[py3] Ported django.utils.regex_helper.

from __future__ import unicode_literals

from django.utils import six

from django.utils.six.moves import zip

# Mapping of an escape character to a representative of that class. So, e.g.,

# "\w" is replaced by "x" in a reverse URL. A value of None means to ignore

def normalize(pattern):

    """

    Given a reg-exp pattern, normalizes it to a list of forms that suffice for

    reverse matching. This does the following:

    Given a reg-exp pattern, normalizes it to an iterable of forms that

    suffice for reverse matching. This does the following:

    (1) For any repeating sections, keeps the minimum number of occurrences

        permitted (this means zero for optional groups).

    try:

        ch, escaped = next(pattern_iter)

    except StopIteration:

        return zip([''],  [[]])

        return [('', [])]

    try:

        while True:

        pass

    except NotImplementedError:

        # A case of using the disjunctive form. No results for you!

        return zip([''],  [[]])

        return [('', [])]

    return zip(*flatten_result(result))

    return list(zip(*flatten_result(result)))

def next_char(input_iter):

    """