def load_installed_version(self):
        installed_packages = get_installed_pypackages()
        if self.package in installed_packages:
            self.version = "=={}".format(
                installed_packages[self.package].version)
def test_exceptions(self):
        self.assert_(issubclass(DeoptionError, TypeError))
        self.assertRaises(TypeError,
            lambda: Optional()
        )
        self.assertRaises(TypeError,
            lambda: Optional(NotPassed, NotPassed)
        )