def __delitem__(self, key):
tpl = '<STR_LIT>'<EOL>raise InvalidOperation(tpl % (key, self))<EOL>
Explicitly prevent deleting data from the object via the `del`
command.

.. code-block:: python

    del user['name']  # raises InvalidOperation exception!

The reason is because I want you to use the `remove` method instead.
That way you can pipeline the removal of the redis field with
something else.

Also, you probably want to avoid a scenario where you accidentally
delete data from redis without meaning to.

:param key: the name of the element to remove from the dict.
:raise: InvalidOperation