Comment 5 for bug 328805

Hmmm... It's been years and years since Python-mode 1.0alpha was
released, so I suspect you're looking in the wrong place for the version.

We are currently at 4.75. You can get the current python-mode version
by typing

    M-: py-version RET

When I hit M-/ at the place you indicated, it completes with "c12".
I have no idea why it chooses that completion, but it doesn't hang.
It's not obvious to me what it should expand in this context. Did
you have something in mind? If I change the code to

    ...
    a = A('abc')
    a.foo = 12
    a.

when I hit M-/ it properly expands to "a.foo" for me.

Please try upgrading your python-mode.