How To Fix Recursionerror In Python
Last Updated :
02 Feb, 2024
In this article, we will elucidate the Recursionerror In Python through examples, and we will also explore potential approaches to resolve this issue.
What is Recursionerror In Python?
When you run a Python program you may see Recursionerror. So what is Recursionerror In Python? Python RecursionError exception is raised when the execution of your program exceeds the recursion limit of the Python interpreter. This typically occurs when a function calls itself recursively, and the recursion doesn’t have a proper stopping condition (base case).
Why does Recursionerror occur?
There are various reasons for Recursionerror in Python. Here we are explaining some common reasons for occurring Recursionerror:
- Missing Base Case
- Infinite Recursion:
- Exceeding Maximum Recursion Depth
Missing Base Case
As we all know the recursive function should include a base case that defines when the recursion should stop. However when we do not specify a base case, the function may keep calling itself indefinitely, leading to a ‘RecursionError.’
Python3
def endless_recursion(n):
return n * endless_recursion(n - 1 )
print (endless_recursion( 5 ))
|
Hangup (SIGHUP)
Traceback (most recent call last):
File "Solution.py", line 5, in <module>
print(endless_recursion(5))
File "Solution.py", line 3, in endless_recursion
return n * endless_recursion(n-1)
File "Solution.py", line 3, in endless_recursion
return n * endless_recursion(n-1)
File "Solution.py", line 3, in endless_recursion
return n * endless_recursion(n-1)
[Previous line repeated 996 more times]
RecursionError: maximum recursion depth exceeded
Infinite Recursion
This occurs when we incorrectly define recursive logic and it fails to make progress towards the base case can result in infinite recursion.This exhausts the call stack and results into ‘RecursionError.’
Python3
def countdown(n):
if n > 0 :
print (n)
countdown(n)
n = 5
countdown(n)
|
Hangup (SIGHUP)
Traceback (most recent call last):
File "Solution.py", line 8, in <module>
countdown(n)
File "Solution.py", line 5, in countdown
countdown(n)
File "Solution.py", line 5, in countdown
countdown(n)
File "Solution.py", line 5, in countdown
countdown(n)
[Previous line repeated 994 more times]
File "Solution.py", line 4, in countdown
print(n)
RecursionError: maximum recursion depth exceeded while getting the str of an object
Exceeding Maximum Recursion Depth
In Python, there is a limit on the maximum recursion depth to prevent stack overflow.If a recursive function exceeds this limit, Python raises a ‘RecursionError.’
Python3
def factorial(n):
if n = = 0 :
return 1
else :
return n * factorial(n - 1 )
result = factorial( 1001 )
print (result)
|
Here we are calling factorial with a large value of n, that why we encounter a RecursionError.
Hangup (SIGHUP)
Traceback (most recent call last):
File "Solution.py", line 8, in <module>
result = factorial(500000)
File "Solution.py", line 5, in factorial
return n * factorial(n-1)
File "Solution.py", line 5, in factorial
return n * factorial(n-1)
File "Solution.py", line 5, in factorial
return n * factorial(n-1)
[Previous line repeated 995 more times]
File "Solution.py", line 2, in factorial
if n == 0:
RecursionError: maximum recursion depth exceeded
Fix “RecursionError: Maximum Recursion Depth Exceeded” Error In Python
Below are some of the ways by which we can fix RecursionError in Python:
- Adding a base case
- Increasing the recursion limit
- Using an iterative approach
Adding a Base Case
One effective way to prevent RecursionError is to ensure that the recursive function has a proper stopping condition, commonly referred to as a base case. This ensures that the recursion stops when a certain condition is met.
Python3
def factorial_recursive_with_base_case(n):
if n = = 0 :
return 1
return n * factorial_recursive_with_base_case(n - 1 )
if __name__ = = '__main__' :
result = factorial_recursive_with_base_case( 100 )
print (result)
|
Output:
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
Increase Recursion Limit
The “sys” module in Python provides a function called setrecursionlimit() to modify the recursion limit in Python. It takes one parameter, the value of the new recursion limit. By default, this value is usually 10^3. If you are dealing with large inputs, you can set it to, 10^6 so that large inputs can be handled without any errors.
Python3
import sys
sys.setrecursionlimit( 10 * * 6 )
def fact(n):
if (n = = 0 ):
return 1
return n * fact(n - 1 )
if __name__ = = '__main__' :
f = 1001
print (fact(f))
|
Output:
4027896473371708673172461363569269897050942390749253471763437103403684509110276496126362526954563742052804685988073932546902985398678033674602251534996145355884219285911608336787424513549159212522992854569462713969958504379595406450196963727411427873474502813253243738244563002268716094314978269894891095227257916911679456985092824215386329665233766798918236969009820752……………………………………………
Using Iteration Instead of Recursion
Another effective way to address RecursionError is to convert the recursive solution into an iterative one, using loops instead of recursive calls.
Python3
def factorial_iterative(n):
result = 1
for i in range ( 1 , n + 1 ):
result * = i
return result
result = factorial_iterative( 1001 )
print (result)
|
Output:
4027896473371708673172461363569269897050942390749253471763437103403684509110276496126362526954563742052804685988073932546902985398678033674602251534996145355884219285911608336787424513549159212522992854569462713969958504379595406450196963727411427873474502813253243738244563002268716094314978269894891095227257916911679456985092824215386329665233766798918236969009820752……………………………………………
Conclusion
In this article we discussed about ‘RecursionError’ in Python involves understanding the root cause, which may include missing base cases or improper recursive logic. By incorporating base cases and adjusting recursive logic, developers can effectively fix ‘RecursionError’ and ensure that recursive functions terminate appropriately, preventing infinite loops and stack overflow.
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