How to generate all combinations of lower and upper characters in a word?

Question

How do you generate all combinations of lower and upper characters in a word? e.g:

'abc' → ['abc', 'ABC', 'Abc', 'ABc', 'aBC', 'aBc', 'abC', 'Abc']

'ab' → ['ab', 'AB', 'Ab', 'aB']

Answer 1

You can achieve this by zipping the upper and lower case letters and taking their cartesian product:

import itertools

chars = "abc"
results = list(map(''.join, itertools.product(*zip(chars.upper(), chars.lower()))))

print(results)
>>>['ABC', 'ABc', 'AbC', 'Abc', 'aBC', 'aBc', 'abC', 'abc']

---

To visualise how this works:

1. zip is creating our 3 'axes' for us, each with 2 points (the upper / lower cases)
   [('A', 'a'), ('B', 'b'), ('C', 'c')].
2. product takes the cartesian product of these axes, i.e. the 8 possible coordinates corresponding to the corners of the unit cube it creates:

1. Create axes	2. Take Cartesian product

Answer 2

Using recursion:

def foo(word):
    if len(word) == 1:
        return [word.lower(), word.upper()]
    else:
        return [f"{j}{i}" for j in foo(word[0]) for i in foo(word[1:])]

s = "abc"
print(foo(s))

>>> ['abc', 'abC', 'aBc', 'aBC', 'Abc', 'AbC', 'ABc', 'ABC']