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| 53 | <H2><A NAME="SECTION004110000000000000000"> |
| 54 | 2.1.1 Adding data and methods to the Basic example</A> |
| 55 | </H2> |
| 56 | |
| 57 | <P> |
| 58 | Let's expend the basic example to add some data and methods. Let's |
| 59 | also make the type usable as a base class. We'll create |
| 60 | a new module, <tt class="module">noddy2</tt> that adds these capabilities: |
| 61 | |
| 62 | <P> |
| 63 | <div class="verbatim"> |
| 64 | <pre>#include <Python.h> |
| 65 | #include "structmember.h" |
| 66 | |
| 67 | typedef struct { |
| 68 | PyObject_HEAD |
| 69 | PyObject *first; /* first name */ |
| 70 | PyObject *last; /* last name */ |
| 71 | int number; |
| 72 | } Noddy; |
| 73 | |
| 74 | static void |
| 75 | Noddy_dealloc(Noddy* self) |
| 76 | { |
| 77 | Py_XDECREF(self->first); |
| 78 | Py_XDECREF(self->last); |
| 79 | self->ob_type->tp_free((PyObject*)self); |
| 80 | } |
| 81 | |
| 82 | static PyObject * |
| 83 | Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) |
| 84 | { |
| 85 | Noddy *self; |
| 86 | |
| 87 | self = (Noddy *)type->tp_alloc(type, 0); |
| 88 | if (self != NULL) { |
| 89 | self->first = PyString_FromString(""); |
| 90 | if (self->first == NULL) |
| 91 | { |
| 92 | Py_DECREF(self); |
| 93 | return NULL; |
| 94 | } |
| 95 | |
| 96 | self->last = PyString_FromString(""); |
| 97 | if (self->last == NULL) |
| 98 | { |
| 99 | Py_DECREF(self); |
| 100 | return NULL; |
| 101 | } |
| 102 | |
| 103 | self->number = 0; |
| 104 | } |
| 105 | |
| 106 | return (PyObject *)self; |
| 107 | } |
| 108 | |
| 109 | static int |
| 110 | Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) |
| 111 | { |
| 112 | PyObject *first=NULL, *last=NULL, *tmp; |
| 113 | |
| 114 | static char *kwlist[] = {"first", "last", "number", NULL}; |
| 115 | |
| 116 | if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist, |
| 117 | &first, &last, |
| 118 | &self->number)) |
| 119 | return -1; |
| 120 | |
| 121 | if (first) { |
| 122 | tmp = self->first; |
| 123 | Py_INCREF(first); |
| 124 | self->first = first; |
| 125 | Py_XDECREF(tmp); |
| 126 | } |
| 127 | |
| 128 | if (last) { |
| 129 | tmp = self->last; |
| 130 | Py_INCREF(last); |
| 131 | self->last = last; |
| 132 | Py_XDECREF(tmp); |
| 133 | } |
| 134 | |
| 135 | return 0; |
| 136 | } |
| 137 | |
| 138 | static PyMemberDef Noddy_members[] = { |
| 139 | {"first", T_OBJECT_EX, offsetof(Noddy, first), 0, |
| 140 | "first name"}, |
| 141 | {"last", T_OBJECT_EX, offsetof(Noddy, last), 0, |
| 142 | "last name"}, |
| 143 | {"number", T_INT, offsetof(Noddy, number), 0, |
| 144 | "noddy number"}, |
| 145 | {NULL} /* Sentinel */ |
| 146 | }; |
| 147 | |
| 148 | static PyObject * |
| 149 | Noddy_name(Noddy* self) |
| 150 | { |
| 151 | static PyObject *format = NULL; |
| 152 | PyObject *args, *result; |
| 153 | |
| 154 | if (format == NULL) { |
| 155 | format = PyString_FromString("%s %s"); |
| 156 | if (format == NULL) |
| 157 | return NULL; |
| 158 | } |
| 159 | |
| 160 | if (self->first == NULL) { |
| 161 | PyErr_SetString(PyExc_AttributeError, "first"); |
| 162 | return NULL; |
| 163 | } |
| 164 | |
| 165 | if (self->last == NULL) { |
| 166 | PyErr_SetString(PyExc_AttributeError, "last"); |
| 167 | return NULL; |
| 168 | } |
| 169 | |
| 170 | args = Py_BuildValue("OO", self->first, self->last); |
| 171 | if (args == NULL) |
| 172 | return NULL; |
| 173 | |
| 174 | result = PyString_Format(format, args); |
| 175 | Py_DECREF(args); |
| 176 | |
| 177 | return result; |
| 178 | } |
| 179 | |
| 180 | static PyMethodDef Noddy_methods[] = { |
| 181 | {"name", (PyCFunction)Noddy_name, METH_NOARGS, |
| 182 | "Return the name, combining the first and last name" |
| 183 | }, |
| 184 | {NULL} /* Sentinel */ |
| 185 | }; |
| 186 | |
| 187 | static PyTypeObject NoddyType = { |
| 188 | PyObject_HEAD_INIT(NULL) |
| 189 | 0, /*ob_size*/ |
| 190 | "noddy.Noddy", /*tp_name*/ |
| 191 | sizeof(Noddy), /*tp_basicsize*/ |
| 192 | 0, /*tp_itemsize*/ |
| 193 | (destructor)Noddy_dealloc, /*tp_dealloc*/ |
| 194 | 0, /*tp_print*/ |
| 195 | 0, /*tp_getattr*/ |
| 196 | 0, /*tp_setattr*/ |
| 197 | 0, /*tp_compare*/ |
| 198 | 0, /*tp_repr*/ |
| 199 | 0, /*tp_as_number*/ |
| 200 | 0, /*tp_as_sequence*/ |
| 201 | 0, /*tp_as_mapping*/ |
| 202 | 0, /*tp_hash */ |
| 203 | 0, /*tp_call*/ |
| 204 | 0, /*tp_str*/ |
| 205 | 0, /*tp_getattro*/ |
| 206 | 0, /*tp_setattro*/ |
| 207 | 0, /*tp_as_buffer*/ |
| 208 | Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/ |
| 209 | "Noddy objects", /* tp_doc */ |
| 210 | 0, /* tp_traverse */ |
| 211 | 0, /* tp_clear */ |
| 212 | 0, /* tp_richcompare */ |
| 213 | 0, /* tp_weaklistoffset */ |
| 214 | 0, /* tp_iter */ |
| 215 | 0, /* tp_iternext */ |
| 216 | Noddy_methods, /* tp_methods */ |
| 217 | Noddy_members, /* tp_members */ |
| 218 | 0, /* tp_getset */ |
| 219 | 0, /* tp_base */ |
| 220 | 0, /* tp_dict */ |
| 221 | 0, /* tp_descr_get */ |
| 222 | 0, /* tp_descr_set */ |
| 223 | 0, /* tp_dictoffset */ |
| 224 | (initproc)Noddy_init, /* tp_init */ |
| 225 | 0, /* tp_alloc */ |
| 226 | Noddy_new, /* tp_new */ |
| 227 | }; |
| 228 | |
| 229 | static PyMethodDef module_methods[] = { |
| 230 | {NULL} /* Sentinel */ |
| 231 | }; |
| 232 | |
| 233 | #ifndef PyMODINIT_FUNC /* declarations for DLL import/export */ |
| 234 | #define PyMODINIT_FUNC void |
| 235 | #endif |
| 236 | PyMODINIT_FUNC |
| 237 | initnoddy2(void) |
| 238 | { |
| 239 | PyObject* m; |
| 240 | |
| 241 | if (PyType_Ready(&NoddyType) < 0) |
| 242 | return; |
| 243 | |
| 244 | m = Py_InitModule3("noddy2", module_methods, |
| 245 | "Example module that creates an extension type."); |
| 246 | |
| 247 | if (m == NULL) |
| 248 | return; |
| 249 | |
| 250 | Py_INCREF(&NoddyType); |
| 251 | PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType); |
| 252 | } |
| 253 | </pre> |
| 254 | <div class="footer"> |
| 255 | <a href="noddy2.txt" type="text/plain">Download as text (original file name: <span class="file">noddy2.c</span>).</a> |
| 256 | </div></div> |
| 257 | |
| 258 | <P> |
| 259 | This version of the module has a number of changes. |
| 260 | |
| 261 | <P> |
| 262 | We've added an extra include: |
| 263 | |
| 264 | <P> |
| 265 | <div class="verbatim"><pre> |
| 266 | #include "structmember.h" |
| 267 | </pre></div> |
| 268 | |
| 269 | <P> |
| 270 | This include provides declarations that we use to handle attributes, |
| 271 | as described a bit later. |
| 272 | |
| 273 | <P> |
| 274 | The name of the <tt class="class">Noddy</tt> object structure has been shortened to |
| 275 | <tt class="class">Noddy</tt>. The type object name has been shortened to |
| 276 | <tt class="class">NoddyType</tt>. |
| 277 | |
| 278 | <P> |
| 279 | The <tt class="class">Noddy</tt> type now has three data attributes, <var>first</var>, |
| 280 | <var>last</var>, and <var>number</var>. The <var>first</var> and <var>last</var> |
| 281 | variables are Python strings containing first and last names. The |
| 282 | <var>number</var> attribute is an integer. |
| 283 | |
| 284 | <P> |
| 285 | The object structure is updated accordingly: |
| 286 | |
| 287 | <P> |
| 288 | <div class="verbatim"><pre> |
| 289 | typedef struct { |
| 290 | PyObject_HEAD |
| 291 | PyObject *first; |
| 292 | PyObject *last; |
| 293 | int number; |
| 294 | } Noddy; |
| 295 | </pre></div> |
| 296 | |
| 297 | <P> |
| 298 | Because we now have data to manage, we have to be more careful about |
| 299 | object allocation and deallocation. At a minimum, we need a |
| 300 | deallocation method: |
| 301 | |
| 302 | <P> |
| 303 | <div class="verbatim"><pre> |
| 304 | static void |
| 305 | Noddy_dealloc(Noddy* self) |
| 306 | { |
| 307 | Py_XDECREF(self->first); |
| 308 | Py_XDECREF(self->last); |
| 309 | self->ob_type->tp_free((PyObject*)self); |
| 310 | } |
| 311 | </pre></div> |
| 312 | |
| 313 | <P> |
| 314 | which is assigned to the <tt class="member">tp_dealloc</tt> member: |
| 315 | |
| 316 | <P> |
| 317 | <div class="verbatim"><pre> |
| 318 | (destructor)Noddy_dealloc, /*tp_dealloc*/ |
| 319 | </pre></div> |
| 320 | |
| 321 | <P> |
| 322 | This method decrements the reference counts of the two Python |
| 323 | attributes. We use <tt class="cfunction">Py_XDECREF()</tt> here because the |
| 324 | <tt class="member">first</tt> and <tt class="member">last</tt> members could be <tt class="constant">NULL</tt>. It then |
| 325 | calls the <tt class="member">tp_free</tt> member of the object's type to free the |
| 326 | object's memory. Note that the object's type might not be |
| 327 | <tt class="class">NoddyType</tt>, because the object may be an instance of a |
| 328 | subclass. |
| 329 | |
| 330 | <P> |
| 331 | We want to make sure that the first and last names are initialized to |
| 332 | empty strings, so we provide a new method: |
| 333 | |
| 334 | <P> |
| 335 | <div class="verbatim"><pre> |
| 336 | static PyObject * |
| 337 | Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) |
| 338 | { |
| 339 | Noddy *self; |
| 340 | |
| 341 | self = (Noddy *)type->tp_alloc(type, 0); |
| 342 | if (self != NULL) { |
| 343 | self->first = PyString_FromString(""); |
| 344 | if (self->first == NULL) |
| 345 | { |
| 346 | Py_DECREF(self); |
| 347 | return NULL; |
| 348 | } |
| 349 | |
| 350 | self->last = PyString_FromString(""); |
| 351 | if (self->last == NULL) |
| 352 | { |
| 353 | Py_DECREF(self); |
| 354 | return NULL; |
| 355 | } |
| 356 | |
| 357 | self->number = 0; |
| 358 | } |
| 359 | |
| 360 | return (PyObject *)self; |
| 361 | } |
| 362 | </pre></div> |
| 363 | |
| 364 | <P> |
| 365 | and install it in the <tt class="member">tp_new</tt> member: |
| 366 | |
| 367 | <P> |
| 368 | <div class="verbatim"><pre> |
| 369 | Noddy_new, /* tp_new */ |
| 370 | </pre></div> |
| 371 | |
| 372 | <P> |
| 373 | The new member is responsible for creating (as opposed to |
| 374 | initializing) objects of the type. It is exposed in Python as the |
| 375 | <tt class="method">__new__()</tt> method. See the paper titled ``Unifying types and |
| 376 | classes in Python'' for a detailed discussion of the <tt class="method">__new__()</tt> |
| 377 | method. One reason to implement a new method is to assure the initial |
| 378 | values of instance variables. In this case, we use the new method to |
| 379 | make sure that the initial values of the members <tt class="member">first</tt> and |
| 380 | <tt class="member">last</tt> are not <tt class="constant">NULL</tt>. If we didn't care whether the initial |
| 381 | values were <tt class="constant">NULL</tt>, we could have used <tt class="cfunction">PyType_GenericNew()</tt> as |
| 382 | our new method, as we did before. <tt class="cfunction">PyType_GenericNew()</tt> |
| 383 | initializes all of the instance variable members to <tt class="constant">NULL</tt>. |
| 384 | |
| 385 | <P> |
| 386 | The new method is a static method that is passed the type being |
| 387 | instantiated and any arguments passed when the type was called, |
| 388 | and that returns the new object created. New methods always accept |
| 389 | positional and keyword arguments, but they often ignore the arguments, |
| 390 | leaving the argument handling to initializer methods. Note that if the |
| 391 | type supports subclassing, the type passed may not be the type being |
| 392 | defined. The new method calls the tp_alloc slot to allocate memory. |
| 393 | We don't fill the <tt class="member">tp_alloc</tt> slot ourselves. Rather |
| 394 | <tt class="cfunction">PyType_Ready()</tt> fills it for us by inheriting it from our |
| 395 | base class, which is <tt class="class">object</tt> by default. Most types use the |
| 396 | default allocation. |
| 397 | |
| 398 | <P> |
| 399 | <span class="note"><b class="label">Note:</b> |
| 400 | If you are creating a co-operative <tt class="member">tp_new</tt> (one that |
| 401 | calls a base type's <tt class="member">tp_new</tt> or <tt class="method">__new__</tt>), you |
| 402 | must <em>not</em> try to determine what method to call using |
| 403 | method resolution order at runtime. Always statically determine |
| 404 | what type you are going to call, and call its <tt class="member">tp_new</tt> |
| 405 | directly, or via <code>type->tp_base->tp_new</code>. If you do |
| 406 | not do this, Python subclasses of your type that also inherit |
| 407 | from other Python-defined classes may not work correctly. |
| 408 | (Specifically, you may not be able to create instances of |
| 409 | such subclasses without getting a <tt class="exception">TypeError</tt>.)</span> |
| 410 | |
| 411 | <P> |
| 412 | We provide an initialization function: |
| 413 | |
| 414 | <P> |
| 415 | <div class="verbatim"><pre> |
| 416 | static int |
| 417 | Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) |
| 418 | { |
| 419 | PyObject *first=NULL, *last=NULL, *tmp; |
| 420 | |
| 421 | static char *kwlist[] = {"first", "last", "number", NULL}; |
| 422 | |
| 423 | if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist, |
| 424 | &first, &last, |
| 425 | &self->number)) |
| 426 | return -1; |
| 427 | |
| 428 | if (first) { |
| 429 | tmp = self->first; |
| 430 | Py_INCREF(first); |
| 431 | self->first = first; |
| 432 | Py_XDECREF(tmp); |
| 433 | } |
| 434 | |
| 435 | if (last) { |
| 436 | tmp = self->last; |
| 437 | Py_INCREF(last); |
| 438 | self->last = last; |
| 439 | Py_XDECREF(tmp); |
| 440 | } |
| 441 | |
| 442 | return 0; |
| 443 | } |
| 444 | </pre></div> |
| 445 | |
| 446 | <P> |
| 447 | by filling the <tt class="member">tp_init</tt> slot. |
| 448 | |
| 449 | <P> |
| 450 | <div class="verbatim"><pre> |
| 451 | (initproc)Noddy_init, /* tp_init */ |
| 452 | </pre></div> |
| 453 | |
| 454 | <P> |
| 455 | The <tt class="member">tp_init</tt> slot is exposed in Python as the |
| 456 | <tt class="method">__init__()</tt> method. It is used to initialize an object after |
| 457 | it's created. Unlike the new method, we can't guarantee that the |
| 458 | initializer is called. The initializer isn't called when unpickling |
| 459 | objects and it can be overridden. Our initializer accepts arguments |
| 460 | to provide initial values for our instance. Initializers always accept |
| 461 | positional and keyword arguments. |
| 462 | |
| 463 | <P> |
| 464 | Initializers can be called multiple times. Anyone can call the |
| 465 | <tt class="method">__init__()</tt> method on our objects. For this reason, we have |
| 466 | to be extra careful when assigning the new values. We might be |
| 467 | tempted, for example to assign the <tt class="member">first</tt> member like this: |
| 468 | |
| 469 | <P> |
| 470 | <div class="verbatim"><pre> |
| 471 | if (first) { |
| 472 | Py_XDECREF(self->first); |
| 473 | Py_INCREF(first); |
| 474 | self->first = first; |
| 475 | } |
| 476 | </pre></div> |
| 477 | |
| 478 | <P> |
| 479 | But this would be risky. Our type doesn't restrict the type of the |
| 480 | <tt class="member">first</tt> member, so it could be any kind of object. It could |
| 481 | have a destructor that causes code to be executed that tries to |
| 482 | access the <tt class="member">first</tt> member. To be paranoid and protect |
| 483 | ourselves against this possibility, we almost always reassign members |
| 484 | before decrementing their reference counts. When don't we have to do |
| 485 | this? |
| 486 | |
| 487 | <UL> |
| 488 | <LI>when we absolutely know that the reference count is greater than |
| 489 | 1 |
| 490 | </LI> |
| 491 | <LI>when we know that deallocation of the object<A NAME="tex2html5" |
| 492 | HREF="#foot1098"><SUP>2.1</SUP></A> will not cause any |
| 493 | calls back into our type's code |
| 494 | </LI> |
| 495 | <LI>when decrementing a reference count in a <tt class="member">tp_dealloc</tt> |
| 496 | handler when garbage-collections is not supported<A NAME="tex2html6" |
| 497 | HREF="#foot1418"><SUP>2.2</SUP></A> |
| 498 | </LI> |
| 499 | <LI> |
| 500 | </LI> |
| 501 | </UL> |
| 502 | |
| 503 | <P> |
| 504 | We want to want to expose our instance variables as attributes. There |
| 505 | are a number of ways to do that. The simplest way is to define member |
| 506 | definitions: |
| 507 | |
| 508 | <P> |
| 509 | <div class="verbatim"><pre> |
| 510 | static PyMemberDef Noddy_members[] = { |
| 511 | {"first", T_OBJECT_EX, offsetof(Noddy, first), 0, |
| 512 | "first name"}, |
| 513 | {"last", T_OBJECT_EX, offsetof(Noddy, last), 0, |
| 514 | "last name"}, |
| 515 | {"number", T_INT, offsetof(Noddy, number), 0, |
| 516 | "noddy number"}, |
| 517 | {NULL} /* Sentinel */ |
| 518 | }; |
| 519 | </pre></div> |
| 520 | |
| 521 | <P> |
| 522 | and put the definitions in the <tt class="member">tp_members</tt> slot: |
| 523 | |
| 524 | <P> |
| 525 | <div class="verbatim"><pre> |
| 526 | Noddy_members, /* tp_members */ |
| 527 | </pre></div> |
| 528 | |
| 529 | <P> |
| 530 | Each member definition has a member name, type, offset, access flags |
| 531 | and documentation string. See the ``Generic Attribute Management'' |
| 532 | section below for details. |
| 533 | |
| 534 | <P> |
| 535 | A disadvantage of this approach is that it doesn't provide a way to |
| 536 | restrict the types of objects that can be assigned to the Python |
| 537 | attributes. We expect the first and last names to be strings, but any |
| 538 | Python objects can be assigned. Further, the attributes can be |
| 539 | deleted, setting the C pointers to <tt class="constant">NULL</tt>. Even though we can make |
| 540 | sure the members are initialized to non-<tt class="constant">NULL</tt> values, the members can |
| 541 | be set to <tt class="constant">NULL</tt> if the attributes are deleted. |
| 542 | |
| 543 | <P> |
| 544 | We define a single method, <tt class="method">name</tt>, that outputs the objects |
| 545 | name as the concatenation of the first and last names. |
| 546 | |
| 547 | <P> |
| 548 | <div class="verbatim"><pre> |
| 549 | static PyObject * |
| 550 | Noddy_name(Noddy* self) |
| 551 | { |
| 552 | static PyObject *format = NULL; |
| 553 | PyObject *args, *result; |
| 554 | |
| 555 | if (format == NULL) { |
| 556 | format = PyString_FromString("%s %s"); |
| 557 | if (format == NULL) |
| 558 | return NULL; |
| 559 | } |
| 560 | |
| 561 | if (self->first == NULL) { |
| 562 | PyErr_SetString(PyExc_AttributeError, "first"); |
| 563 | return NULL; |
| 564 | } |
| 565 | |
| 566 | if (self->last == NULL) { |
| 567 | PyErr_SetString(PyExc_AttributeError, "last"); |
| 568 | return NULL; |
| 569 | } |
| 570 | |
| 571 | args = Py_BuildValue("OO", self->first, self->last); |
| 572 | if (args == NULL) |
| 573 | return NULL; |
| 574 | |
| 575 | result = PyString_Format(format, args); |
| 576 | Py_DECREF(args); |
| 577 | |
| 578 | return result; |
| 579 | } |
| 580 | </pre></div> |
| 581 | |
| 582 | <P> |
| 583 | The method is implemented as a C function that takes a <tt class="class">Noddy</tt> (or |
| 584 | <tt class="class">Noddy</tt> subclass) instance as the first argument. Methods |
| 585 | always take an instance as the first argument. Methods often take |
| 586 | positional and keyword arguments as well, but in this cased we don't |
| 587 | take any and don't need to accept a positional argument tuple or |
| 588 | keyword argument dictionary. This method is equivalent to the Python |
| 589 | method: |
| 590 | |
| 591 | <P> |
| 592 | <div class="verbatim"><pre> |
| 593 | def name(self): |
| 594 | return "%s %s" % (self.first, self.last) |
| 595 | </pre></div> |
| 596 | |
| 597 | <P> |
| 598 | Note that we have to check for the possibility that our <tt class="member">first</tt> |
| 599 | and <tt class="member">last</tt> members are <tt class="constant">NULL</tt>. This is because they can be |
| 600 | deleted, in which case they are set to <tt class="constant">NULL</tt>. It would be better to |
| 601 | prevent deletion of these attributes and to restrict the attribute |
| 602 | values to be strings. We'll see how to do that in the next section. |
| 603 | |
| 604 | <P> |
| 605 | Now that we've defined the method, we need to create an array of |
| 606 | method definitions: |
| 607 | |
| 608 | <P> |
| 609 | <div class="verbatim"><pre> |
| 610 | static PyMethodDef Noddy_methods[] = { |
| 611 | {"name", (PyCFunction)Noddy_name, METH_NOARGS, |
| 612 | "Return the name, combining the first and last name" |
| 613 | }, |
| 614 | {NULL} /* Sentinel */ |
| 615 | }; |
| 616 | </pre></div> |
| 617 | |
| 618 | <P> |
| 619 | and assign them to the <tt class="member">tp_methods</tt> slot: |
| 620 | |
| 621 | <P> |
| 622 | <div class="verbatim"><pre> |
| 623 | Noddy_methods, /* tp_methods */ |
| 624 | </pre></div> |
| 625 | |
| 626 | <P> |
| 627 | Note that we used the <tt class="constant">METH_NOARGS</tt> flag to indicate that the |
| 628 | method is passed no arguments. |
| 629 | |
| 630 | <P> |
| 631 | Finally, we'll make our type usable as a base class. We've written |
| 632 | our methods carefully so far so that they don't make any assumptions |
| 633 | about the type of the object being created or used, so all we need to |
| 634 | do is to add the <tt class="constant">Py_TPFLAGS_BASETYPE</tt> to our class flag |
| 635 | definition: |
| 636 | |
| 637 | <P> |
| 638 | <div class="verbatim"><pre> |
| 639 | Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/ |
| 640 | </pre></div> |
| 641 | |
| 642 | <P> |
| 643 | We rename <tt class="cfunction">initnoddy()</tt> to <tt class="cfunction">initnoddy2()</tt> |
| 644 | and update the module name passed to <tt class="cfunction">Py_InitModule3()</tt>. |
| 645 | |
| 646 | <P> |
| 647 | Finally, we update our <span class="file">setup.py</span> file to build the new module: |
| 648 | |
| 649 | <P> |
| 650 | <div class="verbatim"><pre> |
| 651 | from distutils.core import setup, Extension |
| 652 | setup(name="noddy", version="1.0", |
| 653 | ext_modules=[ |
| 654 | Extension("noddy", ["noddy.c"]), |
| 655 | Extension("noddy2", ["noddy2.c"]), |
| 656 | ]) |
| 657 | </pre></div> |
| 658 | |
| 659 | <P> |
| 660 | <BR><HR><H4>Footnotes</H4> |
| 661 | <DL> |
| 662 | <DT><A NAME="foot1098">... object</A><A |
| 663 | HREF="node22.html#tex2html5"><SUP>2.1</SUP></A></DT> |
| 664 | <DD>This is |
| 665 | true when we know that the object is a basic type, like a string or |
| 666 | a float |
| 667 | |
| 668 | </DD> |
| 669 | <DT><A NAME="foot1418">... supported</A><A |
| 670 | HREF="node22.html#tex2html6"><SUP>2.2</SUP></A></DT> |
| 671 | <DD>We relied |
| 672 | on this in the <tt class="member">tp_dealloc</tt> handler in this example, because |
| 673 | our type doesn't support garbage collection. Even if a type supports |
| 674 | garbage collection, there are calls that can be made to ``untrack'' |
| 675 | the object from garbage collection, however, these calls are |
| 676 | advanced and not covered here. |
| 677 | |
| 678 | </DD> |
| 679 | </DL> |
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| 713 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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