gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2013 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 (gdb_python_module == NULL
 166       || ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
 167     Py_RETURN_NONE;
 168   pp_list = PyObject_GetAttrString (gdb_python_module, "pretty_printers");
 169   if (pp_list == NULL || ! PyList_Check (pp_list))
 170     {
 171       Py_XDECREF (pp_list);
 172       Py_RETURN_NONE;
 173     }
 174
 175   function = search_pp_list (pp_list, value);
 176   Py_XDECREF (pp_list);
 177   return function;
 178 }
 179
 180 /* Find the pretty-printing constructor function for VALUE.  If no
 181    pretty-printer exists, return None.  If one exists, return a new
 182    reference.  On error, set the Python error and return NULL.  */
 183
 184 static PyObject *
 185 find_pretty_printer (PyObject *value)
 186 {
 187   PyObject *function;
 188
 189   /* Look at the pretty-printer list for each objfile
 190      in the current program-space.  */
 191   function = find_pretty_printer_from_objfiles (value);
 192   if (function == NULL || function != Py_None)
 193     return function;
 194   Py_DECREF (function);
 195
 196   /* Look at the pretty-printer list for the current program-space.  */
 197   function = find_pretty_printer_from_progspace (value);
 198   if (function == NULL || function != Py_None)
 199     return function;
 200   Py_DECREF (function);
 201
 202   /* Look at the pretty-printer list in the gdb module.  */
 203   function = find_pretty_printer_from_gdb (value);
 204   return function;
 205 }
 206
 207 /* Pretty-print a single value, via the printer object PRINTER.
 208    If the function returns a string, a PyObject containing the string
 209    is returned.  If the function returns Py_NONE that means the pretty
 210    printer returned the Python None as a value.  Otherwise, if the
 211    function returns a value,  *OUT_VALUE is set to the value, and NULL
 212    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 213    returned, with a python exception set.  */
 214
 215 static PyObject *
 216 pretty_print_one_value (PyObject *printer, struct value **out_value)
 217 {
 218   volatile struct gdb_exception except;
 219   PyObject *result = NULL;
 220
 221   *out_value = NULL;
 222   TRY_CATCH (except, RETURN_MASK_ALL)
 223     {
 224       result = PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst, NULL);
 225       if (result)
 226         {
 227           if (! gdbpy_is_string (result) && ! gdbpy_is_lazy_string (result)
 228               && result != Py_None)
 229             {
 230               *out_value = convert_value_from_python (result);
 231               if (PyErr_Occurred ())
 232                 *out_value = NULL;
 233               Py_DECREF (result);
 234               result = NULL;
 235             }
 236         }
 237     }
 238
 239   return result;
 240 }
 241
 242 /* Return the display hint for the object printer, PRINTER.  Return
 243    NULL if there is no display_hint method, or if the method did not
 244    return a string.  On error, print stack trace and return NULL.  On
 245    success, return an xmalloc()d string.  */
 246 char *
 247 gdbpy_get_display_hint (PyObject *printer)
 248 {
 249   PyObject *hint;
 250   char *result = NULL;
 251
 252   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 253     return NULL;
 254
 255   hint = PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst, NULL);
 256   if (hint)
 257     {
 258       if (gdbpy_is_string (hint))
 259         {
 260           result = python_string_to_host_string (hint);
 261           if (result == NULL)
 262             gdbpy_print_stack ();
 263         }
 264       Py_DECREF (hint);
 265     }
 266   else
 267     gdbpy_print_stack ();
 268
 269   return result;
 270 }
 271
 272 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 273
 274 static void
 275 print_stack_unless_memory_error (struct ui_file *stream)
 276 {
 277   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 278     {
 279       struct cleanup *cleanup;
 280       PyObject *type, *value, *trace;
 281       char *msg;
 282
 283       PyErr_Fetch (&type, &value, &trace);
 284       cleanup = make_cleanup_py_decref (type);
 285       make_cleanup_py_decref (value);
 286       make_cleanup_py_decref (trace);
 287
 288       msg = gdbpy_exception_to_string (type, value);
 289       make_cleanup (xfree, msg);
 290
 291       if (msg == NULL || *msg == '\0')
 292         fprintf_filtered (stream, _("<error reading variable>"));
 293       else
 294         fprintf_filtered (stream, _("<error reading variable: %s>"), msg);
 295
 296       do_cleanups (cleanup);
 297     }
 298   else
 299     gdbpy_print_stack ();
 300 }
 301
 302 /* Helper for apply_val_pretty_printer which calls to_string and
 303    formats the result.  */
 304
 305 static enum string_repr_result
 306 print_string_repr (PyObject *printer, const char *hint,
 307                    struct ui_file *stream, int recurse,
 308                    const struct value_print_options *options,
 309                    const struct language_defn *language,
 310                    struct gdbarch *gdbarch)
 311 {
 312   struct value *replacement = NULL;
 313   PyObject *py_str = NULL;
 314   enum string_repr_result result = string_repr_ok;
 315
 316   py_str = pretty_print_one_value (printer, &replacement);
 317   if (py_str)
 318     {
 319       struct cleanup *cleanup = make_cleanup_py_decref (py_str);
 320
 321       if (py_str == Py_None)
 322         result = string_repr_none;
 323       else if (gdbpy_is_lazy_string (py_str))
 324         {
 325           CORE_ADDR addr;
 326           long length;
 327           struct type *type;
 328           char *encoding = NULL;
 329           struct value_print_options local_opts = *options;
 330
 331           make_cleanup (free_current_contents, &encoding);
 332           gdbpy_extract_lazy_string (py_str, &addr, &type,
 333                                      &length, &encoding);
 334
 335           local_opts.addressprint = 0;
 336           val_print_string (type, encoding, addr, (int) length,
 337                             stream, &local_opts);
 338         }
 339       else
 340         {
 341           PyObject *string;
 342
 343           string = python_string_to_target_python_string (py_str);
 344           if (string)
 345             {
 346               char *output;
 347               long length;
 348               struct type *type;
 349
 350               make_cleanup_py_decref (string);
 351 #ifdef IS_PY3K
 352               output = PyBytes_AS_STRING (string);
 353               length = PyBytes_GET_SIZE (string);
 354 #else
 355               output = PyString_AsString (string);
 356               length = PyString_Size (string);
 357 #endif
 358               type = builtin_type (gdbarch)->builtin_char;
 359
 360               if (hint && !strcmp (hint, "string"))
 361                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 362                                  length, NULL, 0, options);
 363               else
 364                 fputs_filtered (output, stream);
 365             }
 366           else
 367             {
 368               result = string_repr_error;
 369               print_stack_unless_memory_error (stream);
 370             }
 371         }
 372
 373       do_cleanups (cleanup);
 374     }
 375   else if (replacement)
 376     {
 377       struct value_print_options opts = *options;
 378
 379       opts.addressprint = 0;
 380       common_val_print (replacement, stream, recurse, &opts, language);
 381     }
 382   else
 383     {
 384       result = string_repr_error;
 385       print_stack_unless_memory_error (stream);
 386     }
 387
 388   return result;
 389 }
 390
 391 #ifndef IS_PY3K
 392 static void
 393 py_restore_tstate (void *p)
 394 {
 395   PyFrameObject *frame = p;
 396   PyThreadState *tstate = PyThreadState_GET ();
 397
 398   tstate->frame = frame;
 399 }
 400
 401 /* Create a dummy PyFrameObject, needed to work around
 402    a Python-2.4 bug with generators.  */
 403 static PyObject *
 404 push_dummy_python_frame (void)
 405 {
 406   PyObject *empty_string, *null_tuple, *globals;
 407   PyCodeObject *code;
 408   PyFrameObject *frame;
 409   PyThreadState *tstate;
 410
 411   empty_string = PyString_FromString ("");
 412   if (!empty_string)
 413     return NULL;
 414
 415   null_tuple = PyTuple_New (0);
 416   if (!null_tuple)
 417     {
 418       Py_DECREF (empty_string);
 419       return NULL;
 420     }
 421
 422   code = PyCode_New (0,                 /* argcount */
 423                      0,                 /* nlocals */
 424                      0,                 /* stacksize */
 425                      0,                 /* flags */
 426                      empty_string,      /* code */
 427                      null_tuple,        /* consts */
 428                      null_tuple,        /* names */
 429                      null_tuple,        /* varnames */
 430 #if PYTHON_API_VERSION >= 1010
 431                      null_tuple,        /* freevars */
 432                      null_tuple,        /* cellvars */
 433 #endif
 434                      empty_string,      /* filename */
 435                      empty_string,      /* name */
 436                      1,                 /* firstlineno */
 437                      empty_string       /* lnotab */
 438                     );
 439
 440   Py_DECREF (empty_string);
 441   Py_DECREF (null_tuple);
 442
 443   if (!code)
 444     return NULL;
 445
 446   globals = PyDict_New ();
 447   if (!globals)
 448     {
 449       Py_DECREF (code);
 450       return NULL;
 451     }
 452
 453   tstate = PyThreadState_GET ();
 454
 455   frame = PyFrame_New (tstate, code, globals, NULL);
 456
 457   Py_DECREF (globals);
 458   Py_DECREF (code);
 459
 460   if (!frame)
 461     return NULL;
 462
 463   tstate->frame = frame;
 464   make_cleanup (py_restore_tstate, frame->f_back);
 465   return (PyObject *) frame;
 466 }
 467 #endif
 468
 469 /* Helper for apply_val_pretty_printer that formats children of the
 470    printer, if any exist.  If is_py_none is true, then nothing has
 471    been printed by to_string, and format output accordingly. */
 472 static void
 473 print_children (PyObject *printer, const char *hint,
 474                 struct ui_file *stream, int recurse,
 475                 const struct value_print_options *options,
 476                 const struct language_defn *language,
 477                 int is_py_none)
 478 {
 479   int is_map, is_array, done_flag, pretty;
 480   unsigned int i;
 481   PyObject *children, *iter;
 482 #ifndef IS_PY3K
 483   PyObject *frame;
 484 #endif
 485   struct cleanup *cleanups;
 486
 487   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 488     return;
 489
 490   /* If we are printing a map or an array, we want some special
 491      formatting.  */
 492   is_map = hint && ! strcmp (hint, "map");
 493   is_array = hint && ! strcmp (hint, "array");
 494
 495   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 496                                          NULL);
 497   if (! children)
 498     {
 499       print_stack_unless_memory_error (stream);
 500       return;
 501     }
 502
 503   cleanups = make_cleanup_py_decref (children);
 504
 505   iter = PyObject_GetIter (children);
 506   if (!iter)
 507     {
 508       print_stack_unless_memory_error (stream);
 509       goto done;
 510     }
 511   make_cleanup_py_decref (iter);
 512
 513   /* Use the prettyprint_arrays option if we are printing an array,
 514      and the pretty option otherwise.  */
 515   if (is_array)
 516     pretty = options->prettyprint_arrays;
 517   else
 518     {
 519       if (options->pretty == Val_prettyprint)
 520         pretty = 1;
 521       else
 522         pretty = options->prettyprint_structs;
 523     }
 524
 525   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 526      where it insists on having a non-NULL tstate->frame when
 527      a generator is called.  */
 528 #ifndef IS_PY3K
 529   frame = push_dummy_python_frame ();
 530   if (!frame)
 531     {
 532       gdbpy_print_stack ();
 533       goto done;
 534     }
 535   make_cleanup_py_decref (frame);
 536 #endif
 537
 538   done_flag = 0;
 539   for (i = 0; i < options->print_max; ++i)
 540     {
 541       PyObject *py_v, *item = PyIter_Next (iter);
 542       const char *name;
 543       struct cleanup *inner_cleanup;
 544
 545       if (! item)
 546         {
 547           if (PyErr_Occurred ())
 548             print_stack_unless_memory_error (stream);
 549           /* Set a flag so we can know whether we printed all the
 550              available elements.  */
 551           else
 552             done_flag = 1;
 553           break;
 554         }
 555
 556       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 557         {
 558           gdbpy_print_stack ();
 559           Py_DECREF (item);
 560           continue;
 561         }
 562       inner_cleanup = make_cleanup_py_decref (item);
 563
 564       /* Print initial "{".  For other elements, there are three
 565          cases:
 566          1. Maps.  Print a "," after each value element.
 567          2. Arrays.  Always print a ",".
 568          3. Other.  Always print a ",".  */
 569       if (i == 0)
 570         {
 571          if (is_py_none)
 572            fputs_filtered ("{", stream);
 573          else
 574            fputs_filtered (" = {", stream);
 575        }
 576
 577       else if (! is_map || i % 2 == 0)
 578         fputs_filtered (pretty ? "," : ", ", stream);
 579
 580       /* In summary mode, we just want to print "= {...}" if there is
 581          a value.  */
 582       if (options->summary)
 583         {
 584           /* This increment tricks the post-loop logic to print what
 585              we want.  */
 586           ++i;
 587           /* Likewise.  */
 588           pretty = 0;
 589           break;
 590         }
 591
 592       if (! is_map || i % 2 == 0)
 593         {
 594           if (pretty)
 595             {
 596               fputs_filtered ("\n", stream);
 597               print_spaces_filtered (2 + 2 * recurse, stream);
 598             }
 599           else
 600             wrap_here (n_spaces (2 + 2 *recurse));
 601         }
 602
 603       if (is_map && i % 2 == 0)
 604         fputs_filtered ("[", stream);
 605       else if (is_array)
 606         {
 607           /* We print the index, not whatever the child method
 608              returned as the name.  */
 609           if (options->print_array_indexes)
 610             fprintf_filtered (stream, "[%d] = ", i);
 611         }
 612       else if (! is_map)
 613         {
 614           fputs_filtered (name, stream);
 615           fputs_filtered (" = ", stream);
 616         }
 617
 618       if (gdbpy_is_lazy_string (py_v))
 619         {
 620           CORE_ADDR addr;
 621           struct type *type;
 622           long length;
 623           char *encoding = NULL;
 624           struct value_print_options local_opts = *options;
 625
 626           make_cleanup (free_current_contents, &encoding);
 627           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 628
 629           local_opts.addressprint = 0;
 630           val_print_string (type, encoding, addr, (int) length, stream,
 631                             &local_opts);
 632
 633           do_cleanups (inner_cleanup);
 634         }
 635       else if (gdbpy_is_string (py_v))
 636         {
 637           char *output;
 638
 639           output = python_string_to_host_string (py_v);
 640           if (!output)
 641             gdbpy_print_stack ();
 642           else
 643             {
 644               fputs_filtered (output, stream);
 645               xfree (output);
 646             }
 647         }
 648       else
 649         {
 650           struct value *value = convert_value_from_python (py_v);
 651
 652           if (value == NULL)
 653             {
 654               gdbpy_print_stack ();
 655               error (_("Error while executing Python code."));
 656             }
 657           else
 658             common_val_print (value, stream, recurse + 1, options, language);
 659         }
 660
 661       if (is_map && i % 2 == 0)
 662         fputs_filtered ("] = ", stream);
 663
 664       do_cleanups (inner_cleanup);
 665     }
 666
 667   if (i)
 668     {
 669       if (!done_flag)
 670         {
 671           if (pretty)
 672             {
 673               fputs_filtered ("\n", stream);
 674               print_spaces_filtered (2 + 2 * recurse, stream);
 675             }
 676           fputs_filtered ("...", stream);
 677         }
 678       if (pretty)
 679         {
 680           fputs_filtered ("\n", stream);
 681           print_spaces_filtered (2 * recurse, stream);
 682         }
 683       fputs_filtered ("}", stream);
 684     }
 685
 686  done:
 687   do_cleanups (cleanups);
 688 }
 689
 690 int
 691 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 692                           int embedded_offset, CORE_ADDR address,
 693                           struct ui_file *stream, int recurse,
 694                           const struct value *val,
 695                           const struct value_print_options *options,
 696                           const struct language_defn *language)
 697 {
 698   struct gdbarch *gdbarch = get_type_arch (type);
 699   PyObject *printer = NULL;
 700   PyObject *val_obj = NULL;
 701   struct value *value;
 702   char *hint = NULL;
 703   struct cleanup *cleanups;
 704   int result = 0;
 705   enum string_repr_result print_result;
 706
 707   /* No pretty-printer support for unavailable values.  */
 708   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 709     return 0;
 710
 711   if (!gdb_python_initialized)
 712     return 0;
 713
 714   cleanups = ensure_python_env (gdbarch, language);
 715
 716   /* Instantiate the printer.  */
 717   if (valaddr)
 718     valaddr += embedded_offset;
 719   value = value_from_contents_and_address (type, valaddr,
 720                                            address + embedded_offset);
 721
 722   set_value_component_location (value, val);
 723   /* set_value_component_location resets the address, so we may
 724      need to set it again.  */
 725   if (VALUE_LVAL (value) != lval_internalvar
 726       && VALUE_LVAL (value) != lval_internalvar_component
 727       && VALUE_LVAL (value) != lval_computed)
 728     set_value_address (value, address + embedded_offset);
 729
 730   val_obj = value_to_value_object (value);
 731   if (! val_obj)
 732     goto done;
 733
 734   /* Find the constructor.  */
 735   printer = find_pretty_printer (val_obj);
 736   Py_DECREF (val_obj);
 737   make_cleanup_py_decref (printer);
 738   if (! printer || printer == Py_None)
 739     goto done;
 740
 741   /* If we are printing a map, we want some special formatting.  */
 742   hint = gdbpy_get_display_hint (printer);
 743   make_cleanup (free_current_contents, &hint);
 744
 745   /* Print the section */
 746   print_result = print_string_repr (printer, hint, stream, recurse,
 747                                     options, language, gdbarch);
 748   if (print_result != string_repr_error)
 749     print_children (printer, hint, stream, recurse, options, language,
 750                     print_result == string_repr_none);
 751
 752   result = 1;
 753
 754
 755  done:
 756   if (PyErr_Occurred ())
 757     print_stack_unless_memory_error (stream);
 758   do_cleanups (cleanups);
 759   return result;
 760 }
 761
 762
 763 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 764    print object.  It must have a 'to_string' method (but this is
 765    checked by varobj, not here) which takes no arguments and
 766    returns a string.  The printer will return a value and in the case
 767    of a Python string being returned, this function will return a
 768    PyObject containing the string.  For any other type, *REPLACEMENT is
 769    set to the replacement value and this function returns NULL.  On
 770    error, *REPLACEMENT is set to NULL and this function also returns
 771    NULL.  */
 772 PyObject *
 773 apply_varobj_pretty_printer (PyObject *printer_obj,
 774                              struct value **replacement,
 775                              struct ui_file *stream)
 776 {
 777   PyObject *py_str = NULL;
 778
 779   *replacement = NULL;
 780   py_str = pretty_print_one_value (printer_obj, replacement);
 781
 782   if (*replacement == NULL && py_str == NULL)
 783     print_stack_unless_memory_error (stream);
 784
 785   return py_str;
 786 }
 787
 788 /* Find a pretty-printer object for the varobj module.  Returns a new
 789    reference to the object if successful; returns NULL if not.  VALUE
 790    is the value for which a printer tests to determine if it
 791    can pretty-print the value.  */
 792 PyObject *
 793 gdbpy_get_varobj_pretty_printer (struct value *value)
 794 {
 795   PyObject *val_obj;
 796   PyObject *pretty_printer = NULL;
 797   volatile struct gdb_exception except;
 798
 799   TRY_CATCH (except, RETURN_MASK_ALL)
 800     {
 801       value = value_copy (value);
 802     }
 803   GDB_PY_HANDLE_EXCEPTION (except);
 804
 805   val_obj = value_to_value_object (value);
 806   if (! val_obj)
 807     return NULL;
 808
 809   pretty_printer = find_pretty_printer (val_obj);
 810   Py_DECREF (val_obj);
 811   return pretty_printer;
 812 }
 813
 814 /* A Python function which wraps find_pretty_printer and instantiates
 815    the resulting class.  This accepts a Value argument and returns a
 816    pretty printer instance, or None.  This function is useful as an
 817    argument to the MI command -var-set-visualizer.  */
 818 PyObject *
 819 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 820 {
 821   PyObject *val_obj;
 822   PyObject *cons;
 823   struct value *value;
 824
 825   if (! PyArg_ParseTuple (args, "O", &val_obj))
 826     return NULL;
 827   value = value_object_to_value (val_obj);
 828   if (! value)
 829     {
 830       PyErr_SetString (PyExc_TypeError,
 831                        _("Argument must be a gdb.Value."));
 832       return NULL;
 833     }
 834
 835   cons = find_pretty_printer (val_obj);
 836   return cons;
 837 }
 838
 839 #else /* HAVE_PYTHON */
 840
 841 int
 842 apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
 843                           int embedded_offset, CORE_ADDR address,
 844                           struct ui_file *stream, int recurse,
 845                           const struct value *val,
 846                           const struct value_print_options *options,
 847                           const struct language_defn *language)
 848 {
 849   return 0;
 850 }
 851
 852 #endif /* HAVE_PYTHON */