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_pre_update_validate_complains_if_nothing_changed(self):
        change = {
            'cmd': question_domain.CMD_CREATE_NEW_FULLY_SPECIFIED_QUESTION,
            'question_dict': {
                'question_state_data': self._create_valid_question_data(
                    'default_state').to_dict(),
                'language_code': 'en',
                'question_state_data_schema_version': (
                    feconf.CURRENT_STATE_SCHEMA_VERSION)
            },
            'skill_id': 'skill_1',
            'skill_difficulty': 0.3
        }

        suggestion = suggestion_registry.SuggestionAddQuestion(
            'exploration.exp1.thread1', 'exp1', 1,
            suggestion_models.STATUS_ACCEPTED, self.author_id,
            self.reviewer_id, change,
            'question.topic_1', 'en', self.fake_date)

        new_change = {
            'cmd': question_domain.CMD_CREATE_NEW_FULLY_SPECIFIED_QUESTION,
            'question_dict': {
                'question_state_data': self._create_valid_question_data(
                    'default_state').to_dict(),
                'language_code': 'en',
                'question_state_data_schema_version': (
                    feconf.CURRENT_STATE_SCHEMA_VERSION)
            },
            'skill_id': 'skill_1',
            'skill_difficulty': 0.3
        }

        with self.assertRaisesRegex(
            utils.ValidationError,
            'At least one of the new skill_difficulty or question_dict '
            'should be changed.'):
            suggestion.pre_update_validate(
                question_domain.QuestionSuggestionChange(new_change))