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 _exit_with_failure(cls, terminal_msg):
        timestamp_msg = (
            f"timestamp: {cls._iso_timestamp_for_now()}\n"
            if cls._should_print_backtrace_to_terminal
            else ""
        )
        details_msg = (
            ""
            if cls._should_print_backtrace_to_terminal
            else "\n\n(Use --print-exception-stacktrace to see more error details.)"
        )
        terminal_msg = terminal_msg or "<no exit reason provided>"
        formatted_terminal_msg = cls._EXIT_FAILURE_TERMINAL_MESSAGE_FORMAT.format(
            timestamp_msg=timestamp_msg, terminal_msg=terminal_msg, details_msg=details_msg
        )
        # Exit with failure, printing a message to the terminal (or whatever the interactive stream is).
        cls._exiter.exit_and_fail(msg=formatted_terminal_msg, out=cls._interactive_output_stream)