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 from_mapping(
        self, mapping: t.Optional[t.Mapping[str, t.Any]] = None, **kwargs: t.Any
    ) -> bool:
        """Updates the config like :meth:`update` ignoring items with non-upper
        keys.

        .. versionadded:: 0.11
        """
        mappings: t.Dict[str, t.Any] = {}
        if mapping is not None:
            mappings.update(mapping)
        mappings.update(kwargs)
        for key, value in mappings.items():
            if key.isupper():
                self[key] = value
        return True