The Python RecursionError is an exception that occurs when the maximum recursion depth is exceeded. This typically occurs when a function calls itself recursively, and the recursion doesn't have a proper stopping condition (base case).

What Causes RecursionError

A RecursionError in Python is caused by a function calling itself recursively without a proper base case. Python has a limit on the number of times a function can call itself recursively. This is to ensure that the function does not execute indefinitely. If this limit is exceeded by a recursive function, a RecursionError is raised.

Python RecursionError Example

Here’s an example of a Python RecursionError thrown when calling a recursive function that does not have a base case:

def func():
    func()

func()

Since the recursive function func() does not have a terminating condition, calling it creates an infinite loop as the function keeps calling itself over and over again until the RecursionError: maximum recursion depth exceeded error occurs:

Traceback (most recent call last):
  File "test.py", line 4, in <module>
    func()
  File "test.py", line 2, in func
    func()
  File "test.py", line 2, in func
    func()
  File "test.py", line 2, in func
    func()
  [Previous line repeated 996 more times]
RecursionError: maximum recursion depth exceeded

How to Fix RecursionError in Python

Here are some approaches to fix a recursion error in Python:

Adding a base case: The most common cause of a recursion error is that the function does not have a base case to stop the recursion. In such cases, a base case can be added to the function that stops recursion when a condition is met.
Increasing the recursion limit: Python has a default maximum recursion depth of 1000. If a function exceeds this limit, it can be increased using the sys.setrecursionlimit(n) function. Developers should be careful when increasing the limit as this can cause a crash if the recursion is not properly controlled.
Using an iterative approach: If a recursive approach is causing a recursion error, it may be possible to use an iterative approach instead e.g. a for or while loop. This can reduce the risk of hitting the maximum recursion depth, and in some cases can also lead to more efficient and easier to understand code.

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