Why recursive lambda fails at an large number

Question

I want to caculate an church number by python below,but it prompt the errors when I use the input greater than 993,anyone whom had the experience told me what happend?

NUM0=lambda f: lambda x:x
SUCC=lambda n: lambda f: lambda x: f(n(f)(x))

def decoding(n):
    num=NUM0
    for i in xrange(n):
        num = SUCC(num)
    return num

def encoding(num):
    f=lambda x:x+1
    return str(num(f)(0))

print encoding(decoding(994)) # Why fails once greater than 993

The error traceback tells you exactly *"what happened"*: `maximum recursion depth exceeded`. What don't you understand? Have you read e.g. [this](http://stackoverflow.com/q/3323001/3001761)? — jonrsharpe, Sep 11 '14 at 15:09
[`sys.getrecursionlimit`](https://docs.python.org/2/library/sys.html#sys.getrecursionlimit), [`sys.setrecursionlimit`](https://docs.python.org/2/library/sys.html#sys.setrecursionlimit) — falsetru, Sep 11 '14 at 15:10
Python crashes intentionally when the call stack contains one thousand functions. This is so potentially infinite recursive calls don't gobble up all your available memory, or cause a far nastier crash on the C implementation level. — Kevin, Sep 11 '14 at 15:11
Fair,so an maximum recursion depth exist in python and can not be configured? — Mr.ke, Sep 11 '14 at 15:12
It can't be removed, but it can be raised. See falsetru's comment. — Kevin, Sep 11 '14 at 15:12

score 1 · Accepted Answer · edited May 23 '17 at 12:05

You get a maximum recursion depth exceeded because python tries to protect itself against possible infinite recursive calls. Basically it stops itself in order not to cause a crash that could be a lot worse.

You can change the recursion limit with sys.setrecursionlimit (as said by @falsetru).

But as @ThomasWouters said in this answer:

Doing so is dangerous -- the standard limit is a little conservative, but Python stackframes can be quite big."

Why recursive lambda fails at an large number

1 Answers1