gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2012 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           struct value_print_options local_opts = *options;
 329
 330           make_cleanup (free_current_contents, &encoding);
 331           gdbpy_extract_lazy_string (py_str, &addr, &type,
 332                                      &length, &encoding);
 333
 334           local_opts.addressprint = 0;
 335           val_print_string (type, encoding, addr, (int) length,
 336                             stream, &local_opts);
 337         }
 338       else
 339         {
 340           PyObject *string;
 341
 342           string = python_string_to_target_python_string (py_str);
 343           if (string)
 344             {
 345               gdb_byte *output;
 346               long length;
 347               struct type *type;
 348
 349               make_cleanup_py_decref (string);
 350               output = PyString_AsString (string);
 351               length = PyString_Size (string);
 352               type = builtin_type (gdbarch)->builtin_char;
 353
 354               if (hint && !strcmp (hint, "string"))
 355                 LA_PRINT_STRING (stream, type, output, length, NULL,
 356                                  0, options);
 357               else
 358                 fputs_filtered (output, stream);
 359             }
 360           else
 361             {
 362               result = string_repr_error;
 363               print_stack_unless_memory_error (stream);
 364             }
 365         }
 366
 367       do_cleanups (cleanup);
 368     }
 369   else if (replacement)
 370     {
 371       struct value_print_options opts = *options;
 372
 373       opts.addressprint = 0;
 374       common_val_print (replacement, stream, recurse, &opts, language);
 375     }
 376   else
 377     {
 378       result = string_repr_error;
 379       print_stack_unless_memory_error (stream);
 380     }
 381
 382   return result;
 383 }
 384
 385 static void
 386 py_restore_tstate (void *p)
 387 {
 388   PyFrameObject *frame = p;
 389   PyThreadState *tstate = PyThreadState_GET ();
 390
 391   tstate->frame = frame;
 392 }
 393
 394 /* Create a dummy PyFrameObject, needed to work around
 395    a Python-2.4 bug with generators.  */
 396 static PyObject *
 397 push_dummy_python_frame (void)
 398 {
 399   PyObject *empty_string, *null_tuple, *globals;
 400   PyCodeObject *code;
 401   PyFrameObject *frame;
 402   PyThreadState *tstate;
 403
 404   empty_string = PyString_FromString ("");
 405   if (!empty_string)
 406     return NULL;
 407
 408   null_tuple = PyTuple_New (0);
 409   if (!null_tuple)
 410     {
 411       Py_DECREF (empty_string);
 412       return NULL;
 413     }
 414
 415   code = PyCode_New (0,                 /* argcount */
 416                      0,                 /* nlocals */
 417                      0,                 /* stacksize */
 418                      0,                 /* flags */
 419                      empty_string,      /* code */
 420                      null_tuple,        /* consts */
 421                      null_tuple,        /* names */
 422                      null_tuple,        /* varnames */
 423 #if PYTHON_API_VERSION >= 1010
 424                      null_tuple,        /* freevars */
 425                      null_tuple,        /* cellvars */
 426 #endif
 427                      empty_string,      /* filename */
 428                      empty_string,      /* name */
 429                      1,                 /* firstlineno */
 430                      empty_string       /* lnotab */
 431                     );
 432
 433   Py_DECREF (empty_string);
 434   Py_DECREF (null_tuple);
 435
 436   if (!code)
 437     return NULL;
 438
 439   globals = PyDict_New ();
 440   if (!globals)
 441     {
 442       Py_DECREF (code);
 443       return NULL;
 444     }
 445
 446   tstate = PyThreadState_GET ();
 447
 448   frame = PyFrame_New (tstate, code, globals, NULL);
 449
 450   Py_DECREF (globals);
 451   Py_DECREF (code);
 452
 453   if (!frame)
 454     return NULL;
 455
 456   tstate->frame = frame;
 457   make_cleanup (py_restore_tstate, frame->f_back);
 458   return (PyObject *) frame;
 459 }
 460
 461 /* Helper for apply_val_pretty_printer that formats children of the
 462    printer, if any exist.  If is_py_none is true, then nothing has
 463    been printed by to_string, and format output accordingly. */
 464 static void
 465 print_children (PyObject *printer, const char *hint,
 466                 struct ui_file *stream, int recurse,
 467                 const struct value_print_options *options,
 468                 const struct language_defn *language,
 469                 int is_py_none)
 470 {
 471   int is_map, is_array, done_flag, pretty;
 472   unsigned int i;
 473   PyObject *children, *iter, *frame;
 474   struct cleanup *cleanups;
 475
 476   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 477     return;
 478
 479   /* If we are printing a map or an array, we want some special
 480      formatting.  */
 481   is_map = hint && ! strcmp (hint, "map");
 482   is_array = hint && ! strcmp (hint, "array");
 483
 484   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 485                                          NULL);
 486   if (! children)
 487     {
 488       print_stack_unless_memory_error (stream);
 489       return;
 490     }
 491
 492   cleanups = make_cleanup_py_decref (children);
 493
 494   iter = PyObject_GetIter (children);
 495   if (!iter)
 496     {
 497       print_stack_unless_memory_error (stream);
 498       goto done;
 499     }
 500   make_cleanup_py_decref (iter);
 501
 502   /* Use the prettyprint_arrays option if we are printing an array,
 503      and the pretty option otherwise.  */
 504   if (is_array)
 505     pretty = options->prettyprint_arrays;
 506   else
 507     {
 508       if (options->pretty == Val_prettyprint)
 509         pretty = 1;
 510       else
 511         pretty = options->prettyprint_structs;
 512     }
 513
 514   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 515      where it insists on having a non-NULL tstate->frame when
 516      a generator is called.  */
 517   frame = push_dummy_python_frame ();
 518   if (!frame)
 519     {
 520       gdbpy_print_stack ();
 521       goto done;
 522     }
 523   make_cleanup_py_decref (frame);
 524
 525   done_flag = 0;
 526   for (i = 0; i < options->print_max; ++i)
 527     {
 528       PyObject *py_v, *item = PyIter_Next (iter);
 529       const char *name;
 530       struct cleanup *inner_cleanup;
 531
 532       if (! item)
 533         {
 534           if (PyErr_Occurred ())
 535             print_stack_unless_memory_error (stream);
 536           /* Set a flag so we can know whether we printed all the
 537              available elements.  */
 538           else
 539             done_flag = 1;
 540           break;
 541         }
 542
 543       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 544         {
 545           gdbpy_print_stack ();
 546           Py_DECREF (item);
 547           continue;
 548         }
 549       inner_cleanup = make_cleanup_py_decref (item);
 550
 551       /* Print initial "{".  For other elements, there are three
 552          cases:
 553          1. Maps.  Print a "," after each value element.
 554          2. Arrays.  Always print a ",".
 555          3. Other.  Always print a ",".  */
 556       if (i == 0)
 557         {
 558          if (is_py_none)
 559            fputs_filtered ("{", stream);
 560          else
 561            fputs_filtered (" = {", stream);
 562        }
 563
 564       else if (! is_map || i % 2 == 0)
 565         fputs_filtered (pretty ? "," : ", ", stream);
 566
 567       /* In summary mode, we just want to print "= {...}" if there is
 568          a value.  */
 569       if (options->summary)
 570         {
 571           /* This increment tricks the post-loop logic to print what
 572              we want.  */
 573           ++i;
 574           /* Likewise.  */
 575           pretty = 0;
 576           break;
 577         }
 578
 579       if (! is_map || i % 2 == 0)
 580         {
 581           if (pretty)
 582             {
 583               fputs_filtered ("\n", stream);
 584               print_spaces_filtered (2 + 2 * recurse, stream);
 585             }
 586           else
 587             wrap_here (n_spaces (2 + 2 *recurse));
 588         }
 589
 590       if (is_map && i % 2 == 0)
 591         fputs_filtered ("[", stream);
 592       else if (is_array)
 593         {
 594           /* We print the index, not whatever the child method
 595              returned as the name.  */
 596           if (options->print_array_indexes)
 597             fprintf_filtered (stream, "[%d] = ", i);
 598         }
 599       else if (! is_map)
 600         {
 601           fputs_filtered (name, stream);
 602           fputs_filtered (" = ", stream);
 603         }
 604
 605       if (gdbpy_is_lazy_string (py_v))
 606         {
 607           CORE_ADDR addr;
 608           struct type *type;
 609           long length;
 610           char *encoding = NULL;
 611           struct value_print_options local_opts = *options;
 612
 613           make_cleanup (free_current_contents, &encoding);
 614           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 615
 616           local_opts.addressprint = 0;
 617           val_print_string (type, encoding, addr, (int) length, stream,
 618                             &local_opts);
 619
 620           do_cleanups (inner_cleanup);
 621         }
 622       else if (gdbpy_is_string (py_v))
 623         {
 624           gdb_byte *output;
 625
 626           output = python_string_to_host_string (py_v);
 627           if (!output)
 628             gdbpy_print_stack ();
 629           else
 630             {
 631               fputs_filtered (output, stream);
 632               xfree (output);
 633             }
 634         }
 635       else
 636         {
 637           struct value *value = convert_value_from_python (py_v);
 638
 639           if (value == NULL)
 640             {
 641               gdbpy_print_stack ();
 642               error (_("Error while executing Python code."));
 643             }
 644           else
 645             common_val_print (value, stream, recurse + 1, options, language);
 646         }
 647
 648       if (is_map && i % 2 == 0)
 649         fputs_filtered ("] = ", stream);
 650
 651       do_cleanups (inner_cleanup);
 652     }
 653
 654   if (i)
 655     {
 656       if (!done_flag)
 657         {
 658           if (pretty)
 659             {
 660               fputs_filtered ("\n", stream);
 661               print_spaces_filtered (2 + 2 * recurse, stream);
 662             }
 663           fputs_filtered ("...", stream);
 664         }
 665       if (pretty)
 666         {
 667           fputs_filtered ("\n", stream);
 668           print_spaces_filtered (2 * recurse, stream);
 669         }
 670       fputs_filtered ("}", stream);
 671     }
 672
 673  done:
 674   do_cleanups (cleanups);
 675 }
 676
 677 int
 678 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 679                           int embedded_offset, CORE_ADDR address,
 680                           struct ui_file *stream, int recurse,
 681                           const struct value *val,
 682                           const struct value_print_options *options,
 683                           const struct language_defn *language)
 684 {
 685   struct gdbarch *gdbarch = get_type_arch (type);
 686   PyObject *printer = NULL;
 687   PyObject *val_obj = NULL;
 688   struct value *value;
 689   char *hint = NULL;
 690   struct cleanup *cleanups;
 691   int result = 0;
 692   enum string_repr_result print_result;
 693
 694   /* No pretty-printer support for unavailable values.  */
 695   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 696     return 0;
 697
 698   cleanups = ensure_python_env (gdbarch, language);
 699
 700   /* Instantiate the printer.  */
 701   if (valaddr)
 702     valaddr += embedded_offset;
 703   value = value_from_contents_and_address (type, valaddr,
 704                                            address + embedded_offset);
 705
 706   set_value_component_location (value, val);
 707   /* set_value_component_location resets the address, so we may
 708      need to set it again.  */
 709   if (VALUE_LVAL (value) != lval_internalvar
 710       && VALUE_LVAL (value) != lval_internalvar_component
 711       && VALUE_LVAL (value) != lval_computed)
 712     set_value_address (value, address + embedded_offset);
 713
 714   val_obj = value_to_value_object (value);
 715   if (! val_obj)
 716     goto done;
 717
 718   /* Find the constructor.  */
 719   printer = find_pretty_printer (val_obj);
 720   Py_DECREF (val_obj);
 721   make_cleanup_py_decref (printer);
 722   if (! printer || printer == Py_None)
 723     goto done;
 724
 725   /* If we are printing a map, we want some special formatting.  */
 726   hint = gdbpy_get_display_hint (printer);
 727   make_cleanup (free_current_contents, &hint);
 728
 729   /* Print the section */
 730   print_result = print_string_repr (printer, hint, stream, recurse,
 731                                     options, language, gdbarch);
 732   if (print_result != string_repr_error)
 733     print_children (printer, hint, stream, recurse, options, language,
 734                     print_result == string_repr_none);
 735
 736   result = 1;
 737
 738
 739  done:
 740   if (PyErr_Occurred ())
 741     print_stack_unless_memory_error (stream);
 742   do_cleanups (cleanups);
 743   return result;
 744 }
 745
 746
 747 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 748    print object.  It must have a 'to_string' method (but this is
 749    checked by varobj, not here) which takes no arguments and
 750    returns a string.  The printer will return a value and in the case
 751    of a Python string being returned, this function will return a
 752    PyObject containing the string.  For any other type, *REPLACEMENT is
 753    set to the replacement value and this function returns NULL.  On
 754    error, *REPLACEMENT is set to NULL and this function also returns
 755    NULL.  */
 756 PyObject *
 757 apply_varobj_pretty_printer (PyObject *printer_obj,
 758                              struct value **replacement,
 759                              struct ui_file *stream)
 760 {
 761   PyObject *py_str = NULL;
 762
 763   *replacement = NULL;
 764   py_str = pretty_print_one_value (printer_obj, replacement);
 765
 766   if (*replacement == NULL && py_str == NULL)
 767     print_stack_unless_memory_error (stream);
 768
 769   return py_str;
 770 }
 771
 772 /* Find a pretty-printer object for the varobj module.  Returns a new
 773    reference to the object if successful; returns NULL if not.  VALUE
 774    is the value for which a printer tests to determine if it
 775    can pretty-print the value.  */
 776 PyObject *
 777 gdbpy_get_varobj_pretty_printer (struct value *value)
 778 {
 779   PyObject *val_obj;
 780   PyObject *pretty_printer = NULL;
 781   volatile struct gdb_exception except;
 782
 783   TRY_CATCH (except, RETURN_MASK_ALL)
 784     {
 785       value = value_copy (value);
 786     }
 787   GDB_PY_HANDLE_EXCEPTION (except);
 788
 789   val_obj = value_to_value_object (value);
 790   if (! val_obj)
 791     return NULL;
 792
 793   pretty_printer = find_pretty_printer (val_obj);
 794   Py_DECREF (val_obj);
 795   return pretty_printer;
 796 }
 797
 798 /* A Python function which wraps find_pretty_printer and instantiates
 799    the resulting class.  This accepts a Value argument and returns a
 800    pretty printer instance, or None.  This function is useful as an
 801    argument to the MI command -var-set-visualizer.  */
 802 PyObject *
 803 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 804 {
 805   PyObject *val_obj;
 806   PyObject *cons;
 807   struct value *value;
 808
 809   if (! PyArg_ParseTuple (args, "O", &val_obj))
 810     return NULL;
 811   value = value_object_to_value (val_obj);
 812   if (! value)
 813     {
 814       PyErr_SetString (PyExc_TypeError,
 815                        _("Argument must be a gdb.Value."));
 816       return NULL;
 817     }
 818
 819   cons = find_pretty_printer (val_obj);
 820   return cons;
 821 }
 822
 823 #else /* HAVE_PYTHON */
 824
 825 int
 826 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 827                           int embedded_offset, CORE_ADDR address,
 828                           struct ui_file *stream, int recurse,
 829                           const struct value *val,
 830                           const struct value_print_options *options,
 831                           const struct language_defn *language)
 832 {
 833   return 0;
 834 }
 835
 836 #endif /* HAVE_PYTHON */