def on_cleanup_error(function, path, excinfo):
                click.secho("warning: failed to remove file or directory: {}\n"
                            "please delete it manually.".format(path),
                            fg="red")
def pop(self, key, default=None):
        value = self._collection.pop(key, default)
        if isinstance(value, Proxy):
            value = value.get()
        return value