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 values(cls, dataset, dim, expanded=True, flat=True, compute=True,
               keep_index=False):
        dim = dataset.get_dimension(dim, strict=True)
        data = dataset.data[dim.name]
        if not expanded:
            data = data.unique()
            return data.values_host if compute else data.values
        elif keep_index:
            return data
        elif compute:
            return data.values_host
        try:
            return data.values
        except Exception:
            return data.values_host