def install_pip(self, package, save=True, save_dev=False):
        """Installs a pip package.

        :param save: if `True`, pins the package to the Hydrogen requirements
            YAML file.
        :param save_dev: if `True`, pins the package as a development
            dependency to the Hydrogen requirements YAML file.
        :param return: a **single** :class:`Requirement` object, representing
            the installed version of the given package.
        """
        requirement = Requirement.coerce(package)
        click.echo("pip install " + requirement.package)
        cmd = envoy.run("pip install {}".format(str(requirement)))
        if cmd.status_code == 0:
            installed_packages = get_installed_pypackages()
            package = installed_packages[requirement.package]
            requirement.version = "=={}".format(package.version)
            if save:
                self.requirements["all"].add(requirement)
            if save_dev:
                self.requirements["dev"].add(requirement)
            if save or save_dev:
                self.requirements.save()
            return requirement
        else:
            fatal(cmd.std_err)
def test_packed(self):
        class X(Structure):
            _fields_ = [("a", c_byte),
                        ("b", c_longlong)]
            _pack_ = 1

        self.assertEqual(sizeof(X), 9)
        self.assertEqual(X.b.offset, 1)

        class X(Structure):
            _fields_ = [("a", c_byte),
                        ("b", c_longlong)]
            _pack_ = 2
        self.assertEqual(sizeof(X), 10)
        self.assertEqual(X.b.offset, 2)

        class X(Structure):
            _fields_ = [("a", c_byte),
                        ("b", c_longlong)]
            _pack_ = 4
        self.assertEqual(sizeof(X), 12)
        self.assertEqual(X.b.offset, 4)

        import struct
        longlong_size = struct.calcsize("q")
        longlong_align = struct.calcsize("bq") - longlong_size

        class X(Structure):
            _fields_ = [("a", c_byte),
                        ("b", c_longlong)]
            _pack_ = 8

        self.assertEqual(sizeof(X), longlong_align + longlong_size)
        self.assertEqual(X.b.offset, min(8, longlong_align))


        d = {"_fields_": [("a", "b"),
                          ("b", "q")],
             "_pack_": -1}
        self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)

        # Issue 15989
        d = {"_fields_": [("a", c_byte)],
             "_pack_": _testcapi.INT_MAX + 1}
        self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)
        d = {"_fields_": [("a", c_byte)],
             "_pack_": _testcapi.UINT_MAX + 2}
        self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)