pdb: calling registered alias without command raises KeyError #109375
Description
Bug report
Bug description:
pdb allows to register an alias without a command.
Calling that alias raises an unhandled exception.
$ /tmp/ cat bar.py breakpoint() $ /tmp/ python bar.py --Return-- > /tmp/bar.py(1)<module>()->None -> breakpoint() (Pdb) alias foo (Pdb) foo Traceback (most recent call last): File "/tmp/bar.py", line 1, in <module> breakpoint() File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/bdb.py", line 94, in trace_dispatch return self.dispatch_return(frame, arg) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/bdb.py", line 153, in dispatch_return self.user_return(frame, arg) File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/pdb.py", line 372, in user_return self.interaction(frame, None) File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/pdb.py", line 435, in interaction self._cmdloop() File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/pdb.py", line 400, in _cmdloop self.cmdloop() File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/cmd.py", line 137, in cmdloop line = self.precmd(line) ^^^^^^^^^^^^^^^^^ File "/home/home/.pyenv/versions/3.11.1/lib/python3.11/pdb.py", line 473, in precmd while args[0] in self.aliases: ~~~~^^^ IndexError: list index out of rangeThe general syntax of alias foo is valid, as it allows to print the alias. However, if there is no command registered, calling it fails.
I am unsure if raising an exception is the wanted behavior here. I think providing an error message which indicates that the current alias is unknown could be more appropriate, e.g.:
$ python /tmp/bar.py --Return-- > /tmp/bar.py(1)<module>()->None -> breakpoint() (Pdb) alias foo *** Unkown alias. To create an alias see 'help alias'A solution could be to add an additional check to catch cases where one tries to register an alias without a command.
CPython versions tested on:
3.10, 3.11, CPython main branch
Operating systems tested on:
Linux