String to regex converter

converter.py

import re


def _sub_special_chars_any(in_string: str):
    return re.sub("[^a-z\d\s]", ".?", in_string)
    

def _mark_substrings_optional(in_string: str, n=3):
    parts = in_string.split()
    if len(parts) == 1:
        return "\\b" + in_string + "\\b"
    mod = []
    for i, part in enumerate(parts):
        # see how many alphanumerics are in the part
        tmp = re.sub("[^a-z\d]", "", part)
        if len(tmp) <= n and i > 0:  # don't consider the first part of the string i.e ("AB Corporation")
            parts[i] = f"\s?({part})?\s?"
            mod.append(i)
    out = parts[0]
    # not using " ".join(parts) so we can detect
    # when not to inject a whitespace
    for i, part in enumerate(parts[1:]):
        if i+1 in mod:
            out = out + part
        else:
            out = out + " " + part
    out = re.sub(" ", "\\\s", out)
    return out


def convert(in_string: str):
    print(_mark_substrings_optional(_sub_special_chars_any(in_string.lower())))