What kind of feature are you missing? Where do you notice a shortcoming of PTB?

When using persistent chat_data, there's no method for purging entries which have been emptied. The chat_id key will always remain in the chat_data defaultdict. I believe it's the same for user_data.

Because of the Dispatcher.__update_persistence() implementation, even deleting the keys with del chat_data[k] won't remove them from the persistence file. See:

Describe the solution you'd like

• Add a method to the Dispatcher class for removing a key from the persistence file, with the key as parameter. It should not matter to the method whether the related value is empty or not.
• Add another method for purging all orphaned keys from the persistence file.

There probably should be 4 methods, 2 for chat_data and 2 for user_data.

Describe alternatives you've considered

No response

Additional context

No response