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 _globpatsplit(pat):
    """Split a glob pattern. Return a list.

    A naive version is "path.split("/")". This function handles more cases, like
    "{*,{a,b}*/*}".

    >>> _globpatsplit("*/**/x/{a,b/c}")
    ['*', '**', 'x', '{a,b/c}']
    """
    result = []
    buf = ""
    parentheses = 0
    for ch in pat:
        if ch == "{":
            parentheses += 1
        elif ch == "}":
            parentheses -= 1
        if parentheses == 0 and ch == "/":
            if buf:
                result.append(buf)
                buf = ""
        else:
            buf += ch
    if buf:
        result.append(buf)
    return result