newtypes_tutorial.po

# Copyright (C) 2001-2018, Python Software Foundation
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#
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#: extending/newtypes_tutorial.rst:7
msgid "Defining Extension Types: Tutorial"
msgstr ""

#: extending/newtypes_tutorial.rst:14
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 ""

#: extending/newtypes_tutorial.rst:24
msgid "The Basics"
msgstr ""

#: extending/newtypes_tutorial.rst:26
msgid ""
"The :term:`CPython` runtime sees all Python objects as variables of type :c:"
"type:`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 ""

#: extending/newtypes_tutorial.rst:35
msgid ""
"So, if you want to define a new extension type, you need to create a new "
"type object."
msgstr ""

#: extending/newtypes_tutorial.rst:38
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 ""

#: extending/newtypes_tutorial.rst:43
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 ""

#: extending/newtypes_tutorial.rst:50
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 ""

#: extending/newtypes_tutorial.rst:53
msgid ""
"What a :class:`Custom` **object** contains: this is the ``CustomObject`` "
"struct, which is allocated once for each :class:`Custom` instance."
msgstr ""

#: extending/newtypes_tutorial.rst:55
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 ""

#: extending/newtypes_tutorial.rst:58
msgid ""
"How to initialize the :mod:`custom` module: this is the ``PyInit_custom`` "
"function and the associated ``custommodule`` struct."
msgstr ""

#: extending/newtypes_tutorial.rst:61
msgid "The first bit is::"
msgstr ""

#: extending/newtypes_tutorial.rst:67
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_REFCNT` "
"and :c:macro:`Py_TYPE` respectively).  The reason for the macro is to "
"abstract away the layout and to enable additional fields in debug builds."
msgstr ""

#: extending/newtypes_tutorial.rst:75
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 ""

#: extending/newtypes_tutorial.rst:78
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 ""

#: extending/newtypes_tutorial.rst:87
msgid "The second bit is the definition of the type object. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:100
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 ""

#: extending/newtypes_tutorial.rst:104
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 ""

#: extending/newtypes_tutorial.rst:109
msgid "We're going to pick it apart, one field at a time::"
msgstr ""

#: extending/newtypes_tutorial.rst:113
msgid ""
"This line is mandatory boilerplate to initialize the ``ob_base`` field "
"mentioned above. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:118
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 ""

#: extending/newtypes_tutorial.rst:128
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 ""

#: extending/newtypes_tutorial.rst:137
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 ""

#: extending/newtypes_tutorial.rst:143
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:`~class.__bases__`, or else it "
"will not be able to call your type's :meth:`__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 ""

#: extending/newtypes_tutorial.rst:153
msgid "We set the class flags to :const:`Py_TPFLAGS_DEFAULT`. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:157
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 ""

#: extending/newtypes_tutorial.rst:161
msgid ""
"We provide a doc string for the type in :c:member:`~PyTypeObject.tp_doc`. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:165
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:"
"`__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 ""

#: extending/newtypes_tutorial.rst:172
msgid ""
"Everything else in the file should be familiar, except for some code in :c:"
"func:`PyInit_custom`::"
msgstr ""

#: extending/newtypes_tutorial.rst:178
msgid ""
"This initializes the :class:`Custom` type, filling in a number of members to "
"the appropriate default values, including :attr:`ob_type` that we initially "
"set to ``NULL``. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:189
msgid ""
"This adds the type to the module dictionary.  This allows us to create :"
"class:`Custom` instances by calling the :class:`Custom` class:"
msgstr ""

#: extending/newtypes_tutorial.rst:197
msgid ""
"That's it!  All that remains is to build it; put the above code in a file "
"called :file:`custom.c` and:"
msgstr ""

#: extending/newtypes_tutorial.rst:206
msgid "in a file called :file:`setup.py`; then typing"
msgstr ""

#: extending/newtypes_tutorial.rst:212
msgid ""
"at a shell should produce a file :file:`custom.so` in a subdirectory; move "
"to that directory and fire up Python --- you should be able to ``import "
"custom`` and play around with Custom objects."
msgstr ""

#: extending/newtypes_tutorial.rst:216
msgid "That wasn't so hard, was it?"
msgstr ""

#: extending/newtypes_tutorial.rst:218
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 ""

#: extending/newtypes_tutorial.rst:222
msgid ""
"While this documentation showcases the standard :mod:`distutils` module for "
"building C extensions, it is recommended in real-world use cases to use the "
"newer and better-maintained ``setuptools`` library.  Documentation on how to "
"do this is out of scope for this document and can be found in the `Python "
"Packaging User's Guide <https://packaging.python.org/tutorials/distributing-"
"packages/>`_."
msgstr ""

#: extending/newtypes_tutorial.rst:230
msgid "Adding data and methods to the Basic example"
msgstr ""

#: extending/newtypes_tutorial.rst:232
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 ""

#: extending/newtypes_tutorial.rst:239
msgid "This version of the module has a number of changes."
msgstr ""

#: extending/newtypes_tutorial.rst:241
msgid "We've added an extra include::"
msgstr ""

#: extending/newtypes_tutorial.rst:245
msgid ""
"This include provides declarations that we use to handle attributes, as "
"described a bit later."
msgstr ""

#: extending/newtypes_tutorial.rst:248
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 ""

#: extending/newtypes_tutorial.rst:252
msgid "The object structure is updated accordingly::"
msgstr ""

#: extending/newtypes_tutorial.rst:261
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 ""

#: extending/newtypes_tutorial.rst:272
msgid "which is assigned to the :c:member:`~PyTypeObject.tp_dealloc` member::"
msgstr ""

#: extending/newtypes_tutorial.rst:276
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 ""

#: extending/newtypes_tutorial.rst:285
msgid ""
"The explicit cast to ``destructor`` above is needed because we defined "
"``Custom_dealloc`` to take a ``CustomObject *`` argument, but the "
"``tp_dealloc`` function pointer expects to receive a ``PyObject *`` "
"argument.  Otherwise, the compiler will emit a warning.  This is object-"
"oriented polymorphism, in C!"
msgstr ""

#: extending/newtypes_tutorial.rst:291
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 ""

#: extending/newtypes_tutorial.rst:315
msgid "and install it in the :c:member:`~PyTypeObject.tp_new` member::"
msgstr ""

#: extending/newtypes_tutorial.rst:319
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:"
"`__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 ``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 ""

#: extending/newtypes_tutorial.rst:327
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 ""

#: extending/newtypes_tutorial.rst:335
msgid ""
"``tp_new`` shouldn't call ``tp_init`` explicitly, as the interpreter will do "
"it itself."
msgstr ""

#: extending/newtypes_tutorial.rst:338
msgid ""
"The ``tp_new`` implementation calls the :c:member:`~PyTypeObject.tp_alloc` "
"slot to allocate memory::"
msgstr ""

#: extending/newtypes_tutorial.rst:343
msgid ""
"Since memory allocation may fail, we must check the :c:member:`~PyTypeObject."
"tp_alloc` result against ``NULL`` before proceeding."
msgstr ""

#: extending/newtypes_tutorial.rst:347
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 ""

#: extending/newtypes_tutorial.rst:353
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:"
"`__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 ""

#: extending/newtypes_tutorial.rst:363
msgid ""
"We also define an initialization function which accepts arguments to provide "
"initial values for our instance::"
msgstr ""

#: extending/newtypes_tutorial.rst:392
msgid "by filling the :c:member:`~PyTypeObject.tp_init` slot. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:396
msgid ""
"The :c:member:`~PyTypeObject.tp_init` slot is exposed in Python as the :meth:"
"`__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 ""

#: extending/newtypes_tutorial.rst:401
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:`__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 ""

#: extending/newtypes_tutorial.rst:415
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 release the :term:`Global "
"interpreter Lock <GIL>` and let arbitrary code run in other threads that "
"accesses and modifies our object."
msgstr ""

#: extending/newtypes_tutorial.rst:422
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 ""

#: extending/newtypes_tutorial.rst:426
msgid "when we absolutely know that the reference count is greater than 1;"
msgstr ""

#: extending/newtypes_tutorial.rst:428
msgid ""
"when we know that deallocation of the object [#]_ will neither release the :"
"term:`GIL` nor cause any calls back into our type's code;"
msgstr ""

#: extending/newtypes_tutorial.rst:431
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 ""

#: extending/newtypes_tutorial.rst:434
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 ""

#: extending/newtypes_tutorial.rst:447
msgid ""
"and put the definitions in the :c:member:`~PyTypeObject.tp_members` slot::"
msgstr ""

#: extending/newtypes_tutorial.rst:451
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 ""

#: extending/newtypes_tutorial.rst:455
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 ""

#: extending/newtypes_tutorial.rst:462
msgid ""
"We define a single method, :meth:`Custom.name()`, that outputs the objects "
"name as the concatenation of the first and last names. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:479
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 ""

#: extending/newtypes_tutorial.rst:491
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 ""

#: extending/newtypes_tutorial.rst:497
msgid ""
"Now that we've defined the method, we need to create an array of method "
"definitions::"
msgstr ""

#: extending/newtypes_tutorial.rst:507
msgid ""
"(note that we used the :const:`METH_NOARGS` flag to indicate that the method "
"is expecting no arguments other than *self*)"
msgstr ""

#: extending/newtypes_tutorial.rst:510
msgid "and assign it to the :c:member:`~PyTypeObject.tp_methods` slot::"
msgstr ""

#: extending/newtypes_tutorial.rst:514
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 :const:`Py_TPFLAGS_BASETYPE` to our class flag definition::"
msgstr ""

#: extending/newtypes_tutorial.rst:521
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 ""

#: extending/newtypes_tutorial.rst:525
msgid "Finally, we update our :file:`setup.py` file to build the new module:"
msgstr ""

#: extending/newtypes_tutorial.rst:538
msgid "Providing finer control over data attributes"
msgstr ""

#: extending/newtypes_tutorial.rst:540
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 ""

#: extending/newtypes_tutorial.rst:549
msgid ""
"To provide greater control, over the :attr:`first` and :attr:`last` "
"attributes, we'll use custom getter and setter functions.  Here are the "
"functions for getting and setting the :attr:`first` attribute::"
msgstr ""

#: extending/newtypes_tutorial.rst:580
msgid ""
"The getter function is passed a :class:`Custom` object and a \"closure\", "
"which is a void pointer.  In this case, the closure is ignored.  (The "
"closure supports an advanced usage in which definition data is passed to the "
"getter and setter. This could, for example, be used to allow a single set of "
"getter and setter functions that decide the attribute to get or set based on "
"data in the closure.)"
msgstr ""

#: extending/newtypes_tutorial.rst:586
msgid ""
"The setter function is passed the :class:`Custom` object, the new value, and "
"the closure.  The new value may be ``NULL``, in which case the attribute is "
"being deleted.  In our setter, we raise an error if the attribute is deleted "
"or if its new value is not a string."
msgstr ""

#: extending/newtypes_tutorial.rst:591
msgid "We create an array of :c:type:`PyGetSetDef` structures::"
msgstr ""

#: extending/newtypes_tutorial.rst:601
msgid "and register it in the :c:member:`~PyTypeObject.tp_getset` slot::"
msgstr ""

#: extending/newtypes_tutorial.rst:605
msgid ""
"The last item in a :c:type:`PyGetSetDef` structure is the \"closure\" "
"mentioned above.  In this case, we aren't using a closure, so we just pass "
"``NULL``."
msgstr ""

#: extending/newtypes_tutorial.rst:608
msgid "We also remove the member definitions for these attributes::"
msgstr ""

#: extending/newtypes_tutorial.rst:616
msgid ""
"We also need to update the :c:member:`~PyTypeObject.tp_init` handler to only "
"allow strings [#]_ to be passed::"
msgstr ""

#: extending/newtypes_tutorial.rst:645
msgid ""
"With these changes, we can assure that the ``first`` and ``last`` members "
"are never ``NULL`` so we can remove checks for ``NULL`` values in almost all "
"cases. This means that most of the :c:func:`Py_XDECREF` calls can be "
"converted to :c:func:`Py_DECREF` calls.  The only place we can't change "
"these calls is in the ``tp_dealloc`` implementation, where there is the "
"possibility that the initialization of these members failed in ``tp_new``."
msgstr ""

#: extending/newtypes_tutorial.rst:652
msgid ""
"We also rename the module initialization function and module name in the "
"initialization function, as we did before, and we add an extra definition to "
"the :file:`setup.py` file."
msgstr ""

#: extending/newtypes_tutorial.rst:658
msgid "Supporting cyclic garbage collection"
msgstr ""

#: extending/newtypes_tutorial.rst:660
msgid ""
"Python has a :term:`cyclic garbage collector (GC) <garbage collection>` that "
"can identify unneeded objects even when their reference counts are not zero. "
"This can happen when objects are involved in cycles.  For example, consider:"
msgstr ""

#: extending/newtypes_tutorial.rst:670
msgid ""
"In this example, we create a list that contains itself. When we delete it, "
"it still has a reference from itself. Its reference count doesn't drop to "
"zero. Fortunately, Python's cyclic garbage collector will eventually figure "
"out that the list is garbage and free it."
msgstr ""

#: extending/newtypes_tutorial.rst:675
msgid ""
"In the second version of the :class:`Custom` example, we allowed any kind of "
"object to be stored in the :attr:`first` or :attr:`last` attributes [#]_. "
"Besides, in the second and third versions, we allowed subclassing :class:"
"`Custom`, and subclasses may add arbitrary attributes.  For any of those two "
"reasons, :class:`Custom` objects can participate in cycles:"
msgstr ""

#: extending/newtypes_tutorial.rst:689
msgid ""
"To allow a :class:`Custom` instance participating in a reference cycle to be "
"properly detected and collected by the cyclic GC, our :class:`Custom` type "
"needs to fill two additional slots and to enable a flag that enables these "
"slots:"
msgstr ""

#: extending/newtypes_tutorial.rst:696
msgid ""
"First, the traversal method lets the cyclic GC know about subobjects that "
"could participate in cycles::"
msgstr ""

#: extending/newtypes_tutorial.rst:716
msgid ""
"For each subobject that can participate in cycles, we need to call the :c:"
"func:`visit` function, which is passed to the traversal method. The :c:func:"
"`visit` function takes as arguments the subobject and the extra argument "
"*arg* passed to the traversal method.  It returns an integer value that must "
"be returned if it is non-zero."
msgstr ""

#: extending/newtypes_tutorial.rst:722
msgid ""
"Python provides a :c:func:`Py_VISIT` macro that automates calling visit "
"functions.  With :c:func:`Py_VISIT`, we can minimize the amount of "
"boilerplate in ``Custom_traverse``::"
msgstr ""

#: extending/newtypes_tutorial.rst:735
msgid ""
"The :c:member:`~PyTypeObject.tp_traverse` implementation must name its "
"arguments exactly *visit* and *arg* in order to use :c:func:`Py_VISIT`."
msgstr ""

#: extending/newtypes_tutorial.rst:738
msgid ""
"Second, we need to provide a method for clearing any subobjects that can "
"participate in cycles::"
msgstr ""

#: extending/newtypes_tutorial.rst:749
msgid ""
"Notice the use of the :c:func:`Py_CLEAR` macro.  It is the recommended and "
"safe way to clear data attributes of arbitrary types while decrementing "
"their reference counts.  If you were to call :c:func:`Py_XDECREF` instead on "
"the attribute before setting it to ``NULL``, there is a possibility that the "
"attribute's destructor would call back into code that reads the attribute "
"again (*especially* if there is a reference cycle)."
msgstr ""

#: extending/newtypes_tutorial.rst:757
msgid "You could emulate :c:func:`Py_CLEAR` by writing::"
msgstr ""

#: extending/newtypes_tutorial.rst:764
msgid ""
"Nevertheless, it is much easier and less error-prone to always use :c:func:"
"`Py_CLEAR` when deleting an attribute.  Don't try to micro-optimize at the "
"expense of robustness!"
msgstr ""

#: extending/newtypes_tutorial.rst:768
msgid ""
"The deallocator ``Custom_dealloc`` may call arbitrary code when clearing "
"attributes.  It means the circular GC can be triggered inside the function. "
"Since the GC assumes reference count is not zero, we need to untrack the "
"object from the GC by calling :c:func:`PyObject_GC_UnTrack` before clearing "
"members. Here is our reimplemented deallocator using :c:func:"
"`PyObject_GC_UnTrack` and ``Custom_clear``::"
msgstr ""

#: extending/newtypes_tutorial.rst:783
msgid ""
"Finally, we add the :const:`Py_TPFLAGS_HAVE_GC` flag to the class flags::"
msgstr ""

#: extending/newtypes_tutorial.rst:787
msgid ""
"That's pretty much it.  If we had written custom :c:member:`~PyTypeObject."
"tp_alloc` or :c:member:`~PyTypeObject.tp_free` handlers, we'd need to modify "
"them for cyclic garbage collection.  Most extensions will use the versions "
"automatically provided."
msgstr ""

#: extending/newtypes_tutorial.rst:793
msgid "Subclassing other types"
msgstr ""

#: extending/newtypes_tutorial.rst:795
msgid ""
"It is possible to create new extension types that are derived from existing "
"types. It is easiest to inherit from the built in types, since an extension "
"can easily use the :c:type:`PyTypeObject` it needs. It can be difficult to "
"share these :c:type:`PyTypeObject` structures between extension modules."
msgstr ""

#: extending/newtypes_tutorial.rst:800
msgid ""
"In this example we will create a :class:`SubList` type that inherits from "
"the built-in :class:`list` type. The new type will be completely compatible "
"with regular lists, but will have an additional :meth:`increment` method "
"that increases an internal counter:"
msgstr ""

#: extending/newtypes_tutorial.rst:820
msgid ""
"As you can see, the source code closely resembles the :class:`Custom` "
"examples in previous sections. We will break down the main differences "
"between them. ::"
msgstr ""

#: extending/newtypes_tutorial.rst:828
msgid ""
"The primary difference for derived type objects is that the base type's "
"object structure must be the first value.  The base type will already "
"include the :c:func:`PyObject_HEAD` at the beginning of its structure."
msgstr ""

#: extending/newtypes_tutorial.rst:832
msgid ""
"When a Python object is a :class:`SubList` instance, its ``PyObject *`` "
"pointer can be safely cast to both ``PyListObject *`` and ``SubListObject "
"*``::"
msgstr ""

#: extending/newtypes_tutorial.rst:844
msgid ""
"We see above how to call through to the :attr:`__init__` method of the base "
"type."
msgstr ""

#: extending/newtypes_tutorial.rst:847
msgid ""
"This pattern is important when writing a type with custom :c:member:"
"`~PyTypeObject.tp_new` and :c:member:`~PyTypeObject.tp_dealloc` members.  "
"The :c:member:`~PyTypeObject.tp_new` handler should not actually create the "
"memory for the object with its :c:member:`~PyTypeObject.tp_alloc`, but let "
"the base class handle it by calling its own :c:member:`~PyTypeObject.tp_new`."
msgstr ""

#: extending/newtypes_tutorial.rst:853
msgid ""
"The :c:type:`PyTypeObject` struct supports a :c:member:`~PyTypeObject."
"tp_base` specifying the type's concrete base class.  Due to cross-platform "
"compiler issues, you can't fill that field directly with a reference to :c:"
"type:`PyList_Type`; it should be done later in the module initialization "
"function::"
msgstr ""

#: extending/newtypes_tutorial.rst:881
msgid ""
"Before calling :c:func:`PyType_Ready`, the type structure must have the :c:"
"member:`~PyTypeObject.tp_base` slot filled in.  When we are deriving an "
"existing type, it is not necessary to fill out the :c:member:`~PyTypeObject."
"tp_alloc` slot with :c:func:`PyType_GenericNew` -- the allocation function "
"from the base type will be inherited."
msgstr ""

#: extending/newtypes_tutorial.rst:887
msgid ""
"After that, calling :c:func:`PyType_Ready` and adding the type object to the "
"module is the same as with the basic :class:`Custom` examples."
msgstr ""

#: extending/newtypes_tutorial.rst:892
msgid "Footnotes"
msgstr "Notes"

#: extending/newtypes_tutorial.rst:893
msgid ""
"This is true when we know that the object is a basic type, like a string or "
"a float."
msgstr ""

#: extending/newtypes_tutorial.rst:896
msgid ""
"We relied on this in the :c:member:`~PyTypeObject.tp_dealloc` handler in "
"this example, because our type doesn't support garbage collection."
msgstr ""

#: extending/newtypes_tutorial.rst:899
msgid ""
"We now know that the first and last members are strings, so perhaps we could "
"be less careful about decrementing their reference counts, however, we "
"accept instances of string subclasses.  Even though deallocating normal "
"strings won't call back into our objects, we can't guarantee that "
"deallocating an instance of a string subclass won't call back into our "
"objects."
msgstr ""

#: extending/newtypes_tutorial.rst:905
msgid ""
"Also, even with our attributes restricted to strings instances, the user "
"could pass arbitrary :class:`str` subclasses and therefore still create "
"reference cycles."
msgstr ""