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 setup_run_environment(self, env):
        bashrc = self.prefix.etc.bashrc
        try:
            env.extend(EnvironmentModifications.from_sourcing_file(
                bashrc, clean=True
            ))
        except Exception as e:
            msg = 'unexpected error when sourcing OpenFOAM bashrc [{0}]'
            tty.warn(msg.format(str(e)))