Add a new "python-interactive" command that starts a standard

Python interactive prompt with "pi" as alias, and add "py" as
	an alias to "python".
	* NEWS: Mention the new commands.
	* doc/gdb.texinfo (Python Commands): Document the new
	commands.
	* python/python.c (eval_python_command): New function.
	(python_interactive_command): For "python-interactive" with
	arguments, call eval_python_command.  For "python-interactive"
	without arguments, call PyRun_InteractiveLoop.
	(_initialize_python): Add "python-interactive" command with
	"pi" as alias, and add "py" as an alias to "python".

gdb/ChangeLog

@@ -1,3 +1,18 @@
+2012-08-22  Khoo Yit Phang <khooyp@cs.umd.edu>
+
+	Add a new "python-interactive" command that starts a standard
+	Python interactive prompt with "pi" as alias, and add "py" as
+	an alias to "python".
+	* NEWS: Mention the new commands.
+	* doc/gdb.texinfo (Python Commands): Document the new
+	commands.
+	* python/python.c (eval_python_command): New function.
+	(python_interactive_command): For "python-interactive" with
+	arguments, call eval_python_command.  For "python-interactive"
+	without arguments, call PyRun_InteractiveLoop.
+	(_initialize_python): Add "python-interactive" command with
+	"pi" as alias, and add "py" as an alias to "python".
+
 2012-08-22  Tom Tromey  <tromey@redhat.com>
 
 	* defs.h (quit_flag): Don't declare.

gdb/NEWS

@@ -31,6 +31,14 @@
 maint info bfds
   List the BFDs known to GDB.
 
+python-interactive [command]
+pi [command]
+  Start a Python interactive prompt, or evaluate the optional command
+  and print the result of expressions.
+
+py [command]
+  "py" is a new alias for "python".
+
 * MI changes
 
   ** Command parameter changes are now notified using new async record

gdb/doc/gdb.texinfo

@@ -22506,12 +22506,30 @@ automatically imported when @value{GDBN} starts.
 @cindex python commands
 @cindex commands to access python
 
-@value{GDBN} provides one command for accessing the Python interpreter,
+@value{GDBN} provides two commands for accessing the Python interpreter,
 and one related setting:
 
 @table @code
+@kindex python-interactive
+@kindex pi
+@item python-interactive @r{[}@var{command}@r{]}
+@itemx pi @r{[}@var{command}@r{]}
+Without an argument, the @code{python-interactive} command can be used
+to start an interactive Python prompt.
+
+Alternatively, a single-line Python command can be given as an
+argument and evaluated.  If the command is an expression, the result
+will be printed; otherwise, nothing will be printed.  For example:
+
+@smallexample
+(@value{GDBP}) python-interactive 2 + 3
+5
+@end smallexample
+
 @kindex python
-@item python @r{[}@var{code}@r{]}
+@kindex py
+@item python @r{[}@var{command}@r{]}
+@itemx py @r{[}@var{command}@r{]}
 The @code{python} command can be used to evaluate Python code.
 
 If given an argument, the @code{python} command will evaluate the

gdb/python/python.c

@@ -176,6 +176,75 @@ check_quit_flag (void)
   return PyOS_InterruptOccurred ();
 }
 
+/* Evaluate a Python command like PyRun_SimpleString, but uses
+   Py_single_input which prints the result of expressions, and does
+   not automatically print the stack on errors.  */
+
+static int
+eval_python_command (const char *command)
+{
+  PyObject *m, *d, *v;
+
+  m = PyImport_AddModule ("__main__");
+  if (m == NULL)
+    return -1;
+
+  d = PyModule_GetDict (m);
+  if (d == NULL)
+    return -1;
+  v = PyRun_StringFlags (command, Py_single_input, d, d, NULL);
+  if (v == NULL)
+    return -1;
+
+  Py_DECREF (v);
+  if (Py_FlushLine ())
+    PyErr_Clear ();
+
+  return 0;
+}
+
+/* Implementation of the gdb "python-interactive" command.  */
+
+static void
+python_interactive_command (char *arg, int from_tty)
+{
+  struct cleanup *cleanup;
+  int err;
+
+  cleanup = make_cleanup_restore_integer (&interpreter_async);
+  interpreter_async = 0;
+
+  while (arg && *arg && isspace (*arg))
+    ++arg;
+
+  ensure_python_env (get_current_arch (), current_language);
+
+  if (arg && *arg)
+    {
+      int len = strlen (arg);
+      char *script = xmalloc (len + 2);
+
+      strcpy (script, arg);
+      script[len] = '\n';
+      script[len + 1] = '\0';
+      err = eval_python_command (script);
+      xfree (script);
+    }
+  else
+    {
+      err = PyRun_InteractiveLoop (instream, "<stdin>");
+      dont_repeat ();
+    }
+
+  if (err)
+    {
+      gdbpy_print_stack ();
+      error (_("Error while executing Python code."));
+    }
+
+  do_cleanups (cleanup);
+}
+
 /* A wrapper around PyRun_SimpleFile.  FILE is the Python script to run
    named FILENAME.
 
@@ -1112,10 +1181,11 @@ gdbpy_objfiles (PyObject *unused1, PyObject *unused2)
 
 #else /* HAVE_PYTHON */
 
-/* Dummy implementation of the gdb "python" command.  */
+/* Dummy implementation of the gdb "python-interactive" and "python"
+   command. */
 
 static void
-python_command (char *arg, int from_tty)
+python_interactive_command (char *arg, int from_tty)
 {
   while (arg && *arg && isspace (*arg))
     ++arg;
@@ -1131,6 +1201,12 @@ python_command (char *arg, int from_tty)
     }
 }
 
+static void
+python_command (char *arg, int from_tty)
+{
+  python_interactive_command (arg, from_tty);
+}
+
 void
 eval_python_from_control_command (struct command_line *cmd)
 {
@@ -1197,6 +1273,29 @@ _initialize_python (void)
   char *cmd_name;
   struct cmd_list_element *cmd;
 
+  add_com ("python-interactive", class_obscure,
+	   python_interactive_command,
+#ifdef HAVE_PYTHON
+	   _("\
+Start a Python interactive prompt.\n\
+\n\
+Alternatively, a single-line Python command can be given as an\n\
+argument, and if the command is an expression, the result will be\n\
+printed.  For example:\n\
+\n\
+    (gdb) python-interactive 2 + 3\n\
+    5\n\
+")
+#else /* HAVE_PYTHON */
+	   _("\
+Start a Python interactive prompt.\n\
+\n\
+Python scripting is not supported in this copy of GDB.\n\
+This command is only a placeholder.")
+#endif /* HAVE_PYTHON */
+	   );
+  add_com_alias ("pi", "python-interactive", class_obscure, 1);
+
   add_com ("python", class_obscure, python_command,
 #ifdef HAVE_PYTHON
 	   _("\
@@ -1217,6 +1316,7 @@ Python scripting is not supported in this copy of GDB.\n\
 This command is only a placeholder.")
 #endif /* HAVE_PYTHON */
 	   );
+  add_com_alias ("py", "python", class_obscure, 1);
 
   /* Add set/show python print-stack.  */
   add_prefix_cmd ("python", no_class, user_show_python,