def load(self, filename, create_if_missing=True):
        filename = Path(filename)
        if not filename.exists() and create_if_missing:
            self.load_pip_requirements()
            with filename.open("w") as f:
                f.write(yaml.dump(self.serialized, default_flow_style=False,
                                  encoding=None))
            self.filename = filename
            return self.save(filename)
        with filename.open() as f:
            for group, requirements in yaml.load(f.read()).items():
                for requirement in requirements:
                    self[group].add(Requirement.coerce(requirement))
        self.filename = filename
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))