All versions of a possibly replacements

Question

I have a small trouble with one problem:

For example, we have string 'YXY00' . Every 'X' of 'Y' may be replaced with 'Y' or 'X' respectively. In this example we have 2^3 = 8 options of replacement, like:

YXY00
YXX00
YYY00
YYX00
XXY00
XXX00
XYY00
XYX00

How can I get this replacements with Python 3.x?

Answer 1

You can use itertools.permutations() to get the permutations of a string. Then by applying some substitution logic, you can end up with the following:

import itertools

def permutate(source, changeset):
    count = sum(1 for char in source if char in changeset)
    holder = ''.join('{}' if char in changeset else char for char in source)
    for perm in set(itertools.permutations(changeset * count, count)):
        print(holder.format(*perm))

permutate('XY000Y00', 'XY')

Result:

XY000X00
XX000Y00
XY000Y00
XX000X00
YX000X00
YY000Y00
YX000Y00
YY000X00

Answer 2

I refactored some more, now it is more readable:

def replace_at_index(string, index, replacement):
    """
    Credit to: http://stackoverflow.com/users/95612/jochen-ritzel

    >>> replace_at_index("abc", 1, "z")
    'azc'
    """
    return string[:index] + replacement + string[index + 1:]

def possible_replaces(string):
    """
    >>> list(possible_replaces('YXY00'))
    ['XXY00', 'YXY00', 'YXY00', 'YYY00', 'YXX00', 'YXY00', 'YXY00', 'YXY00']
    >>> list(possible_replaces('XYY000000'))
    ['XYY000000', 'YYY000000', 'XXY000000', 'XYY000000', 'XYX000000', 'XYY000000', 'XYY000000', 'XYY000000', 'XYY000000', 'XYY000000', 'XYY000000', 'XYY000000']
    """
    for index, char in enumerate(string):
        if char in 'XY':
            yield replace_at_index(string, index, 'X')
            yield replace_at_index(string, index, 'Y')
        else:
            yield string

---

I also wrote a more general solution:

def possible_replaces(string, to_multipy_replace = 'XY'):
    """
    Returns a list of strings where each member of `to_multipy_replace` is replaced
    by each member of said set.

    >>> list(possible_replaces('YXY00'))
    ['XXY00', 'YXY00', 'YXY00', 'YYY00', 'YXX00', 'YXY00', 'YXY00', 'YXY00']
    >>> list(possible_replaces('XYY0'))
    ['XYY0', 'YYY0', 'XXY0', 'XYY0', 'XYX0', 'XYY0', 'XYY0']
    """
    for index, char in enumerate(string):
        if char in to_multipy_replace:
            for replacement in to_multipy_replace:
                yield replace_at_index(string, index, replacement)
        else:
            yield string

You are now not limited to 'XY' only but any charset that pleases you.