Python, IDLE: Too many recursive errors

Question

This is supposedly a problem with the IDLE editor for Python. (I'm running Python 3.3.0 on OSX, but the same problem occurs with 2.7.3)

I'm using IDLE to write Python programs. My problem is: Calling a recursive function, which calls itself too many times (1000 times), doesn't give me a single runtime error, but rather, it keeps sending me error messages until I close the program.

The error which it should be sending is: "RuntimeError: maximum recursion depth exceeded." The error which it sends a thousand times isntead is simply a point out to where in the script the problem is:

Traceback (most recent call last):
  File "<pyshell#112>", line 1, in <module>
    factorial(1.5)
  File "/Users/User/Documents/Python/Scripts/program1.py", line 187, in factorial
    recurse = factorial(n-1)
  File "/Users/User/Documents/Python/Scripts/program1.py", line 187, in factorial
    recurse = factorial(n-1)

etc.

This goes with all recursive functions calling itself too many times, but the specific function used here is:

def factorial(n):
    if n == 0:
        return 1
    else:
        recurse = factorial(n-1)
        result = n * recurse
        return result

related : http://stackoverflow.com/questions/2401447/python-recursive-function-error-maximum-recursion-depth-exceeded — Ashwini Chaudhary, Mar 15 '13 at 18:08
related: http://stackoverflow.com/questions/8177073/python-maximum-recursion-depth-exceeded — Ashwini Chaudhary, Mar 15 '13 at 18:08
It looks like IDLE is printing out every single stack frame (of which there are many). I don't know if there's a way to limit how many frames it prints. — NPE, Mar 15 '13 at 18:09

Ashwini Chaudhary · Accepted Answer · 2013-03-15T18:29:55.120

1

To stop python from showing those hundreds of errors, you can use a try-except block:

def factorial(n):
    if n == 0:
        return 1
    else:
        recurse = factorial(n-1)
        result = n * recurse
        return result
try:
    print (factorial(6000))
except RuntimeError as e:
    print (e)

output:

#print factorial(1000)
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000

#print factorial(6000)
maximum recursion depth exceeded in comparison

In your case this error occurs because python has a limit on the maximum recursion depth,it is there to stop the C stack from overflow. But you can change it using sys.setrecursionlimit:

In [4]: import sys

In [5]: sys.getrecursionlimit()
Out[5]: 1000

edited Mar 15 '13 at 18:29

answered Mar 15 '13 at 18:16

Ashwini Chaudhary

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Thanks, but this gives me a syntax error for an unknown reason. – kongehund Mar 15 '13 at 18:25
@user2175018 python version? in py3.x use `print()` as a function. – Ashwini Chaudhary Mar 15 '13 at 18:26
Thanks, oversaw a missing (). Python 3.3.0 – kongehund Mar 15 '13 at 18:31
@kongehund what output do you expect here? – Ashwini Chaudhary Mar 15 '13 at 18:33
The error, which it gives me is: AttributeError: 'RuntimeError' object has no attribute 'message' – kongehund Mar 15 '13 at 18:39
I'm not sure how it's supposed to work, but it currently simply outputs the message "maximum recursion depth exceeded in comparison" when I launch the program. If I call factorial(6000), it still outputs tons of errors. – kongehund Mar 15 '13 at 18:48
@kongehund I think you're not doing it properly, it works fine on my system and on ideone too. http://ideone.com/B611ng – Ashwini Chaudhary Mar 15 '13 at 18:51
That's odd, though. I copied the code on ideone, put it into a new script, yet when I do >>>factorial(6000), it still spams me with error messages. Thanks anyway – kongehund Mar 15 '13 at 18:56
You've to put the call to `factorial` function inside the try-except, just calling `factorial(6000)` is always going to throw those errors. – Ashwini Chaudhary Mar 15 '13 at 19:03
Thank you, it works now. I don't quite understand how, though. Final script: http://ideone.com/Ovysgi – kongehund Mar 15 '13 at 19:15
Sure thing, it worked, but it fixed the function, rather than IDLE. Guess I'll have to use this every time I make a recursive function, then. – kongehund Mar 15 '13 at 19:23

score 0 · Answer 2 · answered Mar 15 '13 at 18:13

0

Problem is that you are trying to use a float and the code does not handle that. So, 1.5 -1 becomes 0.5, which causes the first recursive call. Then, 0.5 -1 becomes -0.5, which causes the further recursive calls.

Just in order to handle that, use:-

if n<=0: return 1

answered Mar 15 '13 at 18:13

GodMan

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Thanks for your answer, but I'm hoping to fix it, rather than avoid it. – kongehund Mar 15 '13 at 18:52
Oh, well my problem isn't that I don't know what causes the errors, but rather, the fact that the program sends me 1000 error messages instead of 1. Adding your code to the function fixes the function, but I'm trying to make IDLE send me 1 error message instead of 1000, when it goes beyond the maximum amount of recursive calls. – kongehund Mar 15 '13 at 19:03
In that case, please edit your question clearly explaining this – GodMan Mar 15 '13 at 19:16
Oh, I thought my question was understandable. It should be clearer now, though. – kongehund Mar 15 '13 at 19:34

Python, IDLE: Too many recursive errors

2 Answers2