def freeze(h, output_yaml, resolve, groups):
    """Output installed packages."""
    if not groups:
        groups = filter(lambda group: not group.lower().startswith("bower"),
                        h.requirements.keys())
    else:
        groups = [text_type.strip(group) for group in groups.split(",")]

    if output_yaml:
        for requirements in h.requirements.values():
            for requirement in requirements:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
        click.echo(h.requirements.yaml)
    else:
        for group in groups:
            if not h.requirements[group]:
                continue
            click.echo("# {}".format(group))
            for requirement in h.requirements[group]:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
                click.echo(str(requirement))
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)