Python port of regexp matcher from 'The Practice of Programming'

regexp_matcher.py

# Python port of Rob Pike's regexp matcher from 'The Practice of Programming'
# Idea for match() stolen from https://github.com/darius/sketchbook/blob/master/misc/pike.py

def match(re, text):
    """
    Search for regexp anywhere in text
    c - any literal character
    . - any single character
    ^ - the beginning of the input string
    $ - the end of the input string
    * - zero or more occurrences of the previous character
    """
    return (matchhere(re[1:], text) if re[0] == '^' else
            matchstar('.', re, text))

def matchhere(re, text):
    """Search for regexp at beginning of text"""
    if re == '':
        return True
    if re == '$':
        return text == ''
    if len(re) > 1 and re[1] == '*':
        return matchstar(re[0], re[2:], text)
    if text and (re[0] == '.' or re[0] == text[0]):
        return matchhere(re[1:], text[1:])
    return False

def matchstar(c, re, text):
    """Search for c*regexp at beginning of text"""
    for i in range(len(text)) or [0]:
        if matchhere(re, text[i:]):
            return True
        if text[i] != c and c != '.':
            return False
    return False

Empty text, damn. Thanks for pointing this out. If you don't mind I'll steal your idea to fix match().

This is only very slightly related, but would you like to review https://github.com/darius/peglet ? I'm trying to improve on the grammar parser from cs212 -- to make something more useful without making it less accessible.