def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def wait_for_snapshot_status(self, snapshot_id, status):
        """Waits for a Snapshot to reach a given status."""
        start_time = time.time()
        old_value = value = self._get_snapshot_status(snapshot_id)
        while True:
            dtime = time.time() - start_time
            time.sleep(self.build_interval)
            if value != old_value:
                LOG.info('Value transition from "%s" to "%s"'
                         'in %d second(s).', old_value,
                         value, dtime)
            if (value == status):
                return value

            if dtime > self.build_timeout:
                message = ('Time Limit Exceeded! (%ds)'
                           'while waiting for %s, '
                           'but we got %s.' %
                           (self.build_timeout, status, value))
                raise exceptions.TimeoutException(message)
            time.sleep(self.build_interval)
            old_value = value
            value = self._get_snapshot_status(snapshot_id)