A simple example...

If I create a directory hierarchy like this:

./xyzzy
./xyzzy/__init__.py
./xyzzy/plugh
./xyzzy/plugh/__init__.py
./xyzzy/plugh/bar.py
./xyzzy/plugh/foo.py

Running bpython using python2.7.16 will successfully autocomplete "foo" and "bar", e.g. "from xyzzy.plugh." will show "foo" and "bar" in the autocomplete box. However, running bpython using python3.7.3 it will only autocomplete "xyzzy" or "xyzzy.plugh" (which are packages/directories), while "foo" and "bar" are modules/files.