Python sys.setrecursionlimit() method

The Python sys.setrecursionlimit() method is used to set the maximum depth of the Python interpreter stack to a specified limit. This is useful when dealing with recursive functions as Python's default recursion limit is relatively low i.e. usually 1000 which can cause a RecursionError for deep recursions.

By increasing the recursion limit using sys.setrecursionlimit(limit) we allow deeper recursions to occur without hitting the limit though it should be used with caution since excessively deep recursion can lead to a stack overflow and crash the program. Properly managing recursion depth is crucial to avoid infinite recursion and system instability.

Syntax

Following is the syntax and parameters of Python sys.setrecursionlimit() method −

sys.setrecursionlimit(limit)

Parameter

This method accepts an integer value that representing the new recursion limit.

Return value

This method does not return any value.

Example 1

Following is the example showing that the recursion limit is increased from the default 1000 to 2000 by allowing the recursive function to handle deeper recursions without triggering a RecursionError −

import sys

# Default recursion limit
print(sys.getrecursionlimit())  

# Set a new recursion limit
sys.setrecursionlimit(2000)
print(sys.getrecursionlimit())  

# Example of a recursive function
def recursive_function(n):
    if n == 0:
        return 0
    else:
        return 1 + recursive_function(n - 1)

try:
    print(recursive_function(1500))  
except RecursionError:
    print("Recursion limit exceeded")

Output

1000
2000
1500

Example 2

This example shows how to handle functions that require deeper recursion with the help of sys.setrecursionlimit() method −

import sys

# Function with deep recursion
def deep_recursion(n):
    if n == 0:
        return "Reached the end"
    else:
        return deep_recursion(n - 1)

# Try with default recursion limit
try:
    print(deep_recursion(1500))  # Likely to raise RecursionError
except RecursionError:
    print("RecursionError with default limit")

# Set a higher recursion limit
sys.setrecursionlimit(2000)

# Try again with higher limit
try:
    print(deep_recursion(1500))  # Should work without error
except RecursionError:
    print("RecursionError even with higher limit")

Output

RecursionError with default limit
Reached the end

Example 3

This example calculates the factorial of a large number showing the need to increase the recursion limit to handle large recursive computations −

import sys

# Factorial function with recursion
def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n - 1)

# Default recursion limit is usually sufficient
try:
    print(factorial(995))  # Should work fine
except RecursionError:
    print("Recursion limit exceeded")

# Increase recursion limit to handle larger inputs
sys.setrecursionlimit(1500)

try:
    print(factorial(1200))  # Should work now with increased limit
except RecursionError:
    print("Recursion limit exceeded even with higher limit")

Output

4064374293729118100717076205049963163696947795811066648039580324660695257469883785154417906181986826077637
-----------------
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0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000