pythonoperator-overloading

Why does Python have an __ne__ operator method instead of just __eq__?

The answer here gives a handwaving reference to cases where you'd want __ne__ to return something other than just the logical inverse of __eq__, but I can't imagine any such case. Any examples?

Solution

  • SQLAlchemy is a great example. For the uninitiated, SQLAlchemy is a ORM and uses Python expression to generate SQL statements. In a expression such as

    meta.Session.query(model.Theme).filter(model.Theme.id == model.Vote.post_id)

    the model.Theme.id == model.VoteWarn.post_id does not return a boolean, but a object that eventually produces a SQL query like WHERE theme.id = vote.post_id. The inverse would produce something like WHERE theme.id <> vote.post_id so both methods need to be defined.