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1314 lines (1152 loc) · 54.9 KB
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# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001-202DESCRIPTIVE TITLE., Python Software Foundation
# This file is distributed under the same license as the Python package.
#
# Translators:
# Leon H., 2017
msgid ""
msgstr ""
"Project-Id-Version: Python 3.12\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2023-08-18 00:03+0000\n"
"PO-Revision-Date: 2018-05-23 14:34+0000\n"
"Last-Translator: Adrian Liaw <adrianliaw2000@gmail.com>\n"
"Language-Team: Chinese - TAIWAN (https://github.com/python/python-docs-zh-"
"tw)\n"
"Language: zh_TW\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=1; plural=0;\n"
#: ../../extending/extending.rst:8
msgid "Extending Python with C or C++"
msgstr "以 C 或 C++ 擴充 Python"
#: ../../extending/extending.rst:10
msgid ""
"It is quite easy to add new built-in modules to Python, if you know how to "
"program in C. Such :dfn:`extension modules` can do two things that can't be "
"done directly in Python: they can implement new built-in object types, and "
"they can call C library functions and system calls."
msgstr ""
#: ../../extending/extending.rst:15
msgid ""
"To support extensions, the Python API (Application Programmers Interface) "
"defines a set of functions, macros and variables that provide access to most "
"aspects of the Python run-time system. The Python API is incorporated in a "
"C source file by including the header ``\"Python.h\"``."
msgstr ""
#: ../../extending/extending.rst:20
msgid ""
"The compilation of an extension module depends on its intended use as well "
"as on your system setup; details are given in later chapters."
msgstr ""
#: ../../extending/extending.rst:25
msgid ""
"The C extension interface is specific to CPython, and extension modules do "
"not work on other Python implementations. In many cases, it is possible to "
"avoid writing C extensions and preserve portability to other "
"implementations. For example, if your use case is calling C library "
"functions or system calls, you should consider using the :mod:`ctypes` "
"module or the `cffi <https://cffi.readthedocs.io/>`_ library rather than "
"writing custom C code. These modules let you write Python code to interface "
"with C code and are more portable between implementations of Python than "
"writing and compiling a C extension module."
msgstr ""
#: ../../extending/extending.rst:40
msgid "A Simple Example"
msgstr "一個簡單範例"
#: ../../extending/extending.rst:42
msgid ""
"Let's create an extension module called ``spam`` (the favorite food of Monty "
"Python fans...) and let's say we want to create a Python interface to the C "
"library function :c:func:`system` [#]_. This function takes a null-"
"terminated character string as argument and returns an integer. We want "
"this function to be callable from Python as follows:"
msgstr ""
#: ../../extending/extending.rst:53
msgid ""
"Begin by creating a file :file:`spammodule.c`. (Historically, if a module "
"is called ``spam``, the C file containing its implementation is called :file:"
"`spammodule.c`; if the module name is very long, like ``spammify``, the "
"module name can be just :file:`spammify.c`.)"
msgstr ""
#: ../../extending/extending.rst:58
msgid "The first two lines of our file can be::"
msgstr ""
#: ../../extending/extending.rst:63
msgid ""
"which pulls in the Python API (you can add a comment describing the purpose "
"of the module and a copyright notice if you like)."
msgstr ""
#: ../../extending/extending.rst:68
msgid ""
"Since Python may define some pre-processor definitions which affect the "
"standard headers on some systems, you *must* include :file:`Python.h` before "
"any standard headers are included."
msgstr ""
#: ../../extending/extending.rst:72
msgid ""
"It is recommended to always define ``PY_SSIZE_T_CLEAN`` before including "
"``Python.h``. See :ref:`parsetuple` for a description of this macro."
msgstr ""
#: ../../extending/extending.rst:75
msgid ""
"All user-visible symbols defined by :file:`Python.h` have a prefix of ``Py`` "
"or ``PY``, except those defined in standard header files. For convenience, "
"and since they are used extensively by the Python interpreter, ``\"Python."
"h\"`` includes a few standard header files: ``<stdio.h>``, ``<string.h>``, "
"``<errno.h>``, and ``<stdlib.h>``. If the latter header file does not exist "
"on your system, it declares the functions :c:func:`malloc`, :c:func:`free` "
"and :c:func:`realloc` directly."
msgstr ""
#: ../../extending/extending.rst:83
msgid ""
"The next thing we add to our module file is the C function that will be "
"called when the Python expression ``spam.system(string)`` is evaluated "
"(we'll see shortly how it ends up being called)::"
msgstr ""
#: ../../extending/extending.rst:99
msgid ""
"There is a straightforward translation from the argument list in Python (for "
"example, the single expression ``\"ls -l\"``) to the arguments passed to the "
"C function. The C function always has two arguments, conventionally named "
"*self* and *args*."
msgstr ""
#: ../../extending/extending.rst:104
msgid ""
"The *self* argument points to the module object for module-level functions; "
"for a method it would point to the object instance."
msgstr ""
#: ../../extending/extending.rst:107
msgid ""
"The *args* argument will be a pointer to a Python tuple object containing "
"the arguments. Each item of the tuple corresponds to an argument in the "
"call's argument list. The arguments are Python objects --- in order to do "
"anything with them in our C function we have to convert them to C values. "
"The function :c:func:`PyArg_ParseTuple` in the Python API checks the "
"argument types and converts them to C values. It uses a template string to "
"determine the required types of the arguments as well as the types of the C "
"variables into which to store the converted values. More about this later."
msgstr ""
#: ../../extending/extending.rst:116
msgid ""
":c:func:`PyArg_ParseTuple` returns true (nonzero) if all arguments have the "
"right type and its components have been stored in the variables whose "
"addresses are passed. It returns false (zero) if an invalid argument list "
"was passed. In the latter case it also raises an appropriate exception so "
"the calling function can return ``NULL`` immediately (as we saw in the "
"example)."
msgstr ""
#: ../../extending/extending.rst:126
msgid "Intermezzo: Errors and Exceptions"
msgstr ""
#: ../../extending/extending.rst:128
msgid ""
"An important convention throughout the Python interpreter is the following: "
"when a function fails, it should set an exception condition and return an "
"error value (usually ``-1`` or a ``NULL`` pointer). Exception information "
"is stored in three members of the interpreter's thread state. These are "
"``NULL`` if there is no exception. Otherwise they are the C equivalents of "
"the members of the Python tuple returned by :meth:`sys.exc_info`. These are "
"the exception type, exception instance, and a traceback object. It is "
"important to know about them to understand how errors are passed around."
msgstr ""
#: ../../extending/extending.rst:137
msgid ""
"The Python API defines a number of functions to set various types of "
"exceptions."
msgstr ""
#: ../../extending/extending.rst:139
msgid ""
"The most common one is :c:func:`PyErr_SetString`. Its arguments are an "
"exception object and a C string. The exception object is usually a "
"predefined object like :c:data:`PyExc_ZeroDivisionError`. The C string "
"indicates the cause of the error and is converted to a Python string object "
"and stored as the \"associated value\" of the exception."
msgstr ""
#: ../../extending/extending.rst:145
msgid ""
"Another useful function is :c:func:`PyErr_SetFromErrno`, which only takes an "
"exception argument and constructs the associated value by inspection of the "
"global variable :c:data:`errno`. The most general function is :c:func:"
"`PyErr_SetObject`, which takes two object arguments, the exception and its "
"associated value. You don't need to :c:func:`Py_INCREF` the objects passed "
"to any of these functions."
msgstr ""
#: ../../extending/extending.rst:152
msgid ""
"You can test non-destructively whether an exception has been set with :c:"
"func:`PyErr_Occurred`. This returns the current exception object, or "
"``NULL`` if no exception has occurred. You normally don't need to call :c:"
"func:`PyErr_Occurred` to see whether an error occurred in a function call, "
"since you should be able to tell from the return value."
msgstr ""
#: ../../extending/extending.rst:158
msgid ""
"When a function *f* that calls another function *g* detects that the latter "
"fails, *f* should itself return an error value (usually ``NULL`` or "
"``-1``). It should *not* call one of the ``PyErr_*`` functions --- one has "
"already been called by *g*. *f*'s caller is then supposed to also return an "
"error indication to *its* caller, again *without* calling ``PyErr_*``, and "
"so on --- the most detailed cause of the error was already reported by the "
"function that first detected it. Once the error reaches the Python "
"interpreter's main loop, this aborts the currently executing Python code and "
"tries to find an exception handler specified by the Python programmer."
msgstr ""
#: ../../extending/extending.rst:168
msgid ""
"(There are situations where a module can actually give a more detailed error "
"message by calling another ``PyErr_*`` function, and in such cases it is "
"fine to do so. As a general rule, however, this is not necessary, and can "
"cause information about the cause of the error to be lost: most operations "
"can fail for a variety of reasons.)"
msgstr ""
#: ../../extending/extending.rst:174
msgid ""
"To ignore an exception set by a function call that failed, the exception "
"condition must be cleared explicitly by calling :c:func:`PyErr_Clear`. The "
"only time C code should call :c:func:`PyErr_Clear` is if it doesn't want to "
"pass the error on to the interpreter but wants to handle it completely by "
"itself (possibly by trying something else, or pretending nothing went wrong)."
msgstr ""
#: ../../extending/extending.rst:180
msgid ""
"Every failing :c:func:`malloc` call must be turned into an exception --- the "
"direct caller of :c:func:`malloc` (or :c:func:`realloc`) must call :c:func:"
"`PyErr_NoMemory` and return a failure indicator itself. All the object-"
"creating functions (for example, :c:func:`PyLong_FromLong`) already do this, "
"so this note is only relevant to those who call :c:func:`malloc` directly."
msgstr ""
#: ../../extending/extending.rst:186
msgid ""
"Also note that, with the important exception of :c:func:`PyArg_ParseTuple` "
"and friends, functions that return an integer status usually return a "
"positive value or zero for success and ``-1`` for failure, like Unix system "
"calls."
msgstr ""
#: ../../extending/extending.rst:190
msgid ""
"Finally, be careful to clean up garbage (by making :c:func:`Py_XDECREF` or :"
"c:func:`Py_DECREF` calls for objects you have already created) when you "
"return an error indicator!"
msgstr ""
#: ../../extending/extending.rst:194
msgid ""
"The choice of which exception to raise is entirely yours. There are "
"predeclared C objects corresponding to all built-in Python exceptions, such "
"as :c:data:`PyExc_ZeroDivisionError`, which you can use directly. Of course, "
"you should choose exceptions wisely --- don't use :c:data:`PyExc_TypeError` "
"to mean that a file couldn't be opened (that should probably be :c:data:"
"`PyExc_OSError`). If something's wrong with the argument list, the :c:func:"
"`PyArg_ParseTuple` function usually raises :c:data:`PyExc_TypeError`. If "
"you have an argument whose value must be in a particular range or must "
"satisfy other conditions, :c:data:`PyExc_ValueError` is appropriate."
msgstr ""
#: ../../extending/extending.rst:204
msgid ""
"You can also define a new exception that is unique to your module. For this, "
"you usually declare a static object variable at the beginning of your file::"
msgstr ""
#: ../../extending/extending.rst:209
msgid ""
"and initialize it in your module's initialization function (:c:func:`!"
"PyInit_spam`) with an exception object::"
msgstr ""
#: ../../extending/extending.rst:233
msgid ""
"Note that the Python name for the exception object is :exc:`!spam.error`. "
"The :c:func:`PyErr_NewException` function may create a class with the base "
"class being :exc:`Exception` (unless another class is passed in instead of "
"``NULL``), described in :ref:`bltin-exceptions`."
msgstr ""
#: ../../extending/extending.rst:238
msgid ""
"Note also that the :c:data:`!SpamError` variable retains a reference to the "
"newly created exception class; this is intentional! Since the exception "
"could be removed from the module by external code, an owned reference to the "
"class is needed to ensure that it will not be discarded, causing :c:data:`!"
"SpamError` to become a dangling pointer. Should it become a dangling "
"pointer, C code which raises the exception could cause a core dump or other "
"unintended side effects."
msgstr ""
#: ../../extending/extending.rst:245
msgid ""
"We discuss the use of :c:macro:`PyMODINIT_FUNC` as a function return type "
"later in this sample."
msgstr ""
#: ../../extending/extending.rst:248
msgid ""
"The :exc:`!spam.error` exception can be raised in your extension module "
"using a call to :c:func:`PyErr_SetString` as shown below::"
msgstr ""
#: ../../extending/extending.rst:271
msgid "Back to the Example"
msgstr "回到範例"
#: ../../extending/extending.rst:273
msgid ""
"Going back to our example function, you should now be able to understand "
"this statement::"
msgstr ""
#: ../../extending/extending.rst:279
msgid ""
"It returns ``NULL`` (the error indicator for functions returning object "
"pointers) if an error is detected in the argument list, relying on the "
"exception set by :c:func:`PyArg_ParseTuple`. Otherwise the string value of "
"the argument has been copied to the local variable :c:data:`!command`. This "
"is a pointer assignment and you are not supposed to modify the string to "
"which it points (so in Standard C, the variable :c:data:`!command` should "
"properly be declared as ``const char *command``)."
msgstr ""
#: ../../extending/extending.rst:287
msgid ""
"The next statement is a call to the Unix function :c:func:`system`, passing "
"it the string we just got from :c:func:`PyArg_ParseTuple`::"
msgstr ""
#: ../../extending/extending.rst:292
msgid ""
"Our :func:`!spam.system` function must return the value of :c:data:`!sts` as "
"a Python object. This is done using the function :c:func:"
"`PyLong_FromLong`. ::"
msgstr ""
#: ../../extending/extending.rst:297
msgid ""
"In this case, it will return an integer object. (Yes, even integers are "
"objects on the heap in Python!)"
msgstr ""
#: ../../extending/extending.rst:300
msgid ""
"If you have a C function that returns no useful argument (a function "
"returning :c:expr:`void`), the corresponding Python function must return "
"``None``. You need this idiom to do so (which is implemented by the :c:"
"macro:`Py_RETURN_NONE` macro)::"
msgstr ""
#: ../../extending/extending.rst:308
msgid ""
":c:data:`Py_None` is the C name for the special Python object ``None``. It "
"is a genuine Python object rather than a ``NULL`` pointer, which means "
"\"error\" in most contexts, as we have seen."
msgstr ""
#: ../../extending/extending.rst:316
msgid "The Module's Method Table and Initialization Function"
msgstr ""
#: ../../extending/extending.rst:318
msgid ""
"I promised to show how :c:func:`!spam_system` is called from Python "
"programs. First, we need to list its name and address in a \"method table\"::"
msgstr ""
#: ../../extending/extending.rst:329
msgid ""
"Note the third entry (``METH_VARARGS``). This is a flag telling the "
"interpreter the calling convention to be used for the C function. It should "
"normally always be ``METH_VARARGS`` or ``METH_VARARGS | METH_KEYWORDS``; a "
"value of ``0`` means that an obsolete variant of :c:func:`PyArg_ParseTuple` "
"is used."
msgstr ""
#: ../../extending/extending.rst:334
msgid ""
"When using only ``METH_VARARGS``, the function should expect the Python-"
"level parameters to be passed in as a tuple acceptable for parsing via :c:"
"func:`PyArg_ParseTuple`; more information on this function is provided below."
msgstr ""
#: ../../extending/extending.rst:338
msgid ""
"The :c:macro:`METH_KEYWORDS` bit may be set in the third field if keyword "
"arguments should be passed to the function. In this case, the C function "
"should accept a third ``PyObject *`` parameter which will be a dictionary of "
"keywords. Use :c:func:`PyArg_ParseTupleAndKeywords` to parse the arguments "
"to such a function."
msgstr ""
#: ../../extending/extending.rst:344
msgid ""
"The method table must be referenced in the module definition structure::"
msgstr ""
#: ../../extending/extending.rst:355
msgid ""
"This structure, in turn, must be passed to the interpreter in the module's "
"initialization function. The initialization function must be named :c:func:"
"`!PyInit_name`, where *name* is the name of the module, and should be the "
"only non-\\ ``static`` item defined in the module file::"
msgstr ""
#: ../../extending/extending.rst:366
msgid ""
"Note that :c:macro:`PyMODINIT_FUNC` declares the function as ``PyObject *`` "
"return type, declares any special linkage declarations required by the "
"platform, and for C++ declares the function as ``extern \"C\"``."
msgstr ""
#: ../../extending/extending.rst:370
msgid ""
"When the Python program imports module :mod:`!spam` for the first time, :c:"
"func:`!PyInit_spam` is called. (See below for comments about embedding "
"Python.) It calls :c:func:`PyModule_Create`, which returns a module object, "
"and inserts built-in function objects into the newly created module based "
"upon the table (an array of :c:type:`PyMethodDef` structures) found in the "
"module definition. :c:func:`PyModule_Create` returns a pointer to the module "
"object that it creates. It may abort with a fatal error for certain errors, "
"or return ``NULL`` if the module could not be initialized satisfactorily. "
"The init function must return the module object to its caller, so that it "
"then gets inserted into ``sys.modules``."
msgstr ""
#: ../../extending/extending.rst:381
msgid ""
"When embedding Python, the :c:func:`!PyInit_spam` function is not called "
"automatically unless there's an entry in the :c:data:`PyImport_Inittab` "
"table. To add the module to the initialization table, use :c:func:"
"`PyImport_AppendInittab`, optionally followed by an import of the module::"
msgstr ""
#: ../../extending/extending.rst:425
msgid ""
"Removing entries from ``sys.modules`` or importing compiled modules into "
"multiple interpreters within a process (or following a :c:func:`fork` "
"without an intervening :c:func:`exec`) can create problems for some "
"extension modules. Extension module authors should exercise caution when "
"initializing internal data structures."
msgstr ""
#: ../../extending/extending.rst:431
msgid ""
"A more substantial example module is included in the Python source "
"distribution as :file:`Modules/xxmodule.c`. This file may be used as a "
"template or simply read as an example."
msgstr ""
#: ../../extending/extending.rst:437
msgid ""
"Unlike our ``spam`` example, ``xxmodule`` uses *multi-phase initialization* "
"(new in Python 3.5), where a PyModuleDef structure is returned from "
"``PyInit_spam``, and creation of the module is left to the import machinery. "
"For details on multi-phase initialization, see :PEP:`489`."
msgstr ""
#: ../../extending/extending.rst:446
msgid "Compilation and Linkage"
msgstr ""
#: ../../extending/extending.rst:448
msgid ""
"There are two more things to do before you can use your new extension: "
"compiling and linking it with the Python system. If you use dynamic "
"loading, the details may depend on the style of dynamic loading your system "
"uses; see the chapters about building extension modules (chapter :ref:"
"`building`) and additional information that pertains only to building on "
"Windows (chapter :ref:`building-on-windows`) for more information about this."
msgstr ""
#: ../../extending/extending.rst:455
msgid ""
"If you can't use dynamic loading, or if you want to make your module a "
"permanent part of the Python interpreter, you will have to change the "
"configuration setup and rebuild the interpreter. Luckily, this is very "
"simple on Unix: just place your file (:file:`spammodule.c` for example) in "
"the :file:`Modules/` directory of an unpacked source distribution, add a "
"line to the file :file:`Modules/Setup.local` describing your file:"
msgstr ""
#: ../../extending/extending.rst:466
msgid ""
"and rebuild the interpreter by running :program:`make` in the toplevel "
"directory. You can also run :program:`make` in the :file:`Modules/` "
"subdirectory, but then you must first rebuild :file:`Makefile` there by "
"running ':program:`make` Makefile'. (This is necessary each time you change "
"the :file:`Setup` file.)"
msgstr ""
#: ../../extending/extending.rst:472
msgid ""
"If your module requires additional libraries to link with, these can be "
"listed on the line in the configuration file as well, for instance:"
msgstr ""
#: ../../extending/extending.rst:483
msgid "Calling Python Functions from C"
msgstr ""
#: ../../extending/extending.rst:485
msgid ""
"So far we have concentrated on making C functions callable from Python. The "
"reverse is also useful: calling Python functions from C. This is especially "
"the case for libraries that support so-called \"callback\" functions. If a "
"C interface makes use of callbacks, the equivalent Python often needs to "
"provide a callback mechanism to the Python programmer; the implementation "
"will require calling the Python callback functions from a C callback. Other "
"uses are also imaginable."
msgstr ""
#: ../../extending/extending.rst:493
msgid ""
"Fortunately, the Python interpreter is easily called recursively, and there "
"is a standard interface to call a Python function. (I won't dwell on how to "
"call the Python parser with a particular string as input --- if you're "
"interested, have a look at the implementation of the :option:`-c` command "
"line option in :file:`Modules/main.c` from the Python source code.)"
msgstr ""
#: ../../extending/extending.rst:499
msgid ""
"Calling a Python function is easy. First, the Python program must somehow "
"pass you the Python function object. You should provide a function (or some "
"other interface) to do this. When this function is called, save a pointer "
"to the Python function object (be careful to :c:func:`Py_INCREF` it!) in a "
"global variable --- or wherever you see fit. For example, the following "
"function might be part of a module definition::"
msgstr ""
#: ../../extending/extending.rst:529
msgid ""
"This function must be registered with the interpreter using the :c:macro:"
"`METH_VARARGS` flag; this is described in section :ref:`methodtable`. The :"
"c:func:`PyArg_ParseTuple` function and its arguments are documented in "
"section :ref:`parsetuple`."
msgstr ""
#: ../../extending/extending.rst:534
msgid ""
"The macros :c:func:`Py_XINCREF` and :c:func:`Py_XDECREF` increment/decrement "
"the reference count of an object and are safe in the presence of ``NULL`` "
"pointers (but note that *temp* will not be ``NULL`` in this context). More "
"info on them in section :ref:`refcounts`."
msgstr ""
#: ../../extending/extending.rst:541
msgid ""
"Later, when it is time to call the function, you call the C function :c:func:"
"`PyObject_CallObject`. This function has two arguments, both pointers to "
"arbitrary Python objects: the Python function, and the argument list. The "
"argument list must always be a tuple object, whose length is the number of "
"arguments. To call the Python function with no arguments, pass in ``NULL``, "
"or an empty tuple; to call it with one argument, pass a singleton tuple. :c:"
"func:`Py_BuildValue` returns a tuple when its format string consists of zero "
"or more format codes between parentheses. For example::"
msgstr ""
#: ../../extending/extending.rst:561
msgid ""
":c:func:`PyObject_CallObject` returns a Python object pointer: this is the "
"return value of the Python function. :c:func:`PyObject_CallObject` is "
"\"reference-count-neutral\" with respect to its arguments. In the example a "
"new tuple was created to serve as the argument list, which is :c:func:"
"`Py_DECREF`\\ -ed immediately after the :c:func:`PyObject_CallObject` call."
msgstr ""
#: ../../extending/extending.rst:568
msgid ""
"The return value of :c:func:`PyObject_CallObject` is \"new\": either it is a "
"brand new object, or it is an existing object whose reference count has been "
"incremented. So, unless you want to save it in a global variable, you "
"should somehow :c:func:`Py_DECREF` the result, even (especially!) if you are "
"not interested in its value."
msgstr ""
#: ../../extending/extending.rst:574
msgid ""
"Before you do this, however, it is important to check that the return value "
"isn't ``NULL``. If it is, the Python function terminated by raising an "
"exception. If the C code that called :c:func:`PyObject_CallObject` is called "
"from Python, it should now return an error indication to its Python caller, "
"so the interpreter can print a stack trace, or the calling Python code can "
"handle the exception. If this is not possible or desirable, the exception "
"should be cleared by calling :c:func:`PyErr_Clear`. For example::"
msgstr ""
#: ../../extending/extending.rst:587
msgid ""
"Depending on the desired interface to the Python callback function, you may "
"also have to provide an argument list to :c:func:`PyObject_CallObject`. In "
"some cases the argument list is also provided by the Python program, through "
"the same interface that specified the callback function. It can then be "
"saved and used in the same manner as the function object. In other cases, "
"you may have to construct a new tuple to pass as the argument list. The "
"simplest way to do this is to call :c:func:`Py_BuildValue`. For example, if "
"you want to pass an integral event code, you might use the following code::"
msgstr ""
#: ../../extending/extending.rst:606
msgid ""
"Note the placement of ``Py_DECREF(arglist)`` immediately after the call, "
"before the error check! Also note that strictly speaking this code is not "
"complete: :c:func:`Py_BuildValue` may run out of memory, and this should be "
"checked."
msgstr ""
#: ../../extending/extending.rst:610
msgid ""
"You may also call a function with keyword arguments by using :c:func:"
"`PyObject_Call`, which supports arguments and keyword arguments. As in the "
"above example, we use :c:func:`Py_BuildValue` to construct the dictionary. ::"
msgstr ""
#: ../../extending/extending.rst:628
msgid "Extracting Parameters in Extension Functions"
msgstr ""
#: ../../extending/extending.rst:632
msgid "The :c:func:`PyArg_ParseTuple` function is declared as follows::"
msgstr ""
#: ../../extending/extending.rst:636
msgid ""
"The *arg* argument must be a tuple object containing an argument list passed "
"from Python to a C function. The *format* argument must be a format string, "
"whose syntax is explained in :ref:`arg-parsing` in the Python/C API "
"Reference Manual. The remaining arguments must be addresses of variables "
"whose type is determined by the format string."
msgstr ""
#: ../../extending/extending.rst:642
msgid ""
"Note that while :c:func:`PyArg_ParseTuple` checks that the Python arguments "
"have the required types, it cannot check the validity of the addresses of C "
"variables passed to the call: if you make mistakes there, your code will "
"probably crash or at least overwrite random bits in memory. So be careful!"
msgstr ""
#: ../../extending/extending.rst:647
msgid ""
"Note that any Python object references which are provided to the caller are "
"*borrowed* references; do not decrement their reference count!"
msgstr ""
#: ../../extending/extending.rst:650
msgid "Some example calls::"
msgstr ""
"一些呼叫範例：\n"
"\n"
"::"
#: ../../extending/extending.rst:720
msgid "Keyword Parameters for Extension Functions"
msgstr ""
#: ../../extending/extending.rst:724
msgid ""
"The :c:func:`PyArg_ParseTupleAndKeywords` function is declared as follows::"
msgstr ""
#: ../../extending/extending.rst:729
msgid ""
"The *arg* and *format* parameters are identical to those of the :c:func:"
"`PyArg_ParseTuple` function. The *kwdict* parameter is the dictionary of "
"keywords received as the third parameter from the Python runtime. The "
"*kwlist* parameter is a ``NULL``-terminated list of strings which identify "
"the parameters; the names are matched with the type information from "
"*format* from left to right. On success, :c:func:"
"`PyArg_ParseTupleAndKeywords` returns true, otherwise it returns false and "
"raises an appropriate exception."
msgstr ""
#: ../../extending/extending.rst:739
msgid ""
"Nested tuples cannot be parsed when using keyword arguments! Keyword "
"parameters passed in which are not present in the *kwlist* will cause :exc:"
"`TypeError` to be raised."
msgstr ""
#: ../../extending/extending.rst:745
msgid ""
"Here is an example module which uses keywords, based on an example by Geoff "
"Philbrick (philbrick@hks.com)::"
msgstr ""
#: ../../extending/extending.rst:800
msgid "Building Arbitrary Values"
msgstr ""
#: ../../extending/extending.rst:802
msgid ""
"This function is the counterpart to :c:func:`PyArg_ParseTuple`. It is "
"declared as follows::"
msgstr ""
#: ../../extending/extending.rst:807
msgid ""
"It recognizes a set of format units similar to the ones recognized by :c:"
"func:`PyArg_ParseTuple`, but the arguments (which are input to the function, "
"not output) must not be pointers, just values. It returns a new Python "
"object, suitable for returning from a C function called from Python."
msgstr ""
#: ../../extending/extending.rst:812
msgid ""
"One difference with :c:func:`PyArg_ParseTuple`: while the latter requires "
"its first argument to be a tuple (since Python argument lists are always "
"represented as tuples internally), :c:func:`Py_BuildValue` does not always "
"build a tuple. It builds a tuple only if its format string contains two or "
"more format units. If the format string is empty, it returns ``None``; if it "
"contains exactly one format unit, it returns whatever object is described by "
"that format unit. To force it to return a tuple of size 0 or one, "
"parenthesize the format string."
msgstr ""
#: ../../extending/extending.rst:820
msgid ""
"Examples (to the left the call, to the right the resulting Python value):"
msgstr ""
#: ../../extending/extending.rst:846
msgid "Reference Counts"
msgstr ""
#: ../../extending/extending.rst:848
msgid ""
"In languages like C or C++, the programmer is responsible for dynamic "
"allocation and deallocation of memory on the heap. In C, this is done using "
"the functions :c:func:`malloc` and :c:func:`free`. In C++, the operators "
"``new`` and ``delete`` are used with essentially the same meaning and we'll "
"restrict the following discussion to the C case."
msgstr ""
#: ../../extending/extending.rst:854
msgid ""
"Every block of memory allocated with :c:func:`malloc` should eventually be "
"returned to the pool of available memory by exactly one call to :c:func:"
"`free`. It is important to call :c:func:`free` at the right time. If a "
"block's address is forgotten but :c:func:`free` is not called for it, the "
"memory it occupies cannot be reused until the program terminates. This is "
"called a :dfn:`memory leak`. On the other hand, if a program calls :c:func:"
"`free` for a block and then continues to use the block, it creates a "
"conflict with re-use of the block through another :c:func:`malloc` call. "
"This is called :dfn:`using freed memory`. It has the same bad consequences "
"as referencing uninitialized data --- core dumps, wrong results, mysterious "
"crashes."
msgstr ""
#: ../../extending/extending.rst:865
msgid ""
"Common causes of memory leaks are unusual paths through the code. For "
"instance, a function may allocate a block of memory, do some calculation, "
"and then free the block again. Now a change in the requirements for the "
"function may add a test to the calculation that detects an error condition "
"and can return prematurely from the function. It's easy to forget to free "
"the allocated memory block when taking this premature exit, especially when "
"it is added later to the code. Such leaks, once introduced, often go "
"undetected for a long time: the error exit is taken only in a small fraction "
"of all calls, and most modern machines have plenty of virtual memory, so the "
"leak only becomes apparent in a long-running process that uses the leaking "
"function frequently. Therefore, it's important to prevent leaks from "
"happening by having a coding convention or strategy that minimizes this kind "
"of errors."
msgstr ""
#: ../../extending/extending.rst:878
msgid ""
"Since Python makes heavy use of :c:func:`malloc` and :c:func:`free`, it "
"needs a strategy to avoid memory leaks as well as the use of freed memory. "
"The chosen method is called :dfn:`reference counting`. The principle is "
"simple: every object contains a counter, which is incremented when a "
"reference to the object is stored somewhere, and which is decremented when a "
"reference to it is deleted. When the counter reaches zero, the last "
"reference to the object has been deleted and the object is freed."
msgstr ""
#: ../../extending/extending.rst:886
msgid ""
"An alternative strategy is called :dfn:`automatic garbage collection`. "
"(Sometimes, reference counting is also referred to as a garbage collection "
"strategy, hence my use of \"automatic\" to distinguish the two.) The big "
"advantage of automatic garbage collection is that the user doesn't need to "
"call :c:func:`free` explicitly. (Another claimed advantage is an "
"improvement in speed or memory usage --- this is no hard fact however.) The "
"disadvantage is that for C, there is no truly portable automatic garbage "
"collector, while reference counting can be implemented portably (as long as "
"the functions :c:func:`malloc` and :c:func:`free` are available --- which "
"the C Standard guarantees). Maybe some day a sufficiently portable automatic "
"garbage collector will be available for C. Until then, we'll have to live "
"with reference counts."
msgstr ""
#: ../../extending/extending.rst:898
msgid ""
"While Python uses the traditional reference counting implementation, it also "
"offers a cycle detector that works to detect reference cycles. This allows "
"applications to not worry about creating direct or indirect circular "
"references; these are the weakness of garbage collection implemented using "
"only reference counting. Reference cycles consist of objects which contain "
"(possibly indirect) references to themselves, so that each object in the "
"cycle has a reference count which is non-zero. Typical reference counting "
"implementations are not able to reclaim the memory belonging to any objects "
"in a reference cycle, or referenced from the objects in the cycle, even "
"though there are no further references to the cycle itself."
msgstr ""
#: ../../extending/extending.rst:909
msgid ""
"The cycle detector is able to detect garbage cycles and can reclaim them. "
"The :mod:`gc` module exposes a way to run the detector (the :func:`~gc."
"collect` function), as well as configuration interfaces and the ability to "
"disable the detector at runtime."
msgstr ""
#: ../../extending/extending.rst:918
msgid "Reference Counting in Python"
msgstr ""
#: ../../extending/extending.rst:920
msgid ""
"There are two macros, ``Py_INCREF(x)`` and ``Py_DECREF(x)``, which handle "
"the incrementing and decrementing of the reference count. :c:func:"
"`Py_DECREF` also frees the object when the count reaches zero. For "
"flexibility, it doesn't call :c:func:`free` directly --- rather, it makes a "
"call through a function pointer in the object's :dfn:`type object`. For "
"this purpose (and others), every object also contains a pointer to its type "
"object."
msgstr ""
#: ../../extending/extending.rst:927
msgid ""
"The big question now remains: when to use ``Py_INCREF(x)`` and "
"``Py_DECREF(x)``? Let's first introduce some terms. Nobody \"owns\" an "
"object; however, you can :dfn:`own a reference` to an object. An object's "
"reference count is now defined as the number of owned references to it. The "
"owner of a reference is responsible for calling :c:func:`Py_DECREF` when the "
"reference is no longer needed. Ownership of a reference can be "
"transferred. There are three ways to dispose of an owned reference: pass it "
"on, store it, or call :c:func:`Py_DECREF`. Forgetting to dispose of an owned "
"reference creates a memory leak."
msgstr ""
#: ../../extending/extending.rst:936
msgid ""
"It is also possible to :dfn:`borrow` [#]_ a reference to an object. The "
"borrower of a reference should not call :c:func:`Py_DECREF`. The borrower "
"must not hold on to the object longer than the owner from which it was "
"borrowed. Using a borrowed reference after the owner has disposed of it "
"risks using freed memory and should be avoided completely [#]_."
msgstr ""
#: ../../extending/extending.rst:942
msgid ""
"The advantage of borrowing over owning a reference is that you don't need to "
"take care of disposing of the reference on all possible paths through the "
"code --- in other words, with a borrowed reference you don't run the risk of "
"leaking when a premature exit is taken. The disadvantage of borrowing over "
"owning is that there are some subtle situations where in seemingly correct "
"code a borrowed reference can be used after the owner from which it was "
"borrowed has in fact disposed of it."
msgstr ""
#: ../../extending/extending.rst:950
msgid ""
"A borrowed reference can be changed into an owned reference by calling :c:"
"func:`Py_INCREF`. This does not affect the status of the owner from which "
"the reference was borrowed --- it creates a new owned reference, and gives "
"full owner responsibilities (the new owner must dispose of the reference "
"properly, as well as the previous owner)."
msgstr ""
#: ../../extending/extending.rst:960
msgid "Ownership Rules"
msgstr ""
#: ../../extending/extending.rst:962
msgid ""
"Whenever an object reference is passed into or out of a function, it is part "
"of the function's interface specification whether ownership is transferred "
"with the reference or not."
msgstr ""
#: ../../extending/extending.rst:966
msgid ""
"Most functions that return a reference to an object pass on ownership with "
"the reference. In particular, all functions whose function it is to create "
"a new object, such as :c:func:`PyLong_FromLong` and :c:func:`Py_BuildValue`, "
"pass ownership to the receiver. Even if the object is not actually new, you "
"still receive ownership of a new reference to that object. For instance, :c:"
"func:`PyLong_FromLong` maintains a cache of popular values and can return a "
"reference to a cached item."
msgstr ""
#: ../../extending/extending.rst:974
msgid ""
"Many functions that extract objects from other objects also transfer "
"ownership with the reference, for instance :c:func:"
"`PyObject_GetAttrString`. The picture is less clear, here, however, since a "
"few common routines are exceptions: :c:func:`PyTuple_GetItem`, :c:func:"
"`PyList_GetItem`, :c:func:`PyDict_GetItem`, and :c:func:"
"`PyDict_GetItemString` all return references that you borrow from the tuple, "
"list or dictionary."
msgstr ""
#: ../../extending/extending.rst:981
msgid ""
"The function :c:func:`PyImport_AddModule` also returns a borrowed reference, "
"even though it may actually create the object it returns: this is possible "
"because an owned reference to the object is stored in ``sys.modules``."
msgstr ""
#: ../../extending/extending.rst:985
msgid ""
"When you pass an object reference into another function, in general, the "
"function borrows the reference from you --- if it needs to store it, it will "
"use :c:func:`Py_INCREF` to become an independent owner. There are exactly "
"two important exceptions to this rule: :c:func:`PyTuple_SetItem` and :c:func:"
"`PyList_SetItem`. These functions take over ownership of the item passed to "
"them --- even if they fail! (Note that :c:func:`PyDict_SetItem` and friends "
"don't take over ownership --- they are \"normal.\")"
msgstr ""
#: ../../extending/extending.rst:993
msgid ""
"When a C function is called from Python, it borrows references to its "
"arguments from the caller. The caller owns a reference to the object, so "
"the borrowed reference's lifetime is guaranteed until the function returns. "
"Only when such a borrowed reference must be stored or passed on, it must be "
"turned into an owned reference by calling :c:func:`Py_INCREF`."
msgstr ""
#: ../../extending/extending.rst:999
msgid ""
"The object reference returned from a C function that is called from Python "
"must be an owned reference --- ownership is transferred from the function to "
"its caller."
msgstr ""
#: ../../extending/extending.rst:1007
msgid "Thin Ice"
msgstr ""
#: ../../extending/extending.rst:1009
msgid ""
"There are a few situations where seemingly harmless use of a borrowed "
"reference can lead to problems. These all have to do with implicit "
"invocations of the interpreter, which can cause the owner of a reference to "
"dispose of it."
msgstr ""
#: ../../extending/extending.rst:1013
msgid ""
"The first and most important case to know about is using :c:func:`Py_DECREF` "
"on an unrelated object while borrowing a reference to a list item. For "
"instance::"
msgstr ""
#: ../../extending/extending.rst:1025
msgid ""
"This function first borrows a reference to ``list[0]``, then replaces "
"``list[1]`` with the value ``0``, and finally prints the borrowed reference. "
"Looks harmless, right? But it's not!"
msgstr ""
#: ../../extending/extending.rst:1029
msgid ""
"Let's follow the control flow into :c:func:`PyList_SetItem`. The list owns "
"references to all its items, so when item 1 is replaced, it has to dispose "
"of the original item 1. Now let's suppose the original item 1 was an "
"instance of a user-defined class, and let's further suppose that the class "
"defined a :meth:`!__del__` method. If this class instance has a reference "
"count of 1, disposing of it will call its :meth:`!__del__` method."
msgstr ""
#: ../../extending/extending.rst:1036
msgid ""
"Since it is written in Python, the :meth:`!__del__` method can execute "
"arbitrary Python code. Could it perhaps do something to invalidate the "
"reference to ``item`` in :c:func:`!bug`? You bet! Assuming that the list "
"passed into :c:func:`!bug` is accessible to the :meth:`!__del__` method, it "
"could execute a statement to the effect of ``del list[0]``, and assuming "