Make the "python" command resemble the standard Python interpreter

[Tom Tromey]

>>>>> "Yit" == Khoo Yit Phang <khooyp@cs.umd.edu> writes:

Yit> I'd like to contribute a patch to improve the "python" command by
Yit> making it resemble the standard Python interpreter in behavior.

Thanks.

Do you have a copyright assignment in place?
If not, contact me off-list and I will get you started.
We need this before we can incorporate this patch.

Yit> For "python" with arguments, this prints the results of expressions,
Yit> e.g., "python 1 + 2" will print "3" (previously, it will not print
Yit> anything).

Did you run the test suite?  I'm curious if this caused any failures.

On balance, I'm ok with this idea, since I don't think we make many
promises about CLI output remaining the same across versions.

Yit> For "python" without arguments, this uses Python's built-in
Yit> interactive loop (PyRun_InteractiveLoop) so that individual
Yit> statements/expressions are immediately evaluated and results of
Yit> expressions are printed.

Sounds nice.

This also seems like it could cause some (spurious) test failures.

Yit> It also hooks GDB's readline wrappers
Yit> (command_line_input) to Python so that line editing and history
Yit> editing works. Additionally, Python's standard readline module is
Yit> stubbed out because it conflicts with GDB's use of readline.

Can you expand more on how it conflicts?

I think it would be better to make it not conflict somehow.

Yit> +  TRY_CATCH (except, RETURN_MASK_ALL)
Yit> +    {
Yit> +      struct cleanup *cleanup = gdbpy_suspend_sigint_handler ();
Yit> +      p = command_line_input (prompt, 0, "python");
Yit> +      do_cleanups (cleanup);
Yit> +    }
Yit> +
Yit> +  /* Detect Ctrl-C and treat as KeyboardInterrupt. */
Yit> +  if (except.reason == RETURN_QUIT)
Yit> +    return NULL;

Does this case need the Python exception to be set?  If not, I think it
would be good to expand this comment to explain the situation.

Yit> +  m = PyImport_AddModule ("__main__");
Yit> +  if (m == NULL)
Yit> +    error (_("Error while executing Python code."));

You have to do something with the Python exception here.
Usually we use gdbpy_print_stack, but sometimes other things are
appropriate.

Yit> +  d = PyModule_GetDict (m);

Do we need error checking?
I didn't look at the API docs.

Yit> +  v = PyRun_StringFlags (command,
Yit> +			 from_tty ? Py_single_input : Py_file_input,
Yit> +			 d, d, NULL);
Yit> +  if (v == NULL)
Yit> +    {
Yit> +      int interrupt = PyErr_ExceptionMatches (PyExc_KeyboardInterrupt);
Yit> +      PyErr_Print ();

gdbpy_print_stack.

Yit> +      if (! interrupt)
Yit> +	error (_("Error while executing Python code."));

Why the special case for interrupts here?

Tom