I would recommend to not use BaseException, but simply Exception here. Otherwise there is still a small race condition, e.g. if there is some KeyboardInterrupt after _io.open already created the file instance. Then you would run exactly in the same problem as before, that os.close is called twice.

I don't understand the bad scenario you are describing. If there is a KeyboardInterrupt, then BaseException will catch it, and either the first or the second except clause will handle it (depending on exactly when the Ctrl-C happens), and the objects will be freed.

If we change to Exception, then KeyboardInterrupts won't be caught at all, and none of the clean up will happen.

The bytecode will look sth like:

  2           0 SETUP_EXCEPT            14 (to 16)

  3           2 LOAD_GLOBAL              0 (_io)
              4 LOAD_METHOD              1 (open)
              6 LOAD_FAST                0 (fd)
             ... (other args ignored here)
              8 CALL_METHOD              1
             ... assume KeyboardInterrupt is catched exactly here
             10 STORE_FAST               1 (file)
             12 POP_BLOCK
             14 JUMP_FORWARD            30 (to 46)

  4     >>   16 DUP_TOP
             18 LOAD_GLOBAL              2 (BaseException)
             20 COMPARE_OP              10 (exception match)
             22 POP_JUMP_IF_FALSE       44
             24 POP_TOP
             26 POP_TOP
             28 POP_TOP
             ...

It means that the file object already exists, and once the GC cleans it up, that file object will close the fd. However, now our exception handler runs, and also calls os.close(fd) again.

Also here, better Exception instead of BaseException.