decompression.py

#  https://techdevguide.withgoogle.com/resources/compress-decompression/#!
def decomp(s,i = None):
    i = [0] if i is None else i
        number = 0
    out = []
    while i[0] < len(s):
        c = s[i[0]]
        i[0] += 1
        if c == ']':
            return out
        elif c == '[':
            out += decomp(s,i) * number
            number = 0
        elif c.isdigit():
            number *= 10
            number += int(c)
        else:
            out.append(c)
    return ''.join(out)
  
  
decomp("3[abc]4[ab]c")
decomp('2[3[a]b]x')
decomp('2[0[abcd]]') # inner bracket 0 times, thus '', outer bracket empty