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

A string (as opposed to list) oriented approach is to think of the each adjacent pair of characters being separated by either a space or empty string. That can be mapped to 1 and 0, and the number of possible splits are a power of 2:

2 ^ (len(s)-1)

for example, "key" can have '' or ' ' separating 'ke' and a '' or ' ' separating 'ey' which leads to 4 possibilities:

• key ('' between 'k' and 'e', '' between 'e' and 'y')
• k ey (' ' between 'k' and 'e', '' between 'e' and 'y')
• k e y (' ' between 'k' and 'e', ' ' between 'e' and 'y')
• ke y ('' between 'k' and 'e', ' ' between 'e' and 'y')

An unreadable python one liner that gives you a generator in string form:

operator_positions = (''.join([str(a >> i & 1).replace('0', '').replace('1', ' ') + s[len(s)-1-i] for i in range(len(s)-1, -1, -1)]) for a in range(pow(2, len(s)-1)))

A readable version of this generator with comments and sample:

s = 'monkey'
s_length = len(s)-1  # represents the number of ' ' or '' that can split digits

operator_positions = (
    ''.join(
        [str(a >> i & 1).replace('0', '').replace('1', ' ') + s[s_length-i]
         for i in range(s_length, -1, -1)])   # extra digit is for blank string to always precede first digit
    for a in range(pow(2, s_length))   # binary number loop
)
for i in operator_positions:
    print i

str(a >> i & 1) converts a into a binary string, which then has it's 0's and 1's replaced by '' and ' ', respectively. The binary string is an extra digit long so that the first digit is always ''. That way, as the digit splitter is combined with the first character, it always results in just the first character.