Find all list permutations of splitting a string in Python

Question

I have a string of letters that I\'d like to split into all possible combinations (the order of letters must be remain fixed), so that:

s = \'monkey\'
         


        

Answer 1

The idea is to realize that the permutation of a string s is equal to a set containing s itself, and a set union of each substring X of s with the permutation of s\X. For example, permute('key'):

1. {'key'} # 'key' itself
2. {'k', 'ey'} # substring 'k' union 1st permutation of 'ey' = {'e, 'y'}
3. {'k', 'e', 'y'} # substring 'k' union 2nd permutation of 'ey' = {'ey'}
4. {'ke', 'y'} # substring 'ke' union 1st and only permutation of 'y' = {'y'}
5. Union of 1, 2, 3, and 4, yield all permutations of the string key.

With this in mind, a simple algorithm can be implemented:

>>> def permute(s):
    result = [[s]]
    for i in range(1, len(s)):
        first = [s[:i]]
        rest = s[i:]
        for p in permute(rest):
            result.append(first + p)
    return result

>>> for p in permute('monkey'):
        print(p)    

['monkey']
['m', 'onkey']
['m', 'o', 'nkey']
['m', 'o', 'n', 'key']
['m', 'o', 'n', 'k', 'ey']
['m', 'o', 'n', 'k', 'e', 'y']
['m', 'o', 'n', 'ke', 'y']
['m', 'o', 'nk', 'ey']
['m', 'o', 'nk', 'e', 'y']
['m', 'o', 'nke', 'y']
['m', 'on', 'key']
['m', 'on', 'k', 'ey']
['m', 'on', 'k', 'e', 'y']
['m', 'on', 'ke', 'y']
['m', 'onk', 'ey']
['m', 'onk', 'e', 'y']
['m', 'onke', 'y']
['mo', 'nkey']
['mo', 'n', 'key']
['mo', 'n', 'k', 'ey']
['mo', 'n', 'k', 'e', 'y']
['mo', 'n', 'ke', 'y']
['mo', 'nk', 'ey']
['mo', 'nk', 'e', 'y']
['mo', 'nke', 'y']
['mon', 'key']
['mon', 'k', 'ey']
['mon', 'k', 'e', 'y']
['mon', 'ke', 'y']
['monk', 'ey']
['monk', 'e', 'y']
['monke', 'y']