def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def check_url_error_message(value):
    try:
        inputs.url(value)
        assert False, u"inputs.url({0}) should raise an exception".format(value)
    except ValueError as e:
        assert_equal(six.text_type(e),
                     (u"{0} is not a valid URL. Did you mean: http://{0}".format(value)))