Python 'RecursionError: maximum recursion depth exceeded' (or 'while calling a Python object'): how do I fix it without just raising sys.setrecursionlimit?

Cause: CPython counts nested Python calls and raises RecursionError (a subclass of RuntimeError) once the depth passes the interpreter's limit, which sys.getrecursionlimit() reports. The limit exists to stop runaway recursion from overflowing the C stack and crashing the process. Most real cases are a missing or wrong base case, a function that calls itself with the same argument, mutually recursive functions, or a property/__getattr__/__repr__ that accidentally calls itself. Genuinely deep but finite data (long linked lists, deep trees, nested JSON) can also hit it. Fix (best first): 1. Read the traceback: a repeating block of the same few lines means the recursion never reaches its base case. Print or log the argument at each call and confirm it shrinks toward the base case. In classes, check that __getattr__, __setattr__, __repr__ and property getters do not touch the attribute they define (use self.__dict__ or object.__getattribute__ instead). 2. If the data is legitimately deep, rewrite the algorithm as a loop with an explicit stack (a list or collections.deque) or use iteration for tail-style recursion. This has no depth limit besides memory. 3. For repeated sub-problems, add functools.lru_cache or a dict memo so the same calls are not expanded again (this reduces calls, but depth is unchanged). 4. Only as a last resort, raise the limit for a known bounded depth: import sys; sys.setrecursionlimit(5000). Python's docs warn that a limit set too high can crash the interpreter, that the highest usable value depends on the platform, and that this should be done with care. Do not set it to huge values to hide an infinite recursion. Verify: the function returns on your largest realistic input, and a test with an input twice as deep also passes without raising RecursionError or killing the process. Sources: https://docs.python.org/3/library/exceptions.html#RecursionError https://docs.python.org/3/library/sys.html#sys.setrecursionlimit