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 _convertretoglobs(repat):
    """Attempt to convert a regular expression pattern to glob patterns.

    A single regular expression pattern might be converted into multiple
    glob patterns.

    Return None if conversion is unsupported.

    >>> _convertretoglobs("abc*") is None
    True
    >>> _convertretoglobs("xx/yy/(?!zz/kk)")
    ['xx/yy/**', '!xx/yy/zz/kk/**']
    >>> _convertretoglobs("x/y/(?:.*/)?BUCK")
    ['x/y/**/BUCK']
    """
    m = _repat1.match(repat)
    if m:
        prefix, excluded = m.groups()
        return ["%s/**" % prefix, "!%s/%s/**" % (prefix, excluded)]
    m = _repat2.match(repat)
    if m:
        prefix, name = m.groups()
        return ["%s/**/%s" % (prefix, name)]
    return None