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 __getitem__(self, key):
        value = self._collection[key]
        if isinstance(key, slice):
            slice_repr = ":".join(str("" if i is None else i) for i in (key.start, key.stop, key.step))
            logger.debug("Get /%s[%s] config key", "/".join(self._path), slice_repr)
            return [self._to_python(item) for item in value]
        else:
            logger.debug("Get /%s[%s] config key", "/".join(self._path), key)
            return self._to_python(value)