def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def __getitem__(self, key):
        value = self._collection[key]
        if isinstance(key, slice):
            slice_repr = ":".join(str("" if i is None else i) for i in (key.start, key.stop, key.step))
            logger.debug("Get /%s[%s] config key", "/".join(self._path), slice_repr)
            return [self._to_python(item) for item in value]
        else:
            logger.debug("Get /%s[%s] config key", "/".join(self._path), key)
            return self._to_python(value)