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       PyObject *type, *value, *trace;
 256
 257       PyErr_Fetch (&type, &value, &trace);
 258
 259       gdbpy_ref type_ref (type);
 260       gdbpy_ref value_ref (value);
 261       gdbpy_ref trace_ref (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   else
 273     gdbpy_print_stack ();
 274 }
 275
 276 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 277    formats the result.  */
 278
 279 static enum string_repr_result
 280 print_string_repr (PyObject *printer, const char *hint,
 281                    struct ui_file *stream, int recurse,
 282                    const struct value_print_options *options,
 283                    const struct language_defn *language,
 284                    struct gdbarch *gdbarch)
 285 {
 286   struct value *replacement = NULL;
 287   enum string_repr_result result = string_repr_ok;
 288
 289   gdbpy_ref py_str (pretty_print_one_value (printer, &replacement));
 290   if (py_str != NULL)
 291     {
 292       if (py_str == Py_None)
 293         result = string_repr_none;
 294       else if (gdbpy_is_lazy_string (py_str.get ()))
 295         {
 296           CORE_ADDR addr;
 297           long length;
 298           struct type *type;
 299           gdb::unique_xmalloc_ptr<char> encoding;
 300           struct value_print_options local_opts = *options;
 301
 302           gdbpy_extract_lazy_string (py_str.get (), &addr, &type,
 303                                      &length, &encoding);
 304
 305           local_opts.addressprint = 0;
 306           val_print_string (type, encoding.get (), addr, (int) length,
 307                             stream, &local_opts);
 308         }
 309       else
 310         {
 311           gdbpy_ref string
 312             (python_string_to_target_python_string (py_str.get ()));
 313           if (string != NULL)
 314             {
 315               char *output;
 316               long length;
 317               struct type *type;
 318
 319 #ifdef IS_PY3K
 320               output = PyBytes_AS_STRING (string.get ());
 321               length = PyBytes_GET_SIZE (string.get ());
 322 #else
 323               output = PyString_AsString (string.get ());
 324               length = PyString_Size (string.get ());
 325 #endif
 326               type = builtin_type (gdbarch)->builtin_char;
 327
 328               if (hint && !strcmp (hint, "string"))
 329                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 330                                  length, NULL, 0, options);
 331               else
 332                 fputs_filtered (output, stream);
 333             }
 334           else
 335             {
 336               result = string_repr_error;
 337               print_stack_unless_memory_error (stream);
 338             }
 339         }
 340     }
 341   else if (replacement)
 342     {
 343       struct value_print_options opts = *options;
 344
 345       opts.addressprint = 0;
 346       common_val_print (replacement, stream, recurse, &opts, language);
 347     }
 348   else
 349     {
 350       result = string_repr_error;
 351       print_stack_unless_memory_error (stream);
 352     }
 353
 354   return result;
 355 }
 356
 357 #ifndef IS_PY3K
 358
 359 /* Create a dummy PyFrameObject, needed to work around
 360    a Python-2.4 bug with generators.  */
 361 class dummy_python_frame
 362 {
 363  public:
 364
 365   dummy_python_frame ();
 366
 367   ~dummy_python_frame ()
 368   {
 369     if (m_valid)
 370       m_tstate->frame = m_saved_frame;
 371   }
 372
 373   bool failed () const
 374   {
 375     return !m_valid;
 376   }
 377
 378  private:
 379
 380   bool m_valid;
 381   PyFrameObject *m_saved_frame;
 382   gdbpy_ref m_frame;
 383   PyThreadState *m_tstate;
 384 };
 385
 386 dummy_python_frame::dummy_python_frame ()
 387 : m_valid (false),
 388   m_saved_frame (NULL),
 389   m_tstate (NULL)
 390 {
 391   PyCodeObject *code;
 392   PyFrameObject *frame;
 393
 394   gdbpy_ref empty_string (PyString_FromString (""));
 395   if (empty_string == NULL)
 396     return;
 397
 398   gdbpy_ref null_tuple (PyTuple_New (0));
 399   if (null_tuple == NULL)
 400     return;
 401
 402   code = PyCode_New (0,                   /* argcount */
 403                      0,                   /* locals */
 404                      0,                   /* stacksize */
 405                      0,                   /* flags */
 406                      empty_string.get (), /* code */
 407                      null_tuple.get (),   /* consts */
 408                      null_tuple.get (),   /* names */
 409                      null_tuple.get (),   /* varnames */
 410 #if PYTHON_API_VERSION >= 1010
 411                      null_tuple.get (),   /* freevars */
 412                      null_tuple.get (),   /* cellvars */
 413 #endif
 414                      empty_string.get (), /* filename */
 415                      empty_string.get (), /* name */
 416                      1,                   /* firstlineno */
 417                      empty_string.get ()  /* lnotab */
 418                      );
 419   if (code == NULL)
 420     return;
 421   gdbpy_ref code_holder ((PyObject *) code);
 422
 423   gdbpy_ref globals (PyDict_New ());
 424   if (globals == NULL)
 425     return;
 426
 427   m_tstate = PyThreadState_GET ();
 428   frame = PyFrame_New (m_tstate, code, globals.get (), NULL);
 429   if (frame == NULL)
 430     return;
 431
 432   m_frame.reset ((PyObject *) frame);
 433   m_tstate->frame = frame;
 434   m_saved_frame = frame->f_back;
 435   m_valid = true;
 436 }
 437 #endif
 438
 439 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 440    printer, if any exist.  If is_py_none is true, then nothing has
 441    been printed by to_string, and format output accordingly. */
 442 static void
 443 print_children (PyObject *printer, const char *hint,
 444                 struct ui_file *stream, int recurse,
 445                 const struct value_print_options *options,
 446                 const struct language_defn *language,
 447                 int is_py_none)
 448 {
 449   int is_map, is_array, done_flag, pretty;
 450   unsigned int i;
 451
 452   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 453     return;
 454
 455   /* If we are printing a map or an array, we want some special
 456      formatting.  */
 457   is_map = hint && ! strcmp (hint, "map");
 458   is_array = hint && ! strcmp (hint, "array");
 459
 460   gdbpy_ref children (PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 461                                                   NULL));
 462   if (children == NULL)
 463     {
 464       print_stack_unless_memory_error (stream);
 465       return;
 466     }
 467
 468   gdbpy_ref iter (PyObject_GetIter (children.get ()));
 469   if (iter == NULL)
 470     {
 471       print_stack_unless_memory_error (stream);
 472       return;
 473     }
 474
 475   /* Use the prettyformat_arrays option if we are printing an array,
 476      and the pretty option otherwise.  */
 477   if (is_array)
 478     pretty = options->prettyformat_arrays;
 479   else
 480     {
 481       if (options->prettyformat == Val_prettyformat)
 482         pretty = 1;
 483       else
 484         pretty = options->prettyformat_structs;
 485     }
 486
 487   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 488      where it insists on having a non-NULL tstate->frame when
 489      a generator is called.  */
 490 #ifndef IS_PY3K
 491   dummy_python_frame frame;
 492   if (frame.failed ())
 493     {
 494       gdbpy_print_stack ();
 495       return;
 496     }
 497 #endif
 498
 499   done_flag = 0;
 500   for (i = 0; i < options->print_max; ++i)
 501     {
 502       PyObject *py_v;
 503       const char *name;
 504
 505       gdbpy_ref item (PyIter_Next (iter.get ()));
 506       if (item == NULL)
 507         {
 508           if (PyErr_Occurred ())
 509             print_stack_unless_memory_error (stream);
 510           /* Set a flag so we can know whether we printed all the
 511              available elements.  */
 512           else
 513             done_flag = 1;
 514           break;
 515         }
 516
 517       if (! PyTuple_Check (item.get ()) || PyTuple_Size (item.get ()) != 2)
 518         {
 519           PyErr_SetString (PyExc_TypeError,
 520                            _("Result of children iterator not a tuple"
 521                              " of two elements."));
 522           gdbpy_print_stack ();
 523           continue;
 524         }
 525       if (! PyArg_ParseTuple (item.get (), "sO", &name, &py_v))
 526         {
 527           /* The user won't necessarily get a stack trace here, so provide
 528              more context.  */
 529           if (gdbpy_print_python_errors_p ())
 530             fprintf_unfiltered (gdb_stderr,
 531                                 _("Bad result from children iterator.\n"));
 532           gdbpy_print_stack ();
 533           continue;
 534         }
 535
 536       /* Print initial "{".  For other elements, there are three
 537          cases:
 538          1. Maps.  Print a "," after each value element.
 539          2. Arrays.  Always print a ",".
 540          3. Other.  Always print a ",".  */
 541       if (i == 0)
 542         {
 543          if (is_py_none)
 544            fputs_filtered ("{", stream);
 545          else
 546            fputs_filtered (" = {", stream);
 547        }
 548
 549       else if (! is_map || i % 2 == 0)
 550         fputs_filtered (pretty ? "," : ", ", stream);
 551
 552       /* In summary mode, we just want to print "= {...}" if there is
 553          a value.  */
 554       if (options->summary)
 555         {
 556           /* This increment tricks the post-loop logic to print what
 557              we want.  */
 558           ++i;
 559           /* Likewise.  */
 560           pretty = 0;
 561           break;
 562         }
 563
 564       if (! is_map || i % 2 == 0)
 565         {
 566           if (pretty)
 567             {
 568               fputs_filtered ("\n", stream);
 569               print_spaces_filtered (2 + 2 * recurse, stream);
 570             }
 571           else
 572             wrap_here (n_spaces (2 + 2 *recurse));
 573         }
 574
 575       if (is_map && i % 2 == 0)
 576         fputs_filtered ("[", stream);
 577       else if (is_array)
 578         {
 579           /* We print the index, not whatever the child method
 580              returned as the name.  */
 581           if (options->print_array_indexes)
 582             fprintf_filtered (stream, "[%d] = ", i);
 583         }
 584       else if (! is_map)
 585         {
 586           fputs_filtered (name, stream);
 587           fputs_filtered (" = ", stream);
 588         }
 589
 590       if (gdbpy_is_lazy_string (py_v))
 591         {
 592           CORE_ADDR addr;
 593           struct type *type;
 594           long length;
 595           gdb::unique_xmalloc_ptr<char> encoding;
 596           struct value_print_options local_opts = *options;
 597
 598           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 599
 600           local_opts.addressprint = 0;
 601           val_print_string (type, encoding.get (), addr, (int) length, stream,
 602                             &local_opts);
 603         }
 604       else if (gdbpy_is_string (py_v))
 605         {
 606           gdb::unique_xmalloc_ptr<char> output;
 607
 608           output = python_string_to_host_string (py_v);
 609           if (!output)
 610             gdbpy_print_stack ();
 611           else
 612             fputs_filtered (output.get (), stream);
 613         }
 614       else
 615         {
 616           struct value *value = convert_value_from_python (py_v);
 617
 618           if (value == NULL)
 619             {
 620               gdbpy_print_stack ();
 621               error (_("Error while executing Python code."));
 622             }
 623           else
 624             common_val_print (value, stream, recurse + 1, options, language);
 625         }
 626
 627       if (is_map && i % 2 == 0)
 628         fputs_filtered ("] = ", stream);
 629     }
 630
 631   if (i)
 632     {
 633       if (!done_flag)
 634         {
 635           if (pretty)
 636             {
 637               fputs_filtered ("\n", stream);
 638               print_spaces_filtered (2 + 2 * recurse, stream);
 639             }
 640           fputs_filtered ("...", stream);
 641         }
 642       if (pretty)
 643         {
 644           fputs_filtered ("\n", stream);
 645           print_spaces_filtered (2 * recurse, stream);
 646         }
 647       fputs_filtered ("}", stream);
 648     }
 649 }
 650
 651 enum ext_lang_rc
 652 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 653                                 struct type *type,
 654                                 LONGEST embedded_offset, CORE_ADDR address,
 655                                 struct ui_file *stream, int recurse,
 656                                 struct value *val,
 657                                 const struct value_print_options *options,
 658                                 const struct language_defn *language)
 659 {
 660   struct gdbarch *gdbarch = get_type_arch (type);
 661   struct value *value;
 662   enum string_repr_result print_result;
 663   const gdb_byte *valaddr = value_contents_for_printing (val);
 664
 665   /* No pretty-printer support for unavailable values.  */
 666   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 667     return EXT_LANG_RC_NOP;
 668
 669   if (!gdb_python_initialized)
 670     return EXT_LANG_RC_NOP;
 671
 672   gdbpy_enter enter_py (gdbarch, language);
 673
 674   /* Instantiate the printer.  */
 675   value = value_from_component (val, type, embedded_offset);
 676
 677   gdbpy_ref val_obj (value_to_value_object (value));
 678   if (val_obj == NULL)
 679     {
 680       print_stack_unless_memory_error (stream);
 681       return EXT_LANG_RC_ERROR;
 682     }
 683
 684   /* Find the constructor.  */
 685   gdbpy_ref printer (find_pretty_printer (val_obj.get ()));
 686   if (printer == NULL)
 687     {
 688       print_stack_unless_memory_error (stream);
 689       return EXT_LANG_RC_ERROR;
 690     }
 691
 692   if (printer == Py_None)
 693     return EXT_LANG_RC_NOP;
 694
 695   /* If we are printing a map, we want some special formatting.  */
 696   gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
 697
 698   /* Print the section */
 699   print_result = print_string_repr (printer.get (), hint.get (), stream,
 700                                     recurse, options, language, gdbarch);
 701   if (print_result != string_repr_error)
 702     print_children (printer.get (), hint.get (), stream, recurse, options,
 703                     language, print_result == string_repr_none);
 704
 705   if (PyErr_Occurred ())
 706     print_stack_unless_memory_error (stream);
 707   return EXT_LANG_RC_OK;
 708 }
 709
 710
 711 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 712    print object.  It must have a 'to_string' method (but this is
 713    checked by varobj, not here) which takes no arguments and
 714    returns a string.  The printer will return a value and in the case
 715    of a Python string being returned, this function will return a
 716    PyObject containing the string.  For any other type, *REPLACEMENT is
 717    set to the replacement value and this function returns NULL.  On
 718    error, *REPLACEMENT is set to NULL and this function also returns
 719    NULL.  */
 720 PyObject *
 721 apply_varobj_pretty_printer (PyObject *printer_obj,
 722                              struct value **replacement,
 723                              struct ui_file *stream)
 724 {
 725   PyObject *py_str = NULL;
 726
 727   *replacement = NULL;
 728   py_str = pretty_print_one_value (printer_obj, replacement);
 729
 730   if (*replacement == NULL && py_str == NULL)
 731     print_stack_unless_memory_error (stream);
 732
 733   return py_str;
 734 }
 735
 736 /* Find a pretty-printer object for the varobj module.  Returns a new
 737    reference to the object if successful; returns NULL if not.  VALUE
 738    is the value for which a printer tests to determine if it
 739    can pretty-print the value.  */
 740 PyObject *
 741 gdbpy_get_varobj_pretty_printer (struct value *value)
 742 {
 743   TRY
 744     {
 745       value = value_copy (value);
 746     }
 747   CATCH (except, RETURN_MASK_ALL)
 748     {
 749       GDB_PY_HANDLE_EXCEPTION (except);
 750     }
 751   END_CATCH
 752
 753   gdbpy_ref val_obj (value_to_value_object (value));
 754   if (val_obj == NULL)
 755     return NULL;
 756
 757   return find_pretty_printer (val_obj.get ());
 758 }
 759
 760 /* A Python function which wraps find_pretty_printer and instantiates
 761    the resulting class.  This accepts a Value argument and returns a
 762    pretty printer instance, or None.  This function is useful as an
 763    argument to the MI command -var-set-visualizer.  */
 764 PyObject *
 765 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 766 {
 767   PyObject *val_obj;
 768   PyObject *cons;
 769   struct value *value;
 770
 771   if (! PyArg_ParseTuple (args, "O", &val_obj))
 772     return NULL;
 773   value = value_object_to_value (val_obj);
 774   if (! value)
 775     {
 776       PyErr_SetString (PyExc_TypeError,
 777                        _("Argument must be a gdb.Value."));
 778       return NULL;
 779     }
 780
 781   cons = find_pretty_printer (val_obj);
 782   return cons;
 783 }