Python: Recursion depth exceeded error

Question

I reworked the program to get large prime numbers. Now it works fine, except I get a large number of red phrases at the end, after all the output is printed. Could someone please tell me why?

The end is of the output is:

(100000939.0, 'is prime')
(100000963.0, 'is prime')
(100000969.0, 'is prime')

The error is

Traceback (most recent call last):
  File "C:/Users/Marcela/Documents/Prime numbers to 100", line 48, in <module>
    loopfunction()
  File "C:/Users/Marcela/Documents/Prime numbers to 100", line 35, in loopfunction
    loopfunction()
  File "C:/Users/Marcela/Documents/Prime numbers to 100", line 35, in loopfunction
    loopfunction()
  File "C:/Users/Marcela/Documents/Prime numbers to 100", line 35, in loopfunction
    loopfunction()
...(many lines of it, the int ends with:) 
File "C:/Users/Marcela/Documents/Prime numbers to 100", line 13, in loopfunction
    while index <= 200000000.0:
RuntimeError: maximum recursion depth exceeded in cmp

Here is the script:

from __future__ import division
import sys
index=100000000.0
checker=2.0



def loopfunction():
    global index
    global checker
    checker=2

    while index <= 200000000.0:

        if index>=200000001:
            sys.exit(1)
        while checker<=14473.0:

            div = index/checker
            roundiv=round(index/checker, 0)
            if index == 1:
                print (index, "is prime")
                checker=2
                index=index+1
                loopfunction()   
            if checker == index:
                print (index, "is prime")
                checker=2
                index=index+1
                loopfunction()
            if roundiv==div:

                checker=2
                index=index+1
                loopfunction()    

            if checker==14473.0:

                print (index, "is prime")
                checker=2
                index=index+1
                loopfunction()

            checker = checker +1



loopfunction()

RuntimeError: maximum recursion depth exceeded while calling a Python object, that's your error really, the other lines are due to that — theBigChalk
– theBigChalk, Commented Jun 16, 2012 at 23:46
Thanks -- is there is way to avoid exceeding the maximum recursion depth? To me it seems like the script is logical. — user1460981
– user1460981, Commented Jun 16, 2012 at 23:51
The "red stuff" is: (100000937.0, 'is prime') (100000939.0, 'is prime') (100000963.0, 'is prime') (100000969.0, 'is prime') Traceback (most recent call last): File "C:/Users/Marcela/Documents/Prime numbers to 100", line 48, in <module> loopfunction() File "C:/Users/Marcela/Documents/Prime numbers to 100", line 35, in loopfunction loopfunction() ......(lots more the same!)... File "C:/Users/Marcela/Documents/Prime numbers to 100", line 13, in loopfunction while index <= 200000000.0: RuntimeError: maximum recursion depth exceeded in cmp — user1460981
– user1460981, Commented Jun 16, 2012 at 23:52
A better suggestion would be to convert recursion to iteration. — UltraInstinct
– UltraInstinct, Commented Jun 17, 2012 at 0:05

Blckknght · Accepted Answer · 2012-06-17 01:39:48Z

2

You can fix your recursion limit issue by simply not recursing. Your code already has the loops you need.

Just change the calls to loopfunction() in the various if statements to break.

While that is all that is needed to make the code function, I've noticed though that some of number of your if statements are unnecessary (either redundant with the loop conditions, or simply impossible to ever hit). You're also using while loops where for _ in range() loops would make more sense. Here's a greatly simplified version of your code, with some things renamed to clarify their purposes:

from math import sqrt

def primeFinder(start, end):
    prime = True

    for index in range(start, end):
        for checker in range(2, int(sqrt(index))+1):
            if index % checker == 0:
                prime = False
                break

        if prime:
            print("%d is prime" % index)

        prime = True

primetest(100000000, 200000001)

This version will still take a very long time (probably hours). If you really want to test a hundred million values for primeness, you should probably investigate a better algorithm, such as the Sieve of Eratosthenes.

edited Jun 17, 2012 at 1:39

answered Jun 17, 2012 at 0:54

Blckknght

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1 Comment

user1460981 Over a year ago

EXCELLENT!! I changed those three instances to "break" and it works like a charm, with numbers of ANY size. No more red phrases. You are a lifesaver, and great kudos to you my friend! Your own ode is more streamlined and better, but to get a grip on this I still wanted to know why my own wasn't working -- just change the function calls to break and presto.

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