Python - Why does extend() and append() return None (void)? [duplicate]

Answer 1

I believe the intent was to promote readable code and reduce bugs. This decision was made a very long time ago, but you can probably find more by looking at the archives of the python/python-dev mailing lists.

Python3 would have been the opportunity to change this behaviour, but as you see it remains, so is not considered a design mistake by the development team