UserDict -> dict, reasons for migrating existing code

[Andreas Kuntzagk]

Hi,

what would be the reasons to migrate existing code from the use of
UserDict() to dict()? (UserString ...) What would be reasons against?
Reasons I can think of:
pro:
- Speed Improvement because of a level of indirection less
- UserDict can become deprecated

con:
- Code not working whith older python
- cost of migrating large codebase

Do you know other reasons?

Andreas