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_ccode_Rational():
    assert ccode(Rational(3, 7)) == "3.0L/7.0L"
    assert ccode(Rational(18, 9)) == "2"
    assert ccode(Rational(3, -7)) == "-3.0L/7.0L"
    assert ccode(Rational(-3, -7)) == "3.0L/7.0L"
    assert ccode(x + Rational(3, 7)) == "x + 3.0L/7.0L"
    assert ccode(Rational(3, 7)*x) == "(3.0L/7.0L)*x"