Please show me a regex parser in 18 lines of code! Even 36! I did this exercise once and it took 100s of lines, I think using C++... but it's been a long time. Maybe it's significantly shorter in Python? But still 18 lines is impressive.
def matches(pattern, s):
if len(pattern) == 0:
return True
c = pattern[0]
assert c not in ("*", "?")
if len(pattern) > 1:
if pattern[1] == "?":
return (
len(s) > 0 and c in (".", s[0]) and matches(pattern[2:], s[1:])
) or matches(pattern[2:], s)
elif pattern[1] == "*":
for i, d in enumerate(s):
if c not in (".", d):
break
return any(matches(pattern[2:], s[j:]) for j in range(i, -1, -1))
return len(s) > 0 and c in (".", s[0])