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_user_functions():
    x = symbols('x', integer=False)
    n = symbols('n', integer=True)
    custom_functions = {
        "ceiling": "ceil",
        "Abs": [(lambda x: not x.is_integer, "fabs"), (lambda x: x.is_integer, "abs")],
    }
    assert ccode(ceiling(x), user_functions=custom_functions) == "ceil(x)"
    assert ccode(Abs(x), user_functions=custom_functions) == "fabs(x)"
    assert ccode(Abs(n), user_functions=custom_functions) == "abs(n)"