Runtimeerror: Maximum Recursion Limit Reached in Python

In this article, we will elucidate the Runtimeerror: Maximum Recursion Limit Reached In Python through examples, and we will also explore potential approaches to resolve this issue.

What is Runtimeerror: Maximum Recursion Limit Reached?

When you run a Python program you may see Runtimeerror: Maximum Recursion Limit Reached. It indicates that the execution of your program has surpassed 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).

Syntax :

RecursionError: maximum recursion depth exceeded

Why does Runtimeerror: Maximum Recursion Limit Reached occur?

There are various reasons for Runtimeerror: Maximum Recursion Limit Reached in Python. Here we are explaining some common reasons for the occurrence of Runtimeerror: Maximum Recursion Limit Reached:

• 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 Runtimeerror: Maximum Recursion Limit Reached

Python3

def endless_recursion(n):
    """A recursive function without a proper base case"""
    return n * endless_recursion(n-1)

print(endless_recursion(5))

Output

 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 ‘RuntimeError: Maximum Recursion Limit Reached’

Python3

def countdown(n):
    if n > 0:
# Here we dont reduce n so it leads to infinite loop
        print(n)
        countdown(n)
# Example usage with n=5
n=5
countdown(n)

Output

 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 ‘RuntimeError: Maximum Recursion Limit Reached’.

Python3

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)

# Testing the factorial function
result = factorial(1001)
print(result)

Output

Here we are calling factorial with a large value of n, that why we encounter a RecursionError.

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 RuntimeError: Maximum Recursion Limit Reached

Below are some of the ways by which we can fix RuntimeError: Maximum Recursion Limit Reached in Python:

• Adding a base case
• Increasing the recursion limit
• Using an iterative approach

Adding a Base Case

One effective way to prevent RuntimeError: Maximum Recursion Limit Reached 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):
    # Base case: when n is 0, return 1
    if n == 0:
        return 1

    # Recursive call
    return n * factorial_recursive_with_base_case(n - 1)

if __name__ == '__main__':
    # Example: calculating the factorial of 100
    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

# importing the sys module
import sys

sys.setrecursionlimit(10**6)

def fact(n):

    if(n == 0):
        return 1

    return n * fact(n - 1)

if __name__ == '__main__':

    # taking input
    f = 1001

    print(fact(f))

Output

40278964733717086731724613635692698970509423907492534717634371034036845091102764961263625269545637420528046859880739325469029853986780336746022515349961453558842192859116083367874245135491592125229928...

Using Iteration Instead of Recursion

Another effective way to address RuntimeError: Maximum Recursion Limit Reached is to convert the recursive solution into an iterative one, using loops instead of recursive calls.

Python3

# Function to calculate the factorial of a number using an iterative approach
def factorial_iterative(n):
    # Initialize the result to 1
    result = 1

    # Iterate from 1 to n (inclusive)
    for i in range(1, n + 1):
        # Multiply the current result by the current value of i
        result *= i

    # Return the final result after the loop
    return result

#Examples

result = factorial_iterative(1001)

print(result)

Output

40278964733717086731724613635692698970509423907492534717634371034036845091102764961263625269545637420528046859880739325469029853986780336746022515349961453558842192859116083367874245135491592125229928...

Conclusion

In this article we discussed about ways How To Fix Obscure Runtimeerror: Maximum Recursion Limit Reached in Python. It involves understanding its root causes, such as missing base cases or improper recursive logic. By incorporating base cases, adjusting recursive logic, or switching to iterative approaches, developers can effectively resolve the error and ensure that recursive functions terminate appropriately, preventing infinite loops and stack overflow.