Question

I have a string (of undertermined length) that I want to copy a lot of times replacing one character at a time from an array (of undertermined length) of characters.

So say I have this string: ‘aa’
And this array: [‘a’, ‘b’, ‘c’, ‘d’]

after some magic for-looping stuff there would be an array like: [‘aa’, ‘ab’, ‘ac’, ‘ad’, ‘ba’, ‘bb’ … ‘dc’, ‘dd’]

How would you do this? I tried something using three for loops but I just can’t seem to get it.

Edit
The dependency on the string is the following:

Say the string is: ‘ba’
then the output should be: [‘ba’, ‘bb’, ‘bc’, ‘bd’, ‘ca’ … ‘dd’]

Answer 1

If an order of strings in the result array doesn’t matter and all chars from the initial string are in the substitution array then:

#!/usr/bin/env python from itertools import product  def allreplacements(seed, replacement_chars):     assert all(c in replacement_chars for c in seed)     for aset in product(replacement_chars, repeat=len(seed)):         yield ''.join(aset)  print(list(allreplacements('ba', 'a b c d'.split()))) # ['aa', 'ab', 'ac', 'ad', 'ba', 'bb', 'bc', 'bd', 'ca', 'cb', 'cc', #  'cd', 'da', 'db', 'dc', 'dd'] 

---

Here’s a solution for a general case. Replacements are performed in a lexicographic order:

#!/usr/bin/env python from itertools import product  def allreplacements(seed, replacement_chars):     '''Generate all possible replacements (with duplicates).'''     masks = list(product(range(2), repeat=len(seed))) # e.g., 00 01 10 11     for subs in product(replacement_chars, repeat=len(seed)):         for mask in masks:             # if mask[i] == 1 then replace seed[i] by subs[i]             yield ''.join(s if m else c for s, m, c in zip(subs, mask, seed))  def del_dups(iterable):     '''Remove duplicates while preserving order.      http://stackoverflow.com/questions/89178/in-python-what-is-the-fastest-algorithm-for-removing-duplicates-from-a-list-so#282589     '''     seen = {}     for item in iterable:         if item not in seen:            seen[item] = True            yield item  print(list(del_dups(allreplacements('ba', 'abcd')))) print(list(del_dups(allreplacements('ef', 'abcd')))) # ['ba', 'aa', 'bb', 'ab', 'bc', 'ac', 'bd', 'ad', 'ca', 'cb', 'cc', #  'cd', 'da', 'db', 'dc', 'dd']  # ['ef', 'ea', 'af', 'aa', 'eb', 'ab', 'ec', 'ac', 'ed', 'ad', 'bf', #  'ba', 'bb', 'bc', 'bd', 'cf', 'ca', 'cb', 'cc', 'cd', 'df', 'da', #  'db', 'dc', 'dd']