Skip to content

Instantly share code, notes, and snippets.

@juanplopes

juanplopes/rex.py

Created May 9, 2020
Embed
What would you like to do?
# -*- coding: utf-8 -*-
from collections import deque
from functools import reduce
def rex(pattern):
tokens = deque(pattern)
def walk(chars):
while tokens and tokens[0] in chars:
yield tokens.popleft()
def option():
e = sequence()
for token in walk('|'):
e2 = sequence()
e = [(1, len(e)+2)] + e + [(len(e2)+1,)] + e2
return e
def sequence():
e = []
while tokens and tokens[0] not in '|)':
e += repetition()
return e
def repetition():
e = primary()
for token in walk('?*+'):
if token in '+*': e = e + [(1, -len(e))]
if token in '?*': e = [(1, len(e)+1)] + e
return e
def primary():
token = tokens.popleft()
if token == '.': return [None]
if token == '(': return [option(), tokens.popleft()][0]
if token not in '?*+)|': return [token]
raise Exception('Not expected: "{}"'.format(token))
e = option()
if tokens:
raise Exception('Not expected: "{}"'.format(''.join(tokens)))
return Machine(e)
class Machine(object):
def __init__(self, states):
self.states = states
self.n = len(states)
def matcher(self, string):
A, B, V = list(), list(), [-1]*len(self.states)
def addnext(start, i, j):
if j==self.n: return 1
if V[j] == i: return 0
V[j] = i
if isinstance(self.states[j], tuple):
return sum(addnext(start, i, j+k) for k in self.states[j])
B.append((start, j))
return 0
def key(a): return (a[1]-a[0], -a[0]) if a else (0, 0)
answer = None
for i, c in enumerate(string):
addnext(i, i, 0)
yield i, answer, B
A, B = B, A
del B[:]
for start, j in A:
if self.states[j] in (None, c) and addnext(start, i+1, j+1):
answer = max(answer, (start, i+1), key=key)
yield len(string), answer, B
def match(self, string):
return reduce(lambda _, s: s[1], self.matcher(string), None)
def source(self):
for s in self.states:
yield ('JUMP ' if isinstance(s, tuple) else 'CONSUME ') + str(s)
yield 'MATCH!'
def __repr__(self):
return '\n'.join('{:04d}: {}'.format(i, s) for i, s in enumerate(self.source()))
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.