1*2*3*4*5*6 = 720.

6. When we call this function with a positive integer, it will recursively call itself by decreasing the number.
Each function multiplies the number with the factorial of the number below it until it is equal to one. This
recursive call can be explained in the following steps.

8. Our recursion ends when the number reduces to 1. This is called the base condition.
Every recursive function must have a base condition that stops the recursion or else the function calls itself
infinitely.
The Python interpreter limits the depths of recursion to help avoid infinite recursions, resulting in stack
overflows.
By default, the maximum depth of recursion is 1000. If the limit is crossed, it results in RecursionError. Let's
look at one such condition.

10. Example of Recursion
# This is python program to print
a pattern

11. Example of Recursion Def steps(1):
if(true):
x=1
while(true):
print(1)
x=2
a=2
steps(2)
Def steps(2):
if(true):
x=1
while(true):
print(1)
x=2
while(true)
print(2)
x=3
a=3
steps(3)
Def steps(3):
if(true)
x=1
while(true):
print(1)
x=2
While (true)
print(2)
Python Program to
print pattern

12. Recursion refers to a programming technique in which a function calls itself either
directly or indirectly

18. ● 1st Fibonacci number = 0 (by assumption)
● 2nd Fibonacci number = 1 (by assumption)
● 3rd Fibonacci number = 1st + 2nd
= 0 + 1
= 1
● 4th Fibonacci number = 2nd + 3rd
= 1 + 1
= 2
● 5th Fibonacci number = 3rd + 4th
= 1 + 2
= 3
● 6th Fibonacci number = 4th + 5th
= 2 + 3
= 5

19. Iterative binary
search

20. Recursive
binary search