def load(self, filename, create_if_missing=True):
        filename = Path(filename)
        if not filename.exists() and create_if_missing:
            self.load_pip_requirements()
            with filename.open("w") as f:
                f.write(yaml.dump(self.serialized, default_flow_style=False,
                                  encoding=None))
            self.filename = filename
            return self.save(filename)
        with filename.open() as f:
            for group, requirements in yaml.load(f.read()).items():
                for requirement in requirements:
                    self[group].add(Requirement.coerce(requirement))
        self.filename = filename
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