Parses a pattern and checks if the given string matches that pattern

pattern_parser.py

def is_matching(cand):
    """Parses a composite `cand` and check if the string matches
    the pattern. E.g.,
        cand = "++$*+*{2} xm4cccdvv" -> True.
    `cand` is a pattern and a string separated by a space. Each "+"
    in the pattern means an alphabetic character in the string; each
    "$" means a numeric character (1-9); each "*" means an alphabetic
    character repeated N times with N >= 1 if it is followed by "{N}"
    and otherwise an alphabetic character repeated 3 times.
    """
    pattern, s = cand.split()
    p_idx, s_idx = 0, 0
    while p_idx < len(pattern) and s_idx < len(s):
        if pattern[p_idx] == "+":
            if not s[s_idx].isalpha():
                return False
            p_idx += 1
            s_idx += 1
        elif pattern[p_idx] == "$":
            if not s[s_idx].isnumeric():
                return False
            p_idx += 1
            s_idx += 1
        elif pattern[p_idx] == "*":
            if pattern[p_idx + 1] == "{":
                closing_pos = p_idx + pattern[p_idx:].index("}")
                num = int(pattern[p_idx + 2 : closing_pos])
                p_idx = closing_pos + 1
            else:
                num = 3
                p_idx += 1
            repeating_part = s[s_idx: s_idx + num]
            if not repeating_part.isalpha() or repeating_part != repeating_part[0] * num:
                return False
            s_idx += num
    if p_idx != len(pattern) or s_idx != len(s):
        return False
    return True