简单功能的正则表达式引擎实现

import sys

def match_star(c, reg_exp, text):

while True:
if match_here(reg_exp, text):
return True

if len(text) > 0 and (c == text[0] or c == '.'):
text = text[1:]
else:
break

return False

def match_here(reg_exp, text):

if len(reg_exp) == 0:
return True

if len(reg_exp) > 1 and reg_exp[1] == '*':
return match_star(reg_exp[0], reg_exp[2:], text)

if reg_exp[0] == '$':
return len(text) == 0

if reg_exp[0] == '.' and len(text) > 0:
return match_here(reg_exp[1:], text[1:])

if reg_exp[0] == text[0] and len(text) > 0:
return match_here(reg_exp[1:], text[1:])

return False

if __name__ == '__main__':
reg_exp = sys.argv[1]
text = sys.argv[2]

print(match_here(reg_exp, text))