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 test_initializers(self):
        class Person(Structure):
            _fields_ = [("name", c_char*6),
                        ("age", c_int)]

        self.assertRaises(TypeError, Person, 42)
        self.assertRaises(ValueError, Person, b"asldkjaslkdjaslkdj")
        self.assertRaises(TypeError, Person, "Name", "HI")

        # short enough
        self.assertEqual(Person(b"12345", 5).name, b"12345")
        # exact fit
        self.assertEqual(Person(b"123456", 5).name, b"123456")
        # too long
        self.assertRaises(ValueError, Person, b"1234567", 5)