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 db_version_control(engine, abs_path, version=None):
    """Mark a database as under this repository's version control.

    Once a database is under version control, schema changes should
    only be done via change scripts in this repository.

    :param engine:  SQLAlchemy engine instance for a given database
    :param abs_path: Absolute path to migrate repository
    :param version:  Initial database version
    """
    repository = _find_migrate_repo(abs_path)
    versioning_api.version_control(engine, repository, version)
    return version