Python，IDLE：太多的递归错误

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

Answer 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

Answer 2

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