RecursionError: maximum recursion depth exceeded in comparison Python

Question

I'm trying to write a recursive function to print some sort of permutations in python. However I get maximum depth error for some reason.

def perm(chars, k, word):
   if k == 0:
      print(word)
   for char in chars:
      perm(chars, k - 1, char + word)


perm(['1','2'], 2, '')

Anyone has any idea what the error is?

ggorlen · Accepted Answer · 2018-11-15 22:18:01Z

6

You're missing a base case, causing your call stack to overflow. Add a base case by making the for loop (the recursive case) conditional:

def perm(chars, k, word):
   if k == 0:
       print(word)
   else:
       for char in chars:
           perm(chars, k - 1, char + word)


perm(['1','2'], 2, '')

Output:

Try it!

edited Nov 15, 2018 at 22:18

answered Nov 15, 2018 at 18:25

ggorlen

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2 Comments

user4464936 Over a year ago

yeah apparently i was just missing that else :)

Hollywood Over a year ago

Just to piggyback- OP, maximum recursion depth is almost always a telltale sign of an infinite loop. A common error that leads to infinite loops is incorrect base cases, as we have seen here

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