gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008, 2009, 2010 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "exceptions.h"
  22 #include "objfiles.h"
  23 #include "symtab.h"
  24 #include "language.h"
  25 #include "valprint.h"
  26
  27 #include "python.h"
  28
  29 #ifdef HAVE_PYTHON
  30 #include "python-internal.h"
  31
  32 /* Return type of print_string_repr.  */
  33
  34 enum string_repr_result
  35   {
  36     /* The string method returned None.  */
  37     string_repr_none,
  38     /* The string method had an error.  */
  39     string_repr_error,
  40     /* Everything ok.  */
  41     string_repr_ok
  42   };
  43
  44 /* Helper function for find_pretty_printer which iterates over a list,
  45    calls each function and inspects output.  This will return a
  46    printer object if one recognizes VALUE.  If no printer is found, it
  47    will return None.  On error, it will set the Python error and
  48    return NULL.  */
  49
  50 static PyObject *
  51 search_pp_list (PyObject *list, PyObject *value)
  52 {
  53   Py_ssize_t pp_list_size, list_index;
  54   PyObject *function, *printer = NULL;
  55
  56   pp_list_size = PyList_Size (list);
  57   for (list_index = 0; list_index < pp_list_size; list_index++)
  58     {
  59       function = PyList_GetItem (list, list_index);
  60       if (! function)
  61         return NULL;
  62
  63       /* Skip if disabled.  */
  64       if (PyObject_HasAttr (function, gdbpy_enabled_cst))
  65         {
  66           PyObject *attr = PyObject_GetAttr (function, gdbpy_enabled_cst);
  67           int cmp;
  68
  69           if (!attr)
  70             return NULL;
  71           cmp = PyObject_IsTrue (attr);
  72           if (cmp == -1)
  73             return NULL;
  74
  75           if (!cmp)
  76             continue;
  77         }
  78
  79       printer = PyObject_CallFunctionObjArgs (function, value, NULL);
  80       if (! printer)
  81         return NULL;
  82       else if (printer != Py_None)
  83         return printer;
  84
  85       Py_DECREF (printer);
  86     }
  87
  88   Py_RETURN_NONE;
  89 }
  90
  91 /* Subroutine of find_pretty_printer to simplify it.
  92    Look for a pretty-printer to print VALUE in all objfiles.
  93    The result is NULL if there's an error and the search should be terminated.
  94    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
  95    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
  96
  97 static PyObject *
  98 find_pretty_printer_from_objfiles (PyObject *value)
  99 {
 100   PyObject *pp_list;
 101   PyObject *function;
 102   struct objfile *obj;
 103
 104   ALL_OBJFILES (obj)
 105   {
 106     PyObject *objf = objfile_to_objfile_object (obj);
 107     if (!objf)
 108       {
 109         /* Ignore the error and continue.  */
 110         PyErr_Clear ();
 111         continue;
 112       }
 113
 114     pp_list = objfpy_get_printers (objf, NULL);
 115     function = search_pp_list (pp_list, value);
 116     Py_XDECREF (pp_list);
 117
 118     /* If there is an error in any objfile list, abort the search and exit.  */
 119     if (! function)
 120       return NULL;
 121
 122     if (function != Py_None)
 123       return function;
 124
 125     Py_DECREF (function);
 126   }
 127
 128   Py_RETURN_NONE;
 129 }
 130
 131 /* Subroutine of find_pretty_printer to simplify it.
 132    Look for a pretty-printer to print VALUE in the current program space.
 133    The result is NULL if there's an error and the search should be terminated.
 134    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 135    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 136
 137 static PyObject *
 138 find_pretty_printer_from_progspace (PyObject *value)
 139 {
 140   PyObject *pp_list;
 141   PyObject *function;
 142   PyObject *obj = pspace_to_pspace_object (current_program_space);
 143
 144   if (!obj)
 145     return NULL;
 146   pp_list = pspy_get_printers (obj, NULL);
 147   function = search_pp_list (pp_list, value);
 148   Py_XDECREF (pp_list);
 149   return function;
 150 }
 151
 152 /* Subroutine of find_pretty_printer to simplify it.
 153    Look for a pretty-printer to print VALUE in the gdb module.
 154    The result is NULL if there's an error and the search should be terminated.
 155    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 156    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 157
 158 static PyObject *
 159 find_pretty_printer_from_gdb (PyObject *value)
 160 {
 161   PyObject *pp_list;
 162   PyObject *function;
 163
 164   /* Fetch the global pretty printer list.  */
 165   if (! PyObject_HasAttrString (gdb_module, "pretty_printers"))
 166     Py_RETURN_NONE;
 167   pp_list = PyObject_GetAttrString (gdb_module, "pretty_printers");
 168   if (pp_list == NULL || ! PyList_Check (pp_list))
 169     {
 170       Py_XDECREF (pp_list);
 171       Py_RETURN_NONE;
 172     }
 173
 174   function = search_pp_list (pp_list, value);
 175   Py_XDECREF (pp_list);
 176   return function;
 177 }
 178
 179 /* Find the pretty-printing constructor function for VALUE.  If no
 180    pretty-printer exists, return None.  If one exists, return a new
 181    reference.  On error, set the Python error and return NULL.  */
 182
 183 static PyObject *
 184 find_pretty_printer (PyObject *value)
 185 {
 186   PyObject *function;
 187
 188   /* Look at the pretty-printer list for each objfile
 189      in the current program-space.  */
 190   function = find_pretty_printer_from_objfiles (value);
 191   if (function == NULL || function != Py_None)
 192     return function;
 193   Py_DECREF (function);
 194
 195   /* Look at the pretty-printer list for the current program-space.  */
 196   function = find_pretty_printer_from_progspace (value);
 197   if (function == NULL || function != Py_None)
 198     return function;
 199   Py_DECREF (function);
 200
 201   /* Look at the pretty-printer list in the gdb module.  */
 202   function = find_pretty_printer_from_gdb (value);
 203   return function;
 204 }
 205
 206 /* Pretty-print a single value, via the printer object PRINTER.
 207    If the function returns a string, a PyObject containing the string
 208    is returned.  If the function returns Py_NONE that means the pretty
 209    printer returned the Python None as a value.  Otherwise, if the
 210    function returns a value,  *OUT_VALUE is set to the value, and NULL
 211    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 212    returned, with a python exception set.  */
 213
 214 static PyObject *
 215 pretty_print_one_value (PyObject *printer, struct value **out_value)
 216 {
 217   volatile struct gdb_exception except;
 218   PyObject *result = NULL;
 219
 220   *out_value = NULL;
 221   TRY_CATCH (except, RETURN_MASK_ALL)
 222     {
 223       result = PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst, NULL);
 224       if (result)
 225         {
 226           if (! gdbpy_is_string (result) && ! gdbpy_is_lazy_string (result)
 227               && result != Py_None)
 228             {
 229               *out_value = convert_value_from_python (result);
 230               if (PyErr_Occurred ())
 231                 *out_value = NULL;
 232               Py_DECREF (result);
 233               result = NULL;
 234             }
 235         }
 236     }
 237
 238   return result;
 239 }
 240
 241 /* Return the display hint for the object printer, PRINTER.  Return
 242    NULL if there is no display_hint method, or if the method did not
 243    return a string.  On error, print stack trace and return NULL.  On
 244    success, return an xmalloc()d string.  */
 245 char *
 246 gdbpy_get_display_hint (PyObject *printer)
 247 {
 248   PyObject *hint;
 249   char *result = NULL;
 250
 251   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 252     return NULL;
 253
 254   hint = PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst, NULL);
 255   if (hint)
 256     {
 257       if (gdbpy_is_string (hint))
 258         {
 259           result = python_string_to_host_string (hint);
 260           if (result == NULL)
 261             gdbpy_print_stack ();
 262         }
 263       Py_DECREF (hint);
 264     }
 265   else
 266     gdbpy_print_stack ();
 267
 268   return result;
 269 }
 270
 271 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 272
 273 static void
 274 print_stack_unless_memory_error (struct ui_file *stream)
 275 {
 276   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 277     {
 278       struct cleanup *cleanup;
 279       PyObject *type, *value, *trace;
 280       char *msg;
 281
 282       PyErr_Fetch (&type, &value, &trace);
 283       cleanup = make_cleanup_py_decref (type);
 284       make_cleanup_py_decref (value);
 285       make_cleanup_py_decref (trace);
 286
 287       msg = gdbpy_exception_to_string (type, value);
 288       make_cleanup (xfree, msg);
 289
 290       if (msg == NULL || *msg == '\0')
 291         fprintf_filtered (stream, _("<error reading variable"));
 292       else
 293         fprintf_filtered (stream, _("<error reading variable: %s>"), msg);
 294
 295       do_cleanups (cleanup);
 296     }
 297   else
 298     gdbpy_print_stack ();
 299 }
 300
 301 /* Helper for apply_val_pretty_printer which calls to_string and
 302    formats the result.  */
 303
 304 static enum string_repr_result
 305 print_string_repr (PyObject *printer, const char *hint,
 306                    struct ui_file *stream, int recurse,
 307                    const struct value_print_options *options,
 308                    const struct language_defn *language,
 309                    struct gdbarch *gdbarch)
 310 {
 311   struct value *replacement = NULL;
 312   PyObject *py_str = NULL;
 313   enum string_repr_result result = string_repr_ok;
 314
 315   py_str = pretty_print_one_value (printer, &replacement);
 316   if (py_str)
 317     {
 318       struct cleanup *cleanup = make_cleanup_py_decref (py_str);
 319
 320       if (py_str == Py_None)
 321         result = string_repr_none;
 322       else if (gdbpy_is_lazy_string (py_str))
 323         {
 324           CORE_ADDR addr;
 325           long length;
 326           struct type *type;
 327           char *encoding = NULL;
 328
 329           make_cleanup (free_current_contents, &encoding);
 330           gdbpy_extract_lazy_string (py_str, &addr, &type,
 331                                      &length, &encoding);
 332
 333           val_print_string (type, encoding, addr, (int) length,
 334                             stream, options);
 335         }
 336       else
 337         {
 338           PyObject *string;
 339
 340           string = python_string_to_target_python_string (py_str);
 341           if (string)
 342             {
 343               gdb_byte *output;
 344               long length;
 345               struct type *type;
 346
 347               make_cleanup_py_decref (string);
 348               output = PyString_AsString (string);
 349               length = PyString_Size (string);
 350               type = builtin_type (gdbarch)->builtin_char;
 351
 352               if (hint && !strcmp (hint, "string"))
 353                 LA_PRINT_STRING (stream, type, output, length, NULL,
 354                                  0, options);
 355               else
 356                 fputs_filtered (output, stream);
 357             }
 358           else
 359             {
 360               result = string_repr_error;
 361               print_stack_unless_memory_error (stream);
 362             }
 363         }
 364
 365       do_cleanups (cleanup);
 366     }
 367   else if (replacement)
 368     {
 369       struct value_print_options opts = *options;
 370
 371       opts.addressprint = 0;
 372       common_val_print (replacement, stream, recurse, &opts, language);
 373     }
 374   else
 375     {
 376       result = string_repr_error;
 377       print_stack_unless_memory_error (stream);
 378     }
 379
 380   return result;
 381 }
 382
 383 static void
 384 py_restore_tstate (void *p)
 385 {
 386   PyFrameObject *frame = p;
 387   PyThreadState *tstate = PyThreadState_GET ();
 388
 389   tstate->frame = frame;
 390 }
 391
 392 /* Create a dummy PyFrameObject, needed to work around
 393    a Python-2.4 bug with generators.  */
 394 static PyObject *
 395 push_dummy_python_frame ()
 396 {
 397   PyObject *empty_string, *null_tuple, *globals;
 398   PyCodeObject *code;
 399   PyFrameObject *frame;
 400   PyThreadState *tstate;
 401
 402   empty_string = PyString_FromString ("");
 403   if (!empty_string)
 404     return NULL;
 405
 406   null_tuple = PyTuple_New (0);
 407   if (!null_tuple)
 408     {
 409       Py_DECREF (empty_string);
 410       return NULL;
 411     }
 412
 413   code = PyCode_New (0,                 /* argcount */
 414                      0,                 /* nlocals */
 415                      0,                 /* stacksize */
 416                      0,                 /* flags */
 417                      empty_string,      /* code */
 418                      null_tuple,        /* consts */
 419                      null_tuple,        /* names */
 420                      null_tuple,        /* varnames */
 421 #if PYTHON_API_VERSION >= 1010
 422                      null_tuple,        /* freevars */
 423                      null_tuple,        /* cellvars */
 424 #endif
 425                      empty_string,      /* filename */
 426                      empty_string,      /* name */
 427                      1,                 /* firstlineno */
 428                      empty_string       /* lnotab */
 429                     );
 430
 431   Py_DECREF (empty_string);
 432   Py_DECREF (null_tuple);
 433
 434   if (!code)
 435     return NULL;
 436
 437   globals = PyDict_New ();
 438   if (!globals)
 439     {
 440       Py_DECREF (code);
 441       return NULL;
 442     }
 443
 444   tstate = PyThreadState_GET ();
 445
 446   frame = PyFrame_New (tstate, code, globals, NULL);
 447
 448   Py_DECREF (globals);
 449   Py_DECREF (code);
 450
 451   if (!frame)
 452     return NULL;
 453
 454   tstate->frame = frame;
 455   make_cleanup (py_restore_tstate, frame->f_back);
 456   return (PyObject *) frame;
 457 }
 458
 459 /* Helper for apply_val_pretty_printer that formats children of the
 460    printer, if any exist.  If is_py_none is true, then nothing has
 461    been printed by to_string, and format output accordingly. */
 462 static void
 463 print_children (PyObject *printer, const char *hint,
 464                 struct ui_file *stream, int recurse,
 465                 const struct value_print_options *options,
 466                 const struct language_defn *language,
 467                 int is_py_none)
 468 {
 469   int is_map, is_array, done_flag, pretty;
 470   unsigned int i;
 471   PyObject *children, *iter, *frame;
 472   struct cleanup *cleanups;
 473
 474   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 475     return;
 476
 477   /* If we are printing a map or an array, we want some special
 478      formatting.  */
 479   is_map = hint && ! strcmp (hint, "map");
 480   is_array = hint && ! strcmp (hint, "array");
 481
 482   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 483                                          NULL);
 484   if (! children)
 485     {
 486       print_stack_unless_memory_error (stream);
 487       return;
 488     }
 489
 490   cleanups = make_cleanup_py_decref (children);
 491
 492   iter = PyObject_GetIter (children);
 493   if (!iter)
 494     {
 495       print_stack_unless_memory_error (stream);
 496       goto done;
 497     }
 498   make_cleanup_py_decref (iter);
 499
 500   /* Use the prettyprint_arrays option if we are printing an array,
 501      and the pretty option otherwise.  */
 502   pretty = is_array ? options->prettyprint_arrays : options->pretty;
 503
 504   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 505      where it insists on having a non-NULL tstate->frame when
 506      a generator is called.  */
 507   frame = push_dummy_python_frame ();
 508   if (!frame)
 509     {
 510       gdbpy_print_stack ();
 511       goto done;
 512     }
 513   make_cleanup_py_decref (frame);
 514
 515   done_flag = 0;
 516   for (i = 0; i < options->print_max; ++i)
 517     {
 518       PyObject *py_v, *item = PyIter_Next (iter);
 519       char *name;
 520       struct cleanup *inner_cleanup;
 521
 522       if (! item)
 523         {
 524           if (PyErr_Occurred ())
 525             print_stack_unless_memory_error (stream);
 526           /* Set a flag so we can know whether we printed all the
 527              available elements.  */
 528           else
 529             done_flag = 1;
 530           break;
 531         }
 532
 533       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 534         {
 535           gdbpy_print_stack ();
 536           Py_DECREF (item);
 537           continue;
 538         }
 539       inner_cleanup = make_cleanup_py_decref (item);
 540
 541       /* Print initial "{".  For other elements, there are three
 542          cases:
 543          1. Maps.  Print a "," after each value element.
 544          2. Arrays.  Always print a ",".
 545          3. Other.  Always print a ",".  */
 546       if (i == 0)
 547         {
 548          if (is_py_none)
 549            fputs_filtered ("{", stream);
 550          else
 551            fputs_filtered (" = {", stream);
 552        }
 553
 554       else if (! is_map || i % 2 == 0)
 555         fputs_filtered (pretty ? "," : ", ", stream);
 556
 557       /* In summary mode, we just want to print "= {...}" if there is
 558          a value.  */
 559       if (options->summary)
 560         {
 561           /* This increment tricks the post-loop logic to print what
 562              we want.  */
 563           ++i;
 564           /* Likewise.  */
 565           pretty = 0;
 566           break;
 567         }
 568
 569       if (! is_map || i % 2 == 0)
 570         {
 571           if (pretty)
 572             {
 573               fputs_filtered ("\n", stream);
 574               print_spaces_filtered (2 + 2 * recurse, stream);
 575             }
 576           else
 577             wrap_here (n_spaces (2 + 2 *recurse));
 578         }
 579
 580       if (is_map && i % 2 == 0)
 581         fputs_filtered ("[", stream);
 582       else if (is_array)
 583         {
 584           /* We print the index, not whatever the child method
 585              returned as the name.  */
 586           if (options->print_array_indexes)
 587             fprintf_filtered (stream, "[%d] = ", i);
 588         }
 589       else if (! is_map)
 590         {
 591           fputs_filtered (name, stream);
 592           fputs_filtered (" = ", stream);
 593         }
 594
 595       if (gdbpy_is_lazy_string (py_v))
 596         {
 597           CORE_ADDR addr;
 598           struct type *type;
 599           long length;
 600           char *encoding = NULL;
 601
 602           make_cleanup (free_current_contents, &encoding);
 603           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 604
 605           val_print_string (type, encoding, addr, (int) length, stream,
 606                             options);
 607
 608           do_cleanups (inner_cleanup);
 609         }
 610       else if (gdbpy_is_string (py_v))
 611         {
 612           gdb_byte *output;
 613
 614           output = python_string_to_host_string (py_v);
 615           if (!output)
 616             gdbpy_print_stack ();
 617           else
 618             {
 619               fputs_filtered (output, stream);
 620               xfree (output);
 621             }
 622         }
 623       else
 624         {
 625           struct value *value = convert_value_from_python (py_v);
 626
 627           if (value == NULL)
 628             {
 629               gdbpy_print_stack ();
 630               error (_("Error while executing Python code."));
 631             }
 632           else
 633             common_val_print (value, stream, recurse + 1, options, language);
 634         }
 635
 636       if (is_map && i % 2 == 0)
 637         fputs_filtered ("] = ", stream);
 638
 639       do_cleanups (inner_cleanup);
 640     }
 641
 642   if (i)
 643     {
 644       if (!done_flag)
 645         {
 646           if (pretty)
 647             {
 648               fputs_filtered ("\n", stream);
 649               print_spaces_filtered (2 + 2 * recurse, stream);
 650             }
 651           fputs_filtered ("...", stream);
 652         }
 653       if (pretty)
 654         {
 655           fputs_filtered ("\n", stream);
 656           print_spaces_filtered (2 * recurse, stream);
 657         }
 658       fputs_filtered ("}", stream);
 659     }
 660
 661  done:
 662   do_cleanups (cleanups);
 663 }
 664
 665 int
 666 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 667                           int embedded_offset, CORE_ADDR address,
 668                           struct ui_file *stream, int recurse,
 669                           const struct value *val,
 670                           const struct value_print_options *options,
 671                           const struct language_defn *language)
 672 {
 673   struct gdbarch *gdbarch = get_type_arch (type);
 674   PyObject *printer = NULL;
 675   PyObject *val_obj = NULL;
 676   struct value *value;
 677   char *hint = NULL;
 678   struct cleanup *cleanups;
 679   int result = 0;
 680   enum string_repr_result print_result;
 681   cleanups = ensure_python_env (gdbarch, language);
 682
 683   /* Instantiate the printer.  */
 684   if (valaddr)
 685     valaddr += embedded_offset;
 686   value = value_from_contents_and_address (type, valaddr,
 687                                            address + embedded_offset);
 688   if (val != NULL)
 689     {
 690       set_value_component_location (value, val);
 691       /* set_value_component_location resets the address, so we may
 692          need to set it again.  */
 693       if (VALUE_LVAL (value) != lval_internalvar
 694           && VALUE_LVAL (value) != lval_internalvar_component
 695           && VALUE_LVAL (value) != lval_computed)
 696         set_value_address (value, address + embedded_offset);
 697     }
 698
 699   val_obj = value_to_value_object (value);
 700   if (! val_obj)
 701     goto done;
 702
 703   /* Find the constructor.  */
 704   printer = find_pretty_printer (val_obj);
 705   Py_DECREF (val_obj);
 706   make_cleanup_py_decref (printer);
 707   if (! printer || printer == Py_None)
 708     goto done;
 709
 710   /* If we are printing a map, we want some special formatting.  */
 711   hint = gdbpy_get_display_hint (printer);
 712   make_cleanup (free_current_contents, &hint);
 713
 714   /* Print the section */
 715   print_result = print_string_repr (printer, hint, stream, recurse,
 716                                     options, language, gdbarch);
 717   if (print_result != string_repr_error)
 718     print_children (printer, hint, stream, recurse, options, language,
 719                     print_result == string_repr_none);
 720
 721   result = 1;
 722
 723
 724  done:
 725   if (PyErr_Occurred ())
 726     print_stack_unless_memory_error (stream);
 727   do_cleanups (cleanups);
 728   return result;
 729 }
 730
 731
 732 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 733    print object.  It must have a 'to_string' method (but this is
 734    checked by varobj, not here) which takes no arguments and
 735    returns a string.  The printer will return a value and in the case
 736    of a Python string being returned, this function will return a
 737    PyObject containing the string.  For any other type, *REPLACEMENT is
 738    set to the replacement value and this function returns NULL.  On
 739    error, *REPLACEMENT is set to NULL and this function also returns
 740    NULL.  */
 741 PyObject *
 742 apply_varobj_pretty_printer (PyObject *printer_obj,
 743                              struct value **replacement,
 744                              struct ui_file *stream)
 745 {
 746   PyObject *py_str = NULL;
 747
 748   *replacement = NULL;
 749   py_str = pretty_print_one_value (printer_obj, replacement);
 750
 751   if (*replacement == NULL && py_str == NULL)
 752     print_stack_unless_memory_error (stream);
 753
 754   return py_str;
 755 }
 756
 757 /* Find a pretty-printer object for the varobj module.  Returns a new
 758    reference to the object if successful; returns NULL if not.  VALUE
 759    is the value for which a printer tests to determine if it
 760    can pretty-print the value.  */
 761 PyObject *
 762 gdbpy_get_varobj_pretty_printer (struct value *value)
 763 {
 764   PyObject *val_obj;
 765   PyObject *pretty_printer = NULL;
 766   volatile struct gdb_exception except;
 767
 768   TRY_CATCH (except, RETURN_MASK_ALL)
 769     {
 770       value = value_copy (value);
 771     }
 772   GDB_PY_HANDLE_EXCEPTION (except);
 773
 774   val_obj = value_to_value_object (value);
 775   if (! val_obj)
 776     return NULL;
 777
 778   pretty_printer = find_pretty_printer (val_obj);
 779   Py_DECREF (val_obj);
 780   return pretty_printer;
 781 }
 782
 783 /* A Python function which wraps find_pretty_printer and instantiates
 784    the resulting class.  This accepts a Value argument and returns a
 785    pretty printer instance, or None.  This function is useful as an
 786    argument to the MI command -var-set-visualizer.  */
 787 PyObject *
 788 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 789 {
 790   PyObject *val_obj;
 791   PyObject *cons;
 792   struct value *value;
 793
 794   if (! PyArg_ParseTuple (args, "O", &val_obj))
 795     return NULL;
 796   value = value_object_to_value (val_obj);
 797   if (! value)
 798     {
 799       PyErr_SetString (PyExc_TypeError,
 800                        _("Argument must be a gdb.Value."));
 801       return NULL;
 802     }
 803
 804   cons = find_pretty_printer (val_obj);
 805   return cons;
 806 }
 807
 808 #else /* HAVE_PYTHON */
 809
 810 int
 811 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 812                           int embedded_offset, CORE_ADDR address,
 813                           struct ui_file *stream, int recurse,
 814                           const struct value *val,
 815                           const struct value_print_options *options,
 816                           const struct language_defn *language)
 817 {
 818   return 0;
 819 }
 820
 821 #endif /* HAVE_PYTHON */