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 _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