Enhance Flask url_for() with optional _strict argument

url_for_ex.py

import re
from flask import url_for
from myflaskapp import app


def url_for_ex(endpoint, **values):
    """Improved version of standard Flask's :func:`url_for`
    that accepts an additional, optional ``_strict`` argument.

    :param _strict: If ``False``, values for the endpoint are not checked
                    for compatibility with types defined in the URL rule.
                    Default: ``True``.
    """
    strict = values.pop('_strict', True)

    if not strict:
        # search for matching URL rule; if that fails, we will just
        # invoke url_for() normally so that Flask can handle the error
        url_arguments = set(key for key in values.iterkeys()
                            if not key.startswith('_'))
        url_rule = None
        for rule in app.url_map.iter_rules(endpoint):
            rule_arguments = set(rule._converters.iterkeys())
            if rule_arguments == url_arguments:
                url_rule = rule.rule
                break

        if url_rule:
            # replace argument placeholders in the URL rule (``<int:foo>``...)
            # with values provided for those arguments
            regex = '|'.join(r'\<(?:\w+\:)?(%s)\>' % arg for arg in values)
            return re.sub(regex, lambda m: str(values[m.group(1)]), url_rule)

    return url_for(endpoint, **values)

app.jinja_env.globals['url_for'] = url_for_ex