Example of the API breakage:

```
/opt/python/3.8-dev/lib/python3.8/pdb.py:321: in _cmdloop
    self.cmdloop()
/opt/python/3.8-dev/lib/python3.8/cmd.py:138: in cmdloop
    stop = self.onecmd(line)
/opt/python/3.8-dev/lib/python3.8/pdb.py:418: in onecmd
    return cmd.Cmd.onecmd(self, line)
/opt/python/3.8-dev/lib/python3.8/cmd.py:217: in onecmd
    return func(arg)
pdb.py:699: in do_debug
    return orig_do_debug(self, cmd)
/opt/python/3.8-dev/lib/python3.8/pdb.py:1097: in do_debug
    code = compile(arg, "<string>", "exec")
E   TypeError: compile() arg 1 must be a string, bytes or AST object
```

(via https://travis-ci.org/antocuni/pdb/jobs/504061679#L367)