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 _on_item_widget_size_allocate(self, item_widget, allocation, item):
    if item in self._items_allocations:
      self._update_width(allocation.width - self._items_allocations[item].width)
      self._update_height(allocation.height - self._items_allocations[item].height)
    else:
      self._update_width(allocation.width)
      self._update_height(allocation.height + self._item_spacing)