gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2017 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 "objfiles.h"
  22 #include "symtab.h"
  23 #include "language.h"
  24 #include "valprint.h"
  25 #include "extension-priv.h"
  26 #include "python.h"
  27 #include "python-internal.h"
  28 #include "py-ref.h"
  29
  30 /* Return type of print_string_repr.  */
  31
  32 enum string_repr_result
  33   {
  34     /* The string method returned None.  */
  35     string_repr_none,
  36     /* The string method had an error.  */
  37     string_repr_error,
  38     /* Everything ok.  */
  39     string_repr_ok
  40   };
  41
  42 /* Helper function for find_pretty_printer which iterates over a list,
  43    calls each function and inspects output.  This will return a
  44    printer object if one recognizes VALUE.  If no printer is found, it
  45    will return None.  On error, it will set the Python error and
  46    return NULL.  */
  47
  48 static PyObject *
  49 search_pp_list (PyObject *list, PyObject *value)
  50 {
  51   Py_ssize_t pp_list_size, list_index;
  52
  53   pp_list_size = PyList_Size (list);
  54   for (list_index = 0; list_index < pp_list_size; list_index++)
  55     {
  56       PyObject *function = PyList_GetItem (list, list_index);
  57       if (! function)
  58         return NULL;
  59
  60       /* Skip if disabled.  */
  61       if (PyObject_HasAttr (function, gdbpy_enabled_cst))
  62         {
  63           gdbpy_ref attr (PyObject_GetAttr (function, gdbpy_enabled_cst));
  64           int cmp;
  65
  66           if (attr == NULL)
  67             return NULL;
  68           cmp = PyObject_IsTrue (attr.get ());
  69           if (cmp == -1)
  70             return NULL;
  71
  72           if (!cmp)
  73             continue;
  74         }
  75
  76       gdbpy_ref printer (PyObject_CallFunctionObjArgs (function, value, NULL));
  77       if (printer == NULL)
  78         return NULL;
  79       else if (printer != Py_None)
  80         return printer.release ();
  81     }
  82
  83   Py_RETURN_NONE;
  84 }
  85
  86 /* Subroutine of find_pretty_printer to simplify it.
  87    Look for a pretty-printer to print VALUE in all objfiles.
  88    The result is NULL if there's an error and the search should be terminated.
  89    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
  90    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
  91
  92 static PyObject *
  93 find_pretty_printer_from_objfiles (PyObject *value)
  94 {
  95   struct objfile *obj;
  96
  97   ALL_OBJFILES (obj)
  98   {
  99     PyObject *objf = objfile_to_objfile_object (obj);
 100     if (!objf)
 101       {
 102         /* Ignore the error and continue.  */
 103         PyErr_Clear ();
 104         continue;
 105       }
 106
 107     gdbpy_ref pp_list (objfpy_get_printers (objf, NULL));
 108     gdbpy_ref function (search_pp_list (pp_list.get (), value));
 109
 110     /* If there is an error in any objfile list, abort the search and exit.  */
 111     if (function == NULL)
 112       return NULL;
 113
 114     if (function != Py_None)
 115       return function.release ();
 116   }
 117
 118   Py_RETURN_NONE;
 119 }
 120
 121 /* Subroutine of find_pretty_printer to simplify it.
 122    Look for a pretty-printer to print VALUE in the current program space.
 123    The result is NULL if there's an error and the search should be terminated.
 124    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 125    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 126
 127 static PyObject *
 128 find_pretty_printer_from_progspace (PyObject *value)
 129 {
 130   PyObject *obj = pspace_to_pspace_object (current_program_space);
 131
 132   if (!obj)
 133     return NULL;
 134   gdbpy_ref pp_list (pspy_get_printers (obj, NULL));
 135   return search_pp_list (pp_list.get (), value);
 136 }
 137
 138 /* Subroutine of find_pretty_printer to simplify it.
 139    Look for a pretty-printer to print VALUE in the gdb module.
 140    The result is NULL if there's an error and the search should be terminated.
 141    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 142    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 143
 144 static PyObject *
 145 find_pretty_printer_from_gdb (PyObject *value)
 146 {
 147   /* Fetch the global pretty printer list.  */
 148   if (gdb_python_module == NULL
 149       || ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
 150     Py_RETURN_NONE;
 151   gdbpy_ref pp_list (PyObject_GetAttrString (gdb_python_module,
 152                                              "pretty_printers"));
 153   if (pp_list == NULL || ! PyList_Check (pp_list.get ()))
 154     Py_RETURN_NONE;
 155
 156   return search_pp_list (pp_list.get (), value);
 157 }
 158
 159 /* Find the pretty-printing constructor function for VALUE.  If no
 160    pretty-printer exists, return None.  If one exists, return a new
 161    reference.  On error, set the Python error and return NULL.  */
 162
 163 static PyObject *
 164 find_pretty_printer (PyObject *value)
 165 {
 166   /* Look at the pretty-printer list for each objfile
 167      in the current program-space.  */
 168   gdbpy_ref function (find_pretty_printer_from_objfiles (value));
 169   if (function == NULL || function != Py_None)
 170     return function.release ();
 171
 172   /* Look at the pretty-printer list for the current program-space.  */
 173   function.reset (find_pretty_printer_from_progspace (value));
 174   if (function == NULL || function != Py_None)
 175     return function.release ();
 176
 177   /* Look at the pretty-printer list in the gdb module.  */
 178   return find_pretty_printer_from_gdb (value);
 179 }
 180
 181 /* Pretty-print a single value, via the printer object PRINTER.
 182    If the function returns a string, a PyObject containing the string
 183    is returned.  If the function returns Py_NONE that means the pretty
 184    printer returned the Python None as a value.  Otherwise, if the
 185    function returns a value,  *OUT_VALUE is set to the value, and NULL
 186    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 187    returned, with a python exception set.  */
 188
 189 static PyObject *
 190 pretty_print_one_value (PyObject *printer, struct value **out_value)
 191 {
 192   PyObject *result = NULL;
 193
 194   *out_value = NULL;
 195   TRY
 196     {
 197       result = PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst, NULL);
 198       if (result)
 199         {
 200           if (! gdbpy_is_string (result) && ! gdbpy_is_lazy_string (result)
 201               && result != Py_None)
 202             {
 203               *out_value = convert_value_from_python (result);
 204               if (PyErr_Occurred ())
 205                 *out_value = NULL;
 206               Py_DECREF (result);
 207               result = NULL;
 208             }
 209         }
 210     }
 211   CATCH (except, RETURN_MASK_ALL)
 212     {
 213     }
 214   END_CATCH
 215
 216   return result;
 217 }
 218
 219 /* Return the display hint for the object printer, PRINTER.  Return
 220    NULL if there is no display_hint method, or if the method did not
 221    return a string.  On error, print stack trace and return NULL.  On
 222    success, return an xmalloc()d string.  */
 223 gdb::unique_xmalloc_ptr<char>
 224 gdbpy_get_display_hint (PyObject *printer)
 225 {
 226   gdb::unique_xmalloc_ptr<char> result;
 227
 228   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 229     return NULL;
 230
 231   gdbpy_ref hint (PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst,
 232                                               NULL));
 233   if (hint != NULL)
 234     {
 235       if (gdbpy_is_string (hint.get ()))
 236         {
 237           result = python_string_to_host_string (hint.get ());
 238           if (result == NULL)
 239             gdbpy_print_stack ();
 240         }
 241     }
 242   else
 243     gdbpy_print_stack ();
 244
 245   return result;
 246 }
 247
 248 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 249
 250 static void
 251 print_stack_unless_memory_error (struct ui_file *stream)
 252 {
 253   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 254     {
 255       struct cleanup *cleanup;
 256       PyObject *type, *value, *trace;
 257
 258       PyErr_Fetch (&type, &value, &trace);
 259       cleanup = make_cleanup_py_decref (type);
 260       make_cleanup_py_decref (value);
 261       make_cleanup_py_decref (trace);
 262
 263       gdb::unique_xmalloc_ptr<char>
 264         msg (gdbpy_exception_to_string (type, value));
 265
 266       if (msg == NULL || *msg == '\0')
 267         fprintf_filtered (stream, _("<error reading variable>"));
 268       else
 269         fprintf_filtered (stream, _("<error reading variable: %s>"),
 270                           msg.get ());
 271
 272       do_cleanups (cleanup);
 273     }
 274   else
 275     gdbpy_print_stack ();
 276 }
 277
 278 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 279    formats the result.  */
 280
 281 static enum string_repr_result
 282 print_string_repr (PyObject *printer, const char *hint,
 283                    struct ui_file *stream, int recurse,
 284                    const struct value_print_options *options,
 285                    const struct language_defn *language,
 286                    struct gdbarch *gdbarch)
 287 {
 288   struct value *replacement = NULL;
 289   PyObject *py_str = NULL;
 290   enum string_repr_result result = string_repr_ok;
 291
 292   py_str = pretty_print_one_value (printer, &replacement);
 293   if (py_str)
 294     {
 295       struct cleanup *cleanup = make_cleanup_py_decref (py_str);
 296
 297       if (py_str == Py_None)
 298         result = string_repr_none;
 299       else if (gdbpy_is_lazy_string (py_str))
 300         {
 301           CORE_ADDR addr;
 302           long length;
 303           struct type *type;
 304           gdb::unique_xmalloc_ptr<char> encoding;
 305           struct value_print_options local_opts = *options;
 306
 307           gdbpy_extract_lazy_string (py_str, &addr, &type,
 308                                      &length, &encoding);
 309
 310           local_opts.addressprint = 0;
 311           val_print_string (type, encoding.get (), addr, (int) length,
 312                             stream, &local_opts);
 313         }
 314       else
 315         {
 316           PyObject *string;
 317
 318           string = python_string_to_target_python_string (py_str);
 319           if (string)
 320             {
 321               char *output;
 322               long length;
 323               struct type *type;
 324
 325               make_cleanup_py_decref (string);
 326 #ifdef IS_PY3K
 327               output = PyBytes_AS_STRING (string);
 328               length = PyBytes_GET_SIZE (string);
 329 #else
 330               output = PyString_AsString (string);
 331               length = PyString_Size (string);
 332 #endif
 333               type = builtin_type (gdbarch)->builtin_char;
 334
 335               if (hint && !strcmp (hint, "string"))
 336                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 337                                  length, NULL, 0, options);
 338               else
 339                 fputs_filtered (output, stream);
 340             }
 341           else
 342             {
 343               result = string_repr_error;
 344               print_stack_unless_memory_error (stream);
 345             }
 346         }
 347
 348       do_cleanups (cleanup);
 349     }
 350   else if (replacement)
 351     {
 352       struct value_print_options opts = *options;
 353
 354       opts.addressprint = 0;
 355       common_val_print (replacement, stream, recurse, &opts, language);
 356     }
 357   else
 358     {
 359       result = string_repr_error;
 360       print_stack_unless_memory_error (stream);
 361     }
 362
 363   return result;
 364 }
 365
 366 #ifndef IS_PY3K
 367 static void
 368 py_restore_tstate (void *p)
 369 {
 370   PyFrameObject *frame = (PyFrameObject *) p;
 371   PyThreadState *tstate = PyThreadState_GET ();
 372
 373   tstate->frame = frame;
 374 }
 375
 376 /* Create a dummy PyFrameObject, needed to work around
 377    a Python-2.4 bug with generators.  */
 378 static PyObject *
 379 push_dummy_python_frame (void)
 380 {
 381   PyObject *empty_string, *null_tuple, *globals;
 382   PyCodeObject *code;
 383   PyFrameObject *frame;
 384   PyThreadState *tstate;
 385
 386   empty_string = PyString_FromString ("");
 387   if (!empty_string)
 388     return NULL;
 389
 390   null_tuple = PyTuple_New (0);
 391   if (!null_tuple)
 392     {
 393       Py_DECREF (empty_string);
 394       return NULL;
 395     }
 396
 397   code = PyCode_New (0,                 /* argcount */
 398                      0,                 /* nlocals */
 399                      0,                 /* stacksize */
 400                      0,                 /* flags */
 401                      empty_string,      /* code */
 402                      null_tuple,        /* consts */
 403                      null_tuple,        /* names */
 404                      null_tuple,        /* varnames */
 405 #if PYTHON_API_VERSION >= 1010
 406                      null_tuple,        /* freevars */
 407                      null_tuple,        /* cellvars */
 408 #endif
 409                      empty_string,      /* filename */
 410                      empty_string,      /* name */
 411                      1,                 /* firstlineno */
 412                      empty_string       /* lnotab */
 413                     );
 414
 415   Py_DECREF (empty_string);
 416   Py_DECREF (null_tuple);
 417
 418   if (!code)
 419     return NULL;
 420
 421   globals = PyDict_New ();
 422   if (!globals)
 423     {
 424       Py_DECREF (code);
 425       return NULL;
 426     }
 427
 428   tstate = PyThreadState_GET ();
 429
 430   frame = PyFrame_New (tstate, code, globals, NULL);
 431
 432   Py_DECREF (globals);
 433   Py_DECREF (code);
 434
 435   if (!frame)
 436     return NULL;
 437
 438   tstate->frame = frame;
 439   make_cleanup (py_restore_tstate, frame->f_back);
 440   return (PyObject *) frame;
 441 }
 442 #endif
 443
 444 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 445    printer, if any exist.  If is_py_none is true, then nothing has
 446    been printed by to_string, and format output accordingly. */
 447 static void
 448 print_children (PyObject *printer, const char *hint,
 449                 struct ui_file *stream, int recurse,
 450                 const struct value_print_options *options,
 451                 const struct language_defn *language,
 452                 int is_py_none)
 453 {
 454   int is_map, is_array, done_flag, pretty;
 455   unsigned int i;
 456   PyObject *children, *iter;
 457 #ifndef IS_PY3K
 458   PyObject *frame;
 459 #endif
 460   struct cleanup *cleanups;
 461
 462   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 463     return;
 464
 465   /* If we are printing a map or an array, we want some special
 466      formatting.  */
 467   is_map = hint && ! strcmp (hint, "map");
 468   is_array = hint && ! strcmp (hint, "array");
 469
 470   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 471                                          NULL);
 472   if (! children)
 473     {
 474       print_stack_unless_memory_error (stream);
 475       return;
 476     }
 477
 478   cleanups = make_cleanup_py_decref (children);
 479
 480   iter = PyObject_GetIter (children);
 481   if (!iter)
 482     {
 483       print_stack_unless_memory_error (stream);
 484       goto done;
 485     }
 486   make_cleanup_py_decref (iter);
 487
 488   /* Use the prettyformat_arrays option if we are printing an array,
 489      and the pretty option otherwise.  */
 490   if (is_array)
 491     pretty = options->prettyformat_arrays;
 492   else
 493     {
 494       if (options->prettyformat == Val_prettyformat)
 495         pretty = 1;
 496       else
 497         pretty = options->prettyformat_structs;
 498     }
 499
 500   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 501      where it insists on having a non-NULL tstate->frame when
 502      a generator is called.  */
 503 #ifndef IS_PY3K
 504   frame = push_dummy_python_frame ();
 505   if (!frame)
 506     {
 507       gdbpy_print_stack ();
 508       goto done;
 509     }
 510   make_cleanup_py_decref (frame);
 511 #endif
 512
 513   done_flag = 0;
 514   for (i = 0; i < options->print_max; ++i)
 515     {
 516       PyObject *py_v, *item = PyIter_Next (iter);
 517       const char *name;
 518       struct cleanup *inner_cleanup;
 519
 520       if (! item)
 521         {
 522           if (PyErr_Occurred ())
 523             print_stack_unless_memory_error (stream);
 524           /* Set a flag so we can know whether we printed all the
 525              available elements.  */
 526           else
 527             done_flag = 1;
 528           break;
 529         }
 530
 531       if (! PyTuple_Check (item) || PyTuple_Size (item) != 2)
 532         {
 533           PyErr_SetString (PyExc_TypeError,
 534                            _("Result of children iterator not a tuple"
 535                              " of two elements."));
 536           gdbpy_print_stack ();
 537           Py_DECREF (item);
 538           continue;
 539         }
 540       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 541         {
 542           /* The user won't necessarily get a stack trace here, so provide
 543              more context.  */
 544           if (gdbpy_print_python_errors_p ())
 545             fprintf_unfiltered (gdb_stderr,
 546                                 _("Bad result from children iterator.\n"));
 547           gdbpy_print_stack ();
 548           Py_DECREF (item);
 549           continue;
 550         }
 551       inner_cleanup = make_cleanup_py_decref (item);
 552
 553       /* Print initial "{".  For other elements, there are three
 554          cases:
 555          1. Maps.  Print a "," after each value element.
 556          2. Arrays.  Always print a ",".
 557          3. Other.  Always print a ",".  */
 558       if (i == 0)
 559         {
 560          if (is_py_none)
 561            fputs_filtered ("{", stream);
 562          else
 563            fputs_filtered (" = {", stream);
 564        }
 565
 566       else if (! is_map || i % 2 == 0)
 567         fputs_filtered (pretty ? "," : ", ", stream);
 568
 569       /* In summary mode, we just want to print "= {...}" if there is
 570          a value.  */
 571       if (options->summary)
 572         {
 573           /* This increment tricks the post-loop logic to print what
 574              we want.  */
 575           ++i;
 576           /* Likewise.  */
 577           pretty = 0;
 578           break;
 579         }
 580
 581       if (! is_map || i % 2 == 0)
 582         {
 583           if (pretty)
 584             {
 585               fputs_filtered ("\n", stream);
 586               print_spaces_filtered (2 + 2 * recurse, stream);
 587             }
 588           else
 589             wrap_here (n_spaces (2 + 2 *recurse));
 590         }
 591
 592       if (is_map && i % 2 == 0)
 593         fputs_filtered ("[", stream);
 594       else if (is_array)
 595         {
 596           /* We print the index, not whatever the child method
 597              returned as the name.  */
 598           if (options->print_array_indexes)
 599             fprintf_filtered (stream, "[%d] = ", i);
 600         }
 601       else if (! is_map)
 602         {
 603           fputs_filtered (name, stream);
 604           fputs_filtered (" = ", stream);
 605         }
 606
 607       if (gdbpy_is_lazy_string (py_v))
 608         {
 609           CORE_ADDR addr;
 610           struct type *type;
 611           long length;
 612           gdb::unique_xmalloc_ptr<char> encoding;
 613           struct value_print_options local_opts = *options;
 614
 615           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 616
 617           local_opts.addressprint = 0;
 618           val_print_string (type, encoding.get (), addr, (int) length, stream,
 619                             &local_opts);
 620         }
 621       else if (gdbpy_is_string (py_v))
 622         {
 623           gdb::unique_xmalloc_ptr<char> output;
 624
 625           output = python_string_to_host_string (py_v);
 626           if (!output)
 627             gdbpy_print_stack ();
 628           else
 629             fputs_filtered (output.get (), stream);
 630         }
 631       else
 632         {
 633           struct value *value = convert_value_from_python (py_v);
 634
 635           if (value == NULL)
 636             {
 637               gdbpy_print_stack ();
 638               error (_("Error while executing Python code."));
 639             }
 640           else
 641             common_val_print (value, stream, recurse + 1, options, language);
 642         }
 643
 644       if (is_map && i % 2 == 0)
 645         fputs_filtered ("] = ", stream);
 646
 647       do_cleanups (inner_cleanup);
 648     }
 649
 650   if (i)
 651     {
 652       if (!done_flag)
 653         {
 654           if (pretty)
 655             {
 656               fputs_filtered ("\n", stream);
 657               print_spaces_filtered (2 + 2 * recurse, stream);
 658             }
 659           fputs_filtered ("...", stream);
 660         }
 661       if (pretty)
 662         {
 663           fputs_filtered ("\n", stream);
 664           print_spaces_filtered (2 * recurse, stream);
 665         }
 666       fputs_filtered ("}", stream);
 667     }
 668
 669  done:
 670   do_cleanups (cleanups);
 671 }
 672
 673 enum ext_lang_rc
 674 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 675                                 struct type *type,
 676                                 LONGEST embedded_offset, CORE_ADDR address,
 677                                 struct ui_file *stream, int recurse,
 678                                 struct value *val,
 679                                 const struct value_print_options *options,
 680                                 const struct language_defn *language)
 681 {
 682   struct gdbarch *gdbarch = get_type_arch (type);
 683   struct value *value;
 684   enum string_repr_result print_result;
 685   const gdb_byte *valaddr = value_contents_for_printing (val);
 686
 687   /* No pretty-printer support for unavailable values.  */
 688   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 689     return EXT_LANG_RC_NOP;
 690
 691   if (!gdb_python_initialized)
 692     return EXT_LANG_RC_NOP;
 693
 694   gdbpy_enter enter_py (gdbarch, language);
 695
 696   /* Instantiate the printer.  */
 697   value = value_from_component (val, type, embedded_offset);
 698
 699   gdbpy_ref val_obj (value_to_value_object (value));
 700   if (val_obj == NULL)
 701     {
 702       print_stack_unless_memory_error (stream);
 703       return EXT_LANG_RC_ERROR;
 704     }
 705
 706   /* Find the constructor.  */
 707   gdbpy_ref printer (find_pretty_printer (val_obj.get ()));
 708   if (printer == NULL)
 709     {
 710       print_stack_unless_memory_error (stream);
 711       return EXT_LANG_RC_ERROR;
 712     }
 713
 714   if (printer == Py_None)
 715     return EXT_LANG_RC_NOP;
 716
 717   /* If we are printing a map, we want some special formatting.  */
 718   gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
 719
 720   /* Print the section */
 721   print_result = print_string_repr (printer.get (), hint.get (), stream,
 722                                     recurse, options, language, gdbarch);
 723   if (print_result != string_repr_error)
 724     print_children (printer.get (), hint.get (), stream, recurse, options,
 725                     language, print_result == string_repr_none);
 726
 727   if (PyErr_Occurred ())
 728     print_stack_unless_memory_error (stream);
 729   return EXT_LANG_RC_OK;
 730 }
 731
 732
 733 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 734    print object.  It must have a 'to_string' method (but this is
 735    checked by varobj, not here) which takes no arguments and
 736    returns a string.  The printer will return a value and in the case
 737    of a Python string being returned, this function will return a
 738    PyObject containing the string.  For any other type, *REPLACEMENT is
 739    set to the replacement value and this function returns NULL.  On
 740    error, *REPLACEMENT is set to NULL and this function also returns
 741    NULL.  */
 742 PyObject *
 743 apply_varobj_pretty_printer (PyObject *printer_obj,
 744                              struct value **replacement,
 745                              struct ui_file *stream)
 746 {
 747   PyObject *py_str = NULL;
 748
 749   *replacement = NULL;
 750   py_str = pretty_print_one_value (printer_obj, replacement);
 751
 752   if (*replacement == NULL && py_str == NULL)
 753     print_stack_unless_memory_error (stream);
 754
 755   return py_str;
 756 }
 757
 758 /* Find a pretty-printer object for the varobj module.  Returns a new
 759    reference to the object if successful; returns NULL if not.  VALUE
 760    is the value for which a printer tests to determine if it
 761    can pretty-print the value.  */
 762 PyObject *
 763 gdbpy_get_varobj_pretty_printer (struct value *value)
 764 {
 765   TRY
 766     {
 767       value = value_copy (value);
 768     }
 769   CATCH (except, RETURN_MASK_ALL)
 770     {
 771       GDB_PY_HANDLE_EXCEPTION (except);
 772     }
 773   END_CATCH
 774
 775   gdbpy_ref val_obj (value_to_value_object (value));
 776   if (val_obj == NULL)
 777     return NULL;
 778
 779   return find_pretty_printer (val_obj.get ());
 780 }
 781
 782 /* A Python function which wraps find_pretty_printer and instantiates
 783    the resulting class.  This accepts a Value argument and returns a
 784    pretty printer instance, or None.  This function is useful as an
 785    argument to the MI command -var-set-visualizer.  */
 786 PyObject *
 787 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 788 {
 789   PyObject *val_obj;
 790   PyObject *cons;
 791   struct value *value;
 792
 793   if (! PyArg_ParseTuple (args, "O", &val_obj))
 794     return NULL;
 795   value = value_object_to_value (val_obj);
 796   if (! value)
 797     {
 798       PyErr_SetString (PyExc_TypeError,
 799                        _("Argument must be a gdb.Value."));
 800       return NULL;
 801     }
 802
 803   cons = find_pretty_printer (val_obj);
 804   return cons;
 805 }