Recursionerror That Happens Only Without A Debugger

I am working on something that needs a recursive calling. The bigger app crashed. While minimizing a problem, I am experiencing a rather strange phenomena. consider the following c

Solution 1:

When a debugger proper is not usable for any reason, you have the oldest, most venerable, reliable and time-proven debugging technique: debug printing.

E.g. make the functions report the recursion depth:

def merge(A, s, m, e, r):
    print("merge: %d"%r)
    <...>

def mergesort(A, s, e, r=0):
    print("mergesort: %d"%r)
    <...>
        mergesort(A, s, m, r+1)
        mergesort(A, m+1, e, r+1)
        merge(A, s, m, e, r+1)
    <...>

And compare the outputs with and without the debugger if you're wondering what changes. Or just the faulty output to diagnose the problem -- whichever you think is a better investment of your time.