def __init__(self, package, version):
        """Construct a new requirement.

        :param package: the package name.
        :param version: a semver compatible version specification.
        """
        self.package = package
        self.version = version
        if self.version and not re.match(r"[<=>~]", version[:2]):
            self.version = "=={}".format(self.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)