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 get_repository_root(cls, location):
        loc = super(Git, cls).get_repository_root(location)
        if loc:
            return loc
        try:
            r = cls.run_command(
                ['rev-parse', '--show-toplevel'],
                cwd=location,
                show_stdout=False,
                stdout_only=True,
                on_returncode='raise',
                log_failed_cmd=False,
            )
        except BadCommand:
            logger.debug("could not determine if %s is under git control "
                         "because git is not available", location)
            return None
        except InstallationError:
            return None
        return os.path.normpath(r.rstrip('\r\n'))