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 log_stream(self, logger_name, level_name, format_str):
        """ Attaches a log handler to the specified logger and sends emitted logs 
            back as stream. 
        """
        if logger_name != "" and logger_name not in self.available_loggers():
            raise ValueError("logger {0} is not available".format(logger_name))

        level_name_upper = level_name.upper() if level_name else "NOTSET"
        try:
            level = getattr(logging, level_name_upper)
        except AttributeError, e:
            raise AttributeError("log level {0} is not available".format(level_name_upper))