`pdb` CLI doesn't handle incorrect arguments properly

[chgnrdv]

Bug report

Checklist

• I am confident this is a bug in CPython, not a bug in a third-party project
• I have searched the CPython issue tracker,
  and am confident this bug has not been reported before

CPython versions tested on:

3.11, 3.12, CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.13.0a0 (heads/main:578ebc5d5f, Sep 1 2023, 20:48:35) [GCC 10.2.1 20210110]

A clear and concise description of the bug:

pdb module produces large traceback instead of short error message if invoked with invalid command line option. This happens because it doesn't handle exceptions that can occur in getopt.getopt, as it typically done.

$ ./python -m pdb -c
Traceback (most recent call last):
  File "/home/radislav/projects/cpython/Lib/runpy.py", line 198, in _run_module_as_main
    return _run_code(code, main_globals, None,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/runpy.py", line 88, in _run_code
    exec(code, run_globals)
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2114, in <module>
    pdb.main()
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2060, in main
    opts, args = getopt.getopt(sys.argv[1:], 'mhc:', ['help', 'command='])
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/getopt.py", line 95, in getopt
    opts, args = do_shorts(opts, args[0][1:], shortopts, args[1:])
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/getopt.py", line 198, in do_shorts
    raise GetoptError(_('option -%s requires argument') % opt,
getopt.GetoptError: option -c requires argument

A similar situation is with nonexistant modules and directory names. In the first case an exception that occurs in _ModuleTarget.check is printed to stderr with its traceback. In the second case directory name is 'successfully' checked by _ScriptTarget.check call, and debugger is ran on invalid target.

$ ./python -m pdb -m spam
Traceback (most recent call last):
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 166, in check
    self._details
  File "/home/radislav/projects/cpython/Lib/functools.py", line 1014, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 174, in _details
    return runpy._get_module_details(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/runpy.py", line 142, in _get_module_details
    raise error("No module named %s" % mod_name)
ImportError: No module named spam

$ ./python -m pdb /
Traceback (most recent call last):
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2088, in main
    pdb._run(target)
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 1868, in _run
    self.run(target.code)
             ^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 159, in code
    with io.open_code(self) as fp:
         ^^^^^^^^^^^^^^^^^^
IsADirectoryError: [Errno 21] Is a directory: '/'
Uncaught exception. Entering post mortem debugging
Running 'cont' or 'step' will restart the program
> /home/radislav/projects/cpython/Lib/pdb.py(159)code()
-> with io.open_code(self) as fp:
(Pdb) c
Traceback (most recent call last):
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2088, in main
    pdb._run(target)
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 1868, in _run
    self.run(target.code)
             ^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 159, in code
    with io.open_code(self) as fp:
         ^^^^^^^^^^^^^^^^^^
IsADirectoryError: [Errno 21] Is a directory: '/'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/radislav/projects/cpython/Lib/runpy.py", line 198, in _run_module_as_main
    return _run_code(code, main_globals, None,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/runpy.py", line 88, in _run_code
    exec(code, run_globals)
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2114, in <module>
    pdb.main()
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 2106, in main
    pdb.interaction(None, e)
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 501, in interaction
    self._cmdloop()
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 405, in _cmdloop
    self.cmdloop()
  File "/home/radislav/projects/cpython/Lib/cmd.py", line 138, in cmdloop
    stop = self.onecmd(line)
           ^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 592, in onecmd
    return cmd.Cmd.onecmd(self, line)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/cmd.py", line 217, in onecmd
    return func(arg)
           ^^^^^^^^^
  File "/home/radislav/projects/cpython/Lib/pdb.py", line 1329, in do_continue
    self.set_continue()
  File "/home/radislav/projects/cpython/Lib/bdb.py", line 344, in set_continue
    self._set_stopinfo(self.botframe, None, -1)
                       ^^^^^^^^^^^^^
AttributeError: 'Pdb' object has no attribute 'botframe'. Did you mean: 'curframe'?

I'm working on a fix.

Linked PRs

• gh-108791: Fix pdb CLI invalid argument handling #108816
• [3.12] gh-108791: Fix pdb CLI invalid argument handling (GH-108816) #110915
• [3.11] gh-108791: Fix pdb CLI invalid argument handling (GH-108816) #110916
• [3.11] gh-108791: Fix pdb CLI invalid argument handling (GH-108816) #111063
• [3.12] gh-108791: Fix pdb CLI invalid argument handling (GH-108816) #111064