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# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001 Python Software Foundation
# This file is distributed under the same license as the Python package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
# Translators:
# Bhuvansh Kataria, 2026
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: Python 3.15\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2026-10-31 18:01+0000\n"
"PO-Revision-Date: 2025-09-16 00:00+0000\n"
"Last-Translator: Bhuvansh Kataria, 2026\n"
"Language-Team: Panjabi (Punjabi) (https://app.transifex.com/python-doc/teams/"
"5390/pa/)\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Language: pa\n"
"Plural-Forms: nplurals=2; plural=(n != 1);\n"
msgid "Defining Extension Types: Tutorial"
msgstr ""
msgid ""
"Python allows the writer of a C extension module to define new types that "
"can be manipulated from Python code, much like the built-in :class:`str` "
"and :class:`list` types. The code for all extension types follows a "
"pattern, but there are some details that you need to understand before you "
"can get started. This document is a gentle introduction to the topic."
msgstr ""
msgid "The Basics"
msgstr ""
msgid ""
"The :term:`CPython` runtime sees all Python objects as variables of "
"type :c:expr:`PyObject*`, which serves as a \"base type\" for all Python "
"objects. The :c:type:`PyObject` structure itself only contains the "
"object's :term:`reference count` and a pointer to the object's \"type "
"object\". This is where the action is; the type object determines which (C) "
"functions get called by the interpreter when, for instance, an attribute "
"gets looked up on an object, a method called, or it is multiplied by another "
"object. These C functions are called \"type methods\"."
msgstr ""
msgid ""
"So, if you want to define a new extension type, you need to create a new "
"type object."
msgstr ""
msgid ""
"This sort of thing can only be explained by example, so here's a minimal, "
"but complete, module that defines a new type named :class:`!Custom` inside a "
"C extension module :mod:`!custom`:"
msgstr ""
msgid ""
"What we're showing here is the traditional way of defining *static* "
"extension types. It should be adequate for most uses. The C API also "
"allows defining heap-allocated extension types using "
"the :c:func:`PyType_FromSpec` function, which isn't covered in this tutorial."
msgstr ""
msgid ""
"#define PY_SSIZE_T_CLEAN\n"
"#include <Python.h>\n"
"\n"
"typedef struct {\n"
" PyObject_HEAD\n"
" /* Type-specific fields go here. */\n"
"} CustomObject;\n"
"\n"
"static PyTypeObject CustomType = {\n"
" .ob_base = PyVarObject_HEAD_INIT(NULL, 0)\n"
" .tp_name = \"custom.Custom\",\n"
" .tp_doc = PyDoc_STR(\"Custom objects\"),\n"
" .tp_basicsize = sizeof(CustomObject),\n"
" .tp_itemsize = 0,\n"
" .tp_flags = Py_TPFLAGS_DEFAULT,\n"
" .tp_new = PyType_GenericNew,\n"
"};\n"
"\n"
"static int\n"
"custom_module_exec(PyObject *m)\n"
"{\n"
" if (PyType_Ready(&CustomType) < 0) {\n"
" return -1;\n"
" }\n"
"\n"
" if (PyModule_AddObjectRef(m, \"Custom\", (PyObject *) &CustomType) < 0) "
"{\n"
" return -1;\n"
" }\n"
"\n"
" return 0;\n"
"}\n"
"\n"
"static PyModuleDef_Slot custom_module_slots[] = {\n"
" {Py_mod_exec, custom_module_exec},\n"
" // Just use this while using static types\n"
" {Py_mod_multiple_interpreters, "
"Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED},\n"
" {0, NULL}\n"
"};\n"
"\n"
"static PyModuleDef custom_module = {\n"
" .m_base = PyModuleDef_HEAD_INIT,\n"
" .m_name = \"custom\",\n"
" .m_doc = \"Example module that creates an extension type.\",\n"
" .m_size = 0,\n"
" .m_slots = custom_module_slots,\n"
"};\n"
"\n"
"PyMODINIT_FUNC\n"
"PyInit_custom(void)\n"
"{\n"
" return PyModuleDef_Init(&custom_module);\n"
"}\n"
msgstr ""
msgid ""
"Now that's quite a bit to take in at once, but hopefully bits will seem "
"familiar from the previous chapter. This file defines three things:"
msgstr ""
msgid ""
"What a :class:`!Custom` **object** contains: this is the ``CustomObject`` "
"struct, which is allocated once for each :class:`!Custom` instance."
msgstr ""
msgid ""
"How the :class:`!Custom` **type** behaves: this is the ``CustomType`` "
"struct, which defines a set of flags and function pointers that the "
"interpreter inspects when specific operations are requested."
msgstr ""
msgid ""
"How to define and execute the :mod:`!custom` module: this is the "
"``PyInit_custom`` function and the associated ``custom_module`` struct for "
"defining the module, and the ``custom_module_exec`` function to set up a "
"fresh module object."
msgstr ""
msgid "The first bit is::"
msgstr ""
msgid ""
"typedef struct {\n"
" PyObject_HEAD\n"
"} CustomObject;"
msgstr ""
msgid ""
"This is what a Custom object will contain. ``PyObject_HEAD`` is mandatory "
"at the start of each object struct and defines a field called ``ob_base`` of "
"type :c:type:`PyObject`, containing a pointer to a type object and a "
"reference count (these can be accessed using the macros :c:macro:`Py_TYPE` "
"and :c:macro:`Py_REFCNT` respectively). The reason for the macro is to "
"abstract away the layout and to enable additional fields in :ref:`debug "
"builds <debug-build>`."
msgstr ""
msgid ""
"There is no semicolon above after the :c:macro:`PyObject_HEAD` macro. Be "
"wary of adding one by accident: some compilers will complain."
msgstr ""
msgid ""
"Of course, objects generally store additional data besides the standard "
"``PyObject_HEAD`` boilerplate; for example, here is the definition for "
"standard Python floats::"
msgstr ""
msgid ""
"typedef struct {\n"
" PyObject_HEAD\n"
" double ob_fval;\n"
"} PyFloatObject;"
msgstr ""
msgid "The second bit is the definition of the type object. ::"
msgstr ""
msgid ""
"static PyTypeObject CustomType = {\n"
" .ob_base = PyVarObject_HEAD_INIT(NULL, 0)\n"
" .tp_name = \"custom.Custom\",\n"
" .tp_doc = PyDoc_STR(\"Custom objects\"),\n"
" .tp_basicsize = sizeof(CustomObject),\n"
" .tp_itemsize = 0,\n"
" .tp_flags = Py_TPFLAGS_DEFAULT,\n"
" .tp_new = PyType_GenericNew,\n"
"};"
msgstr ""
msgid ""
"We recommend using C99-style designated initializers as above, to avoid "
"listing all the :c:type:`PyTypeObject` fields that you don't care about and "
"also to avoid caring about the fields' declaration order."
msgstr ""
msgid ""
"The actual definition of :c:type:`PyTypeObject` in :file:`object.h` has many "
"more :ref:`fields <type-structs>` than the definition above. The remaining "
"fields will be filled with zeros by the C compiler, and it's common practice "
"to not specify them explicitly unless you need them."
msgstr ""
msgid "We're going to pick it apart, one field at a time::"
msgstr ""
msgid ".ob_base = PyVarObject_HEAD_INIT(NULL, 0)"
msgstr ""
msgid ""
"This line is mandatory boilerplate to initialize the ``ob_base`` field "
"mentioned above. ::"
msgstr ""
msgid ".tp_name = \"custom.Custom\","
msgstr ""
msgid ""
"The name of our type. This will appear in the default textual "
"representation of our objects and in some error messages, for example:"
msgstr ""
msgid ""
">>> \"\" + custom.Custom()\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: can only concatenate str (not \"custom.Custom\") to str"
msgstr ""
msgid ""
"Note that the name is a dotted name that includes both the module name and "
"the name of the type within the module. The module in this case is :mod:`!"
"custom` and the type is :class:`!Custom`, so we set the type name "
"to :class:`!custom.Custom`. Using the real dotted import path is important "
"to make your type compatible with the :mod:`pydoc` and :mod:`pickle` "
"modules. ::"
msgstr ""
msgid ""
".tp_basicsize = sizeof(CustomObject),\n"
".tp_itemsize = 0,"
msgstr ""
msgid ""
"This is so that Python knows how much memory to allocate when creating "
"new :class:`!Custom` instances. :c:member:`~PyTypeObject.tp_itemsize` is "
"only used for variable-sized objects and should otherwise be zero."
msgstr ""
msgid ""
"If you want your type to be subclassable from Python, and your type has the "
"same :c:member:`~PyTypeObject.tp_basicsize` as its base type, you may have "
"problems with multiple inheritance. A Python subclass of your type will "
"have to list your type first in its :attr:`~type.__bases__`, or else it will "
"not be able to call your type's :meth:`~object.__new__` method without "
"getting an error. You can avoid this problem by ensuring that your type has "
"a larger value for :c:member:`~PyTypeObject.tp_basicsize` than its base type "
"does. Most of the time, this will be true anyway, because either your base "
"type will be :class:`object`, or else you will be adding data members to "
"your base type, and therefore increasing its size."
msgstr ""
msgid "We set the class flags to :c:macro:`Py_TPFLAGS_DEFAULT`. ::"
msgstr ""
msgid ".tp_flags = Py_TPFLAGS_DEFAULT,"
msgstr ""
msgid ""
"All types should include this constant in their flags. It enables all of "
"the members defined until at least Python 3.3. If you need further members, "
"you will need to OR the corresponding flags."
msgstr ""
msgid ""
"We provide a doc string for the type in :c:member:`~PyTypeObject.tp_doc`. ::"
msgstr ""
msgid ".tp_doc = PyDoc_STR(\"Custom objects\"),"
msgstr ""
msgid ""
"To enable object creation, we have to provide "
"a :c:member:`~PyTypeObject.tp_new` handler. This is the equivalent of the "
"Python method :meth:`~object.__new__`, but has to be specified explicitly. "
"In this case, we can just use the default implementation provided by the API "
"function :c:func:`PyType_GenericNew`. ::"
msgstr ""
msgid ".tp_new = PyType_GenericNew,"
msgstr ""
msgid ""
"Everything else in the file should be familiar, except for some code "
"in :c:func:`!custom_module_exec`::"
msgstr ""
msgid ""
"if (PyType_Ready(&CustomType) < 0) {\n"
" return -1;\n"
"}"
msgstr ""
msgid ""
"This initializes the :class:`!Custom` type, filling in a number of members "
"to the appropriate default values, including :c:member:`~PyObject.ob_type` "
"that we initially set to ``NULL``. ::"
msgstr ""
msgid ""
"if (PyModule_AddObjectRef(m, \"Custom\", (PyObject *) &CustomType) < 0) {\n"
" return -1;\n"
"}"
msgstr ""
msgid ""
"This adds the type to the module dictionary. This allows us to "
"create :class:`!Custom` instances by calling the :class:`!Custom` class:"
msgstr ""
msgid ""
">>> import custom\n"
">>> mycustom = custom.Custom()"
msgstr ""
msgid ""
"That's it! All that remains is to build it; put the above code in a file "
"called :file:`custom.c`,"
msgstr ""
msgid ""
"[build-system]\n"
"requires = [\"setuptools\"]\n"
"build-backend = \"setuptools.build_meta\"\n"
"\n"
"[project]\n"
"name = \"custom\"\n"
"version = \"1\"\n"
msgstr ""
msgid "in a file called :file:`pyproject.toml`, and"
msgstr ""
msgid ""
"from setuptools import Extension, setup\n"
"setup(ext_modules=[Extension(\"custom\", [\"custom.c\"])])"
msgstr ""
msgid "in a file called :file:`setup.py`; then typing"
msgstr ""
msgid "$ python -m pip install ."
msgstr ""
msgid ""
"in a shell should produce a file :file:`custom.so` in a subdirectory and "
"install it; now fire up Python --- you should be able to ``import custom`` "
"and play around with ``Custom`` objects."
msgstr ""
msgid "That wasn't so hard, was it?"
msgstr ""
msgid ""
"Of course, the current Custom type is pretty uninteresting. It has no data "
"and doesn't do anything. It can't even be subclassed."
msgstr ""
msgid "Adding data and methods to the Basic example"
msgstr ""
msgid ""
"Let's extend the basic example to add some data and methods. Let's also "
"make the type usable as a base class. We'll create a new module, :mod:`!"
"custom2` that adds these capabilities:"
msgstr ""
msgid ""
"#define PY_SSIZE_T_CLEAN\n"
"#include <Python.h>\n"
"#include <stddef.h> /* for offsetof() */\n"
"\n"
"typedef struct {\n"
" PyObject_HEAD\n"
" PyObject *first; /* first name */\n"
" PyObject *last; /* last name */\n"
" int number;\n"
"} CustomObject;\n"
"\n"
"static void\n"
"Custom_dealloc(PyObject *op)\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" Py_XDECREF(self->first);\n"
" Py_XDECREF(self->last);\n"
" Py_TYPE(self)->tp_free(self);\n"
"}\n"
"\n"
"static PyObject *\n"
"Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)\n"
"{\n"
" CustomObject *self;\n"
" self = (CustomObject *) type->tp_alloc(type, 0);\n"
" if (self != NULL) {\n"
" self->first = Py_GetConstant(Py_CONSTANT_EMPTY_STR);\n"
" if (self->first == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->last = Py_GetConstant(Py_CONSTANT_EMPTY_STR);\n"
" if (self->last == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->number = 0;\n"
" }\n"
" return (PyObject *) self;\n"
"}\n"
"\n"
"static int\n"
"Custom_init(PyObject *op, PyObject *args, PyObject *kwds)\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" static char *kwlist[] = {\"first\", \"last\", \"number\", NULL};\n"
" PyObject *first = NULL, *last = NULL;\n"
"\n"
" if (!PyArg_ParseTupleAndKeywords(args, kwds, \"|OOi\", kwlist,\n"
" &first, &last,\n"
" &self->number))\n"
" return -1;\n"
"\n"
" if (first) {\n"
" Py_XSETREF(self->first, Py_NewRef(first));\n"
" }\n"
" if (last) {\n"
" Py_XSETREF(self->last, Py_NewRef(last));\n"
" }\n"
" return 0;\n"
"}\n"
"\n"
"static PyMemberDef Custom_members[] = {\n"
" {\"first\", Py_T_OBJECT_EX, offsetof(CustomObject, first), 0,\n"
" \"first name\"},\n"
" {\"last\", Py_T_OBJECT_EX, offsetof(CustomObject, last), 0,\n"
" \"last name\"},\n"
" {\"number\", Py_T_INT, offsetof(CustomObject, number), 0,\n"
" \"custom number\"},\n"
" {NULL} /* Sentinel */\n"
"};\n"
"\n"
"static PyObject *\n"
"Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" if (self->first == NULL) {\n"
" PyErr_SetString(PyExc_AttributeError, \"first\");\n"
" return NULL;\n"
" }\n"
" if (self->last == NULL) {\n"
" PyErr_SetString(PyExc_AttributeError, \"last\");\n"
" return NULL;\n"
" }\n"
" return PyUnicode_FromFormat(\"%S %S\", self->first, self->last);\n"
"}\n"
"\n"
"static PyMethodDef Custom_methods[] = {\n"
" {\"name\", Custom_name, METH_NOARGS,\n"
" \"Return the name, combining the first and last name\"\n"
" },\n"
" {NULL} /* Sentinel */\n"
"};\n"
"\n"
"static PyTypeObject CustomType = {\n"
" .ob_base = PyVarObject_HEAD_INIT(NULL, 0)\n"
" .tp_name = \"custom2.Custom\",\n"
" .tp_doc = PyDoc_STR(\"Custom objects\"),\n"
" .tp_basicsize = sizeof(CustomObject),\n"
" .tp_itemsize = 0,\n"
" .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,\n"
" .tp_new = Custom_new,\n"
" .tp_init = Custom_init,\n"
" .tp_dealloc = Custom_dealloc,\n"
" .tp_members = Custom_members,\n"
" .tp_methods = Custom_methods,\n"
"};\n"
"\n"
"static int\n"
"custom_module_exec(PyObject *m)\n"
"{\n"
" if (PyType_Ready(&CustomType) < 0) {\n"
" return -1;\n"
" }\n"
"\n"
" if (PyModule_AddObjectRef(m, \"Custom\", (PyObject *) &CustomType) < 0) "
"{\n"
" return -1;\n"
" }\n"
"\n"
" return 0;\n"
"}\n"
"\n"
"static PyModuleDef_Slot custom_module_slots[] = {\n"
" {Py_mod_exec, custom_module_exec},\n"
" {Py_mod_multiple_interpreters, "
"Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED},\n"
" {0, NULL}\n"
"};\n"
"\n"
"static PyModuleDef custom_module = {\n"
" .m_base = PyModuleDef_HEAD_INIT,\n"
" .m_name = \"custom2\",\n"
" .m_doc = \"Example module that creates an extension type.\",\n"
" .m_size = 0,\n"
" .m_slots = custom_module_slots,\n"
"};\n"
"\n"
"PyMODINIT_FUNC\n"
"PyInit_custom2(void)\n"
"{\n"
" return PyModuleDef_Init(&custom_module);\n"
"}\n"
msgstr ""
msgid "This version of the module has a number of changes."
msgstr ""
msgid ""
"The :class:`!Custom` type now has three data attributes in its C struct, "
"*first*, *last*, and *number*. The *first* and *last* variables are Python "
"strings containing first and last names. The *number* attribute is a C "
"integer."
msgstr ""
msgid "The object structure is updated accordingly::"
msgstr ""
msgid ""
"typedef struct {\n"
" PyObject_HEAD\n"
" PyObject *first; /* first name */\n"
" PyObject *last; /* last name */\n"
" int number;\n"
"} CustomObject;"
msgstr ""
msgid ""
"Because we now have data to manage, we have to be more careful about object "
"allocation and deallocation. At a minimum, we need a deallocation method::"
msgstr ""
msgid ""
"static void\n"
"Custom_dealloc(PyObject *op)\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" Py_XDECREF(self->first);\n"
" Py_XDECREF(self->last);\n"
" Py_TYPE(self)->tp_free(self);\n"
"}"
msgstr ""
msgid "which is assigned to the :c:member:`~PyTypeObject.tp_dealloc` member::"
msgstr ""
msgid ".tp_dealloc = Custom_dealloc,"
msgstr ""
msgid ""
"This method first clears the reference counts of the two Python "
"attributes. :c:func:`Py_XDECREF` correctly handles the case where its "
"argument is ``NULL`` (which might happen here if ``tp_new`` failed midway). "
"It then calls the :c:member:`~PyTypeObject.tp_free` member of the object's "
"type (computed by ``Py_TYPE(self)``) to free the object's memory. Note that "
"the object's type might not be :class:`!CustomType`, because the object may "
"be an instance of a subclass."
msgstr ""
msgid ""
"The explicit cast to ``CustomObject *`` above is needed because we defined "
"``Custom_dealloc`` to take a ``PyObject *`` argument, as the ``tp_dealloc`` "
"function pointer expects to receive a ``PyObject *`` argument. By assigning "
"to the ``tp_dealloc`` slot of a type, we declare that it can only be called "
"with instances of our ``CustomObject`` class, so the cast to ``(CustomObject "
"*)`` is safe. This is object-oriented polymorphism, in C!"
msgstr ""
msgid ""
"In existing code, or in previous versions of this tutorial, you might see "
"similar functions take a pointer to the subtype object structure "
"(``CustomObject*``) directly, like this::"
msgstr ""
msgid ""
"Custom_dealloc(CustomObject *self)\n"
"{\n"
" Py_XDECREF(self->first);\n"
" Py_XDECREF(self->last);\n"
" Py_TYPE(self)->tp_free((PyObject *) self);\n"
"}\n"
"...\n"
".tp_dealloc = (destructor) Custom_dealloc,"
msgstr ""
msgid ""
"This does the same thing on all architectures that CPython supports, but "
"according to the C standard, it invokes undefined behavior."
msgstr ""
msgid ""
"We want to make sure that the first and last names are initialized to empty "
"strings, so we provide a ``tp_new`` implementation::"
msgstr ""
msgid ""
"static PyObject *\n"
"Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)\n"
"{\n"
" CustomObject *self;\n"
" self = (CustomObject *) type->tp_alloc(type, 0);\n"
" if (self != NULL) {\n"
" self->first = PyUnicode_FromString(\"\");\n"
" if (self->first == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->last = PyUnicode_FromString(\"\");\n"
" if (self->last == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->number = 0;\n"
" }\n"
" return (PyObject *) self;\n"
"}"
msgstr ""
msgid "and install it in the :c:member:`~PyTypeObject.tp_new` member::"
msgstr ""
msgid ".tp_new = Custom_new,"
msgstr ""
msgid ""
"The ``tp_new`` handler is responsible for creating (as opposed to "
"initializing) objects of the type. It is exposed in Python as "
"the :meth:`~object.__new__` method. It is not required to define a "
"``tp_new`` member, and indeed many extension types will simply "
"reuse :c:func:`PyType_GenericNew` as done in the first version of "
"the :class:`!Custom` type above. In this case, we use the ``tp_new`` "
"handler to initialize the ``first`` and ``last`` attributes to non-``NULL`` "
"default values."
msgstr ""
msgid ""
"``tp_new`` is passed the type being instantiated (not necessarily "
"``CustomType``, if a subclass is instantiated) and any arguments passed when "
"the type was called, and is expected to return the instance created. "
"``tp_new`` handlers always accept positional and keyword arguments, but they "
"often ignore the arguments, leaving the argument handling to initializer "
"(a.k.a. ``tp_init`` in C or ``__init__`` in Python) methods."
msgstr ""
msgid ""
"``tp_new`` shouldn't call ``tp_init`` explicitly, as the interpreter will do "
"it itself."
msgstr ""
msgid ""
"The ``tp_new`` implementation calls the :c:member:`~PyTypeObject.tp_alloc` "
"slot to allocate memory::"
msgstr ""
msgid "self = (CustomObject *) type->tp_alloc(type, 0);"
msgstr ""
msgid ""
"Since memory allocation may fail, we must check "
"the :c:member:`~PyTypeObject.tp_alloc` result against ``NULL`` before "
"proceeding."
msgstr ""
msgid ""
"We didn't fill the :c:member:`~PyTypeObject.tp_alloc` slot ourselves. "
"Rather :c:func:`PyType_Ready` fills it for us by inheriting it from our base "
"class, which is :class:`object` by default. Most types use the default "
"allocation strategy."
msgstr ""
msgid ""
"If you are creating a co-operative :c:member:`~PyTypeObject.tp_new` (one "
"that calls a base type's :c:member:`~PyTypeObject.tp_new` "
"or :meth:`~object.__new__`), you must *not* try to determine what method to "
"call using method resolution order at runtime. Always statically determine "
"what type you are going to call, and call "
"its :c:member:`~PyTypeObject.tp_new` directly, or via ``type->tp_base-"
">tp_new``. If you do not do this, Python subclasses of your type that also "
"inherit from other Python-defined classes may not work correctly. "
"(Specifically, you may not be able to create instances of such subclasses "
"without getting a :exc:`TypeError`.)"
msgstr ""
msgid ""
"We also define an initialization function which accepts arguments to provide "
"initial values for our instance::"
msgstr ""
msgid ""
"static int\n"
"Custom_init(PyObject *op, PyObject *args, PyObject *kwds)\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" static char *kwlist[] = {\"first\", \"last\", \"number\", NULL};\n"
" PyObject *first = NULL, *last = NULL, *tmp;\n"
"\n"
" if (!PyArg_ParseTupleAndKeywords(args, kwds, \"|OOi\", kwlist,\n"
" &first, &last,\n"
" &self->number))\n"
" return -1;\n"
"\n"
" if (first) {\n"
" tmp = self->first;\n"
" Py_INCREF(first);\n"
" self->first = first;\n"
" Py_XDECREF(tmp);\n"
" }\n"
" if (last) {\n"
" tmp = self->last;\n"
" Py_INCREF(last);\n"
" self->last = last;\n"
" Py_XDECREF(tmp);\n"
" }\n"
" return 0;\n"
"}"
msgstr ""
msgid "by filling the :c:member:`~PyTypeObject.tp_init` slot. ::"
msgstr ""
msgid ".tp_init = Custom_init,"
msgstr ""
msgid ""
"The :c:member:`~PyTypeObject.tp_init` slot is exposed in Python as "
"the :meth:`~object.__init__` method. It is used to initialize an object "
"after it's created. Initializers always accept positional and keyword "
"arguments, and they should return either ``0`` on success or ``-1`` on error."
msgstr ""
msgid ""
"Unlike the ``tp_new`` handler, there is no guarantee that ``tp_init`` is "
"called at all (for example, the :mod:`pickle` module by default doesn't "
"call :meth:`~object.__init__` on unpickled instances). It can also be "
"called multiple times. Anyone can call the :meth:`!__init__` method on our "
"objects. For this reason, we have to be extra careful when assigning the "
"new attribute values. We might be tempted, for example to assign the "
"``first`` member like this::"
msgstr ""
msgid ""
"if (first) {\n"
" Py_XDECREF(self->first);\n"
" Py_INCREF(first);\n"
" self->first = first;\n"
"}"
msgstr ""
msgid ""
"But this would be risky. Our type doesn't restrict the type of the "
"``first`` member, so it could be any kind of object. It could have a "
"destructor that causes code to be executed that tries to access the "
"``first`` member; or that destructor could detach the :term:`thread state "
"<attached thread state>` and let arbitrary code run in other threads that "
"accesses and modifies our object."
msgstr ""
msgid ""
"To be paranoid and protect ourselves against this possibility, we almost "
"always reassign members before decrementing their reference counts. When "
"don't we have to do this?"
msgstr ""
msgid "when we absolutely know that the reference count is greater than 1;"
msgstr ""
msgid ""
"when we know that deallocation of the object [#]_ will neither detach "
"the :term:`thread state <attached thread state>` nor cause any calls back "
"into our type's code;"
msgstr ""
msgid ""
"when decrementing a reference count in "
"a :c:member:`~PyTypeObject.tp_dealloc` handler on a type which doesn't "
"support cyclic garbage collection [#]_."
msgstr ""
msgid ""
"We want to expose our instance variables as attributes. There are a number "
"of ways to do that. The simplest way is to define member definitions::"
msgstr ""
msgid ""
"static PyMemberDef Custom_members[] = {\n"
" {\"first\", Py_T_OBJECT_EX, offsetof(CustomObject, first), 0,\n"
" \"first name\"},\n"
" {\"last\", Py_T_OBJECT_EX, offsetof(CustomObject, last), 0,\n"
" \"last name\"},\n"
" {\"number\", Py_T_INT, offsetof(CustomObject, number), 0,\n"
" \"custom number\"},\n"
" {NULL} /* Sentinel */\n"
"};"
msgstr ""
msgid ""
"and put the definitions in the :c:member:`~PyTypeObject.tp_members` slot::"
msgstr ""
msgid ".tp_members = Custom_members,"
msgstr ""
msgid ""
"Each member definition has a member name, type, offset, access flags and "
"documentation string. See the :ref:`Generic-Attribute-Management` section "
"below for details."
msgstr ""
msgid ""
"A disadvantage of this approach is that it doesn't provide a way to restrict "
"the types of objects that can be assigned to the Python attributes. We "
"expect the first and last names to be strings, but any Python objects can be "
"assigned. Further, the attributes can be deleted, setting the C pointers to "
"``NULL``. Even though we can make sure the members are initialized to non-"
"``NULL`` values, the members can be set to ``NULL`` if the attributes are "
"deleted."
msgstr ""
msgid ""
"We define a single method, :meth:`!Custom.name`, that outputs the objects "
"name as the concatenation of the first and last names. ::"
msgstr ""
msgid ""
"static PyObject *\n"
"Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" if (self->first == NULL) {\n"
" PyErr_SetString(PyExc_AttributeError, \"first\");\n"
" return NULL;\n"
" }\n"
" if (self->last == NULL) {\n"
" PyErr_SetString(PyExc_AttributeError, \"last\");\n"
" return NULL;\n"
" }\n"
" return PyUnicode_FromFormat(\"%S %S\", self->first, self->last);\n"
"}"
msgstr ""
msgid ""
"The method is implemented as a C function that takes a :class:`!Custom` "
"(or :class:`!Custom` subclass) instance as the first argument. Methods "
"always take an instance as the first argument. Methods often take positional "
"and keyword arguments as well, but in this case we don't take any and don't "
"need to accept a positional argument tuple or keyword argument dictionary. "
"This method is equivalent to the Python method:"
msgstr ""
msgid ""
"def name(self):\n"
" return \"%s %s\" % (self.first, self.last)"
msgstr ""
msgid ""
"Note that we have to check for the possibility that our :attr:`!first` "
"and :attr:`!last` members are ``NULL``. This is because they can be "
"deleted, in which case they are set to ``NULL``. It would be better to "
"prevent deletion of these attributes and to restrict the attribute values to "
"be strings. We'll see how to do that in the next section."
msgstr ""
msgid ""
"Now that we've defined the method, we need to create an array of method "
"definitions::"
msgstr ""
msgid ""
"static PyMethodDef Custom_methods[] = {\n"
" {\"name\", Custom_name, METH_NOARGS,\n"
" \"Return the name, combining the first and last name\"\n"
" },\n"
" {NULL} /* Sentinel */\n"
"};"
msgstr ""
msgid ""
"(note that we used the :c:macro:`METH_NOARGS` flag to indicate that the "
"method is expecting no arguments other than *self*)"
msgstr ""
msgid "and assign it to the :c:member:`~PyTypeObject.tp_methods` slot::"
msgstr ""
msgid ".tp_methods = Custom_methods,"
msgstr ""
msgid ""
"Finally, we'll make our type usable as a base class for subclassing. We've "
"written our methods carefully so far so that they don't make any assumptions "
"about the type of the object being created or used, so all we need to do is "
"to add the :c:macro:`Py_TPFLAGS_BASETYPE` to our class flag definition::"
msgstr ""
msgid ".tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,"
msgstr ""
msgid ""
"We rename :c:func:`!PyInit_custom` to :c:func:`!PyInit_custom2`, update the "
"module name in the :c:type:`PyModuleDef` struct, and update the full class "
"name in the :c:type:`PyTypeObject` struct."
msgstr ""
msgid "Finally, we update our :file:`setup.py` file to include the new module,"
msgstr ""
msgid ""
"from setuptools import Extension, setup\n"
"setup(ext_modules=[\n"
" Extension(\"custom\", [\"custom.c\"]),\n"
" Extension(\"custom2\", [\"custom2.c\"]),\n"
"])"
msgstr ""
msgid "and then we re-install so that we can ``import custom2``:"
msgstr ""
msgid "Providing finer control over data attributes"
msgstr ""
msgid ""
"In this section, we'll provide finer control over how the :attr:`!first` "
"and :attr:`!last` attributes are set in the :class:`!Custom` example. In the "
"previous version of our module, the instance variables :attr:`!first` "
"and :attr:`!last` could be set to non-string values or even deleted. We want "
"to make sure that these attributes always contain strings."
msgstr ""
msgid ""
"#define PY_SSIZE_T_CLEAN\n"
"#include <Python.h>\n"
"#include <stddef.h> /* for offsetof() */\n"
"\n"
"typedef struct {\n"
" PyObject_HEAD\n"
" PyObject *first; /* first name */\n"
" PyObject *last; /* last name */\n"
" int number;\n"
"} CustomObject;\n"
"\n"
"static void\n"
"Custom_dealloc(PyObject *op)\n"
"{\n"
" CustomObject *self = (CustomObject *) op;\n"
" Py_XDECREF(self->first);\n"
" Py_XDECREF(self->last);\n"
" Py_TYPE(self)->tp_free(self);\n"
"}\n"
"\n"
"static PyObject *\n"
"Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)\n"
"{\n"
" CustomObject *self;\n"
" self = (CustomObject *) type->tp_alloc(type, 0);\n"
" if (self != NULL) {\n"
" self->first = Py_GetConstant(Py_CONSTANT_EMPTY_STR);\n"
" if (self->first == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->last = Py_GetConstant(Py_CONSTANT_EMPTY_STR);\n"
" if (self->last == NULL) {\n"
" Py_DECREF(self);\n"
" return NULL;\n"
" }\n"
" self->number = 0;\n"
" }\n"
" return (PyObject *) self;\n"
"}\n"
"\n"
"static int\n"
"Custom_init(PyObject *op, PyObject *args, PyObject *kwds)\n"
"{\n"