sys module provides a function
setrecursionlimit that lets you change Python’s maximum recursion limit. The docs say:
The highest possible limit is platform-dependent.
My question is: What is the highest possible limits for various platforms, under CPython? I would like to know the values for Linux, Mac and Windows.
UPDATE: Can we please avoid “You’re doing it wrong” answers? I know that trying to do very deep recursion is usually a bad idea. I’ve considered the pros and cons in my specific situation and decided that I want to do it.
On Windows (at least),
sys.setrecursionlimit isn’t the full story. The hard limit is on a per-thread basis and you need to call
threading.stack_size and create a new thread once you reach a certain limit. (I think 1MB, but not sure) I’ve used this approach to increase it to a 64MB stack.
import sys import threading threading.stack_size(67108864) # 64MB stack sys.setrecursionlimit(2 ** 20) # something real big # you actually hit the 64MB limit first # going by other answers, could just use 2**32-1 # only new threads get the redefined stack size thread = threading.Thread(target=main) thread.start()
I haven’t tried to see what limits there might be on
threading.stack_size, but feel free to try… that’s where you need to look.
sys.setrecursionlimit is just a limit enforced by the interpreter itself.
threading.stack_size lets you manipulate the actual limit imposed by the OS. If you hit the latter limit first, Python will just crash completely.
You shouldn’t overuse recursive calls in CPython. It has not tail optimization, the function calls use a lot of memory and processing time. Those limits might not apply to other implementations, it’s not in the blueprints.
In CPython, recursion is fine for traversing data structures (where a limit of 1000 should be enough for everybody) but not for algorithms. If I were to implement, say, graph related algorithms and hit the recursion limit, I would either implement my own stack and use iterations, or look for libraries implemented in C/C++/whatever before raising the limit by hand.