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1385 lines (1219 loc) · 51.4 KB
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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: 2026-08-15 14:15+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 "Using the C API: Assorted topics"
msgstr ""
msgid ""
"The :ref:`tutorial <first-extension-module>` walked you through creating a C "
"API extension module, but left many areas unexplained. This document looks "
"at several concepts that you'll need to learn in order to write more complex "
"extensions."
msgstr ""
msgid "Errors and Exceptions"
msgstr ""
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 ""
msgid ""
"The Python API defines a number of functions to set various types of "
"exceptions."
msgstr ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
msgid ""
"You can also define a new exception that is unique to your module. The "
"simplest way to do this is to declare a static global object variable at the "
"beginning of the file::"
msgstr ""
msgid "static PyObject *SpamError = NULL;"
msgstr ""
msgid ""
"and initialize it by calling :c:func:`PyErr_NewException` in the module's :c:"
"data:`Py_mod_exec` function (:c:func:`!spam_module_exec`)::"
msgstr ""
msgid "SpamError = PyErr_NewException(\"spam.error\", NULL, NULL);"
msgstr ""
msgid ""
"Since :c:data:`!SpamError` is a global variable, it will be overwritten "
"every time the module is reinitialized, when the :c:data:`Py_mod_exec` "
"function is called."
msgstr ""
msgid ""
"For now, let's avoid the issue: we will block repeated initialization by "
"raising an :py:exc:`ImportError`::"
msgstr ""
msgid ""
"static PyObject *SpamError = NULL;\n"
"\n"
"static int\n"
"spam_module_exec(PyObject *m)\n"
"{\n"
" if (SpamError != NULL) {\n"
" PyErr_SetString(PyExc_ImportError,\n"
" \"cannot initialize spam module more than once\");\n"
" return -1;\n"
" }\n"
" SpamError = PyErr_NewException(\"spam.error\", NULL, NULL);\n"
" if (PyModule_AddObjectRef(m, \"SpamError\", SpamError) < 0) {\n"
" return -1;\n"
" }\n"
"\n"
" return 0;\n"
"}\n"
"\n"
"static PyModuleDef_Slot spam_module_slots[] = {\n"
" {Py_mod_exec, spam_module_exec},\n"
" {0, NULL}\n"
"};\n"
"\n"
"static struct PyModuleDef spam_module = {\n"
" .m_base = PyModuleDef_HEAD_INIT,\n"
" .m_name = \"spam\",\n"
" .m_size = 0, // non-negative\n"
" .m_slots = spam_module_slots,\n"
"};\n"
"\n"
"PyMODINIT_FUNC\n"
"PyInit_spam(void)\n"
"{\n"
" return PyModuleDef_Init(&spam_module);\n"
"}"
msgstr ""
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 ""
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 ""
msgid ""
"For now, the :c:func:`Py_DECREF` call to remove this reference is missing. "
"Even when the Python interpreter shuts down, the global :c:data:`!SpamError` "
"variable will not be garbage-collected. It will \"leak\". We did, however, "
"ensure that this will happen at most once per process."
msgstr ""
msgid ""
"We discuss the use of :c:macro:`PyMODINIT_FUNC` as a function return type "
"later in this sample."
msgstr ""
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 ""
msgid ""
"static PyObject *\n"
"spam_system(PyObject *self, PyObject *args)\n"
"{\n"
" const char *command;\n"
" int sts;\n"
"\n"
" if (!PyArg_ParseTuple(args, \"s\", &command))\n"
" return NULL;\n"
" sts = system(command);\n"
" if (sts < 0) {\n"
" PyErr_SetString(SpamError, \"System command failed\");\n"
" return NULL;\n"
" }\n"
" return PyLong_FromLong(sts);\n"
"}"
msgstr ""
msgid "Embedding an extension"
msgstr ""
msgid ""
"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. On Unix, 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 ""
msgid "spam spammodule.o"
msgstr ""
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 ""
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 ""
msgid "spam spammodule.o -lX11"
msgstr ""
msgid "Calling Python Functions from C"
msgstr ""
msgid ""
"The tutorial 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 ""
msgid ""
"Fortunately, the Python interpreter is easily called recursively, and there "
"is a standard interface to call a Python function. (If you're interested in "
"how to call the Python parser with a particular string as input, see :ref:"
"`veryhigh`.)"
msgstr ""
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 ""
msgid ""
"static PyObject *my_callback = NULL;\n"
"\n"
"static PyObject *\n"
"my_set_callback(PyObject *dummy, PyObject *args)\n"
"{\n"
" PyObject *result = NULL;\n"
" PyObject *temp;\n"
"\n"
" if (PyArg_ParseTuple(args, \"O:set_callback\", &temp)) {\n"
" if (!PyCallable_Check(temp)) {\n"
" PyErr_SetString(PyExc_TypeError, \"parameter must be "
"callable\");\n"
" return NULL;\n"
" }\n"
" Py_XINCREF(temp); /* Add a reference to new callback */\n"
" Py_XDECREF(my_callback); /* Dispose of previous callback */\n"
" my_callback = temp; /* Remember new callback */\n"
" /* Boilerplate to return \"None\" */\n"
" Py_INCREF(Py_None);\n"
" result = Py_None;\n"
" }\n"
" return result;\n"
"}"
msgstr ""
msgid ""
"This function must be registered with the interpreter using the :c:macro:"
"`METH_VARARGS` flag in :c:type:`PyMethodDef.ml_flags`. The :c:func:"
"`PyArg_ParseTuple` function and its arguments are documented in section :ref:"
"`parsetuple`."
msgstr ""
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 ""
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 ""
msgid ""
"int arg;\n"
"PyObject *arglist;\n"
"PyObject *result;\n"
"...\n"
"arg = 123;\n"
"...\n"
"/* Time to call the callback */\n"
"arglist = Py_BuildValue(\"(i)\", arg);\n"
"result = PyObject_CallObject(my_callback, arglist);\n"
"Py_DECREF(arglist);"
msgstr ""
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 ""
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 ""
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 ""
msgid ""
"if (result == NULL)\n"
" return NULL; /* Pass error back */\n"
"...use result...\n"
"Py_DECREF(result);"
msgstr ""
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 ""
msgid ""
"PyObject *arglist;\n"
"...\n"
"arglist = Py_BuildValue(\"(l)\", eventcode);\n"
"result = PyObject_CallObject(my_callback, arglist);\n"
"Py_DECREF(arglist);\n"
"if (result == NULL)\n"
" return NULL; /* Pass error back */\n"
"/* Here maybe use the result */\n"
"Py_DECREF(result);"
msgstr ""
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 ""
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 ""
msgid ""
"PyObject *dict;\n"
"...\n"
"dict = Py_BuildValue(\"{s:i}\", \"name\", val);\n"
"result = PyObject_Call(my_callback, NULL, dict);\n"
"Py_DECREF(dict);\n"
"if (result == NULL)\n"
" return NULL; /* Pass error back */\n"
"/* Here maybe use the result */\n"
"Py_DECREF(result);"
msgstr ""
msgid "Extracting Parameters in Extension Functions"
msgstr ""
msgid ""
"The :ref:`tutorial <first-extension-module>` uses a \":c:data:`METH_O`\" "
"function, which is limited to a single Python argument. If you want more, "
"you can use :c:data:`METH_VARARGS` instead. With this flag, the C function "
"will receive a :py:class:`tuple` of arguments instead of a single object."
msgstr ""
msgid ""
"For unpacking the tuple, CPython provides the :c:func:`PyArg_ParseTuple` "
"function, declared as follows::"
msgstr ""
msgid "int PyArg_ParseTuple(PyObject *arg, const char *format, ...);"
msgstr ""
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 ""
msgid ""
"For example, to receive a single Python :py:class:`str` object and turn it "
"into a C buffer, you would use ``\"s\"`` as the format string::"
msgstr ""
msgid ""
"const char *command;\n"
"if (!PyArg_ParseTuple(args, \"s\", &command)) {\n"
" return NULL;\n"
"}"
msgstr ""
msgid ""
"If an error is detected in the argument list, :c:func:`!PyArg_ParseTuple` "
"returns ``NULL`` (the error indicator for functions returning object "
"pointers); your function may return ``NULL``, relying on the exception set "
"by :c:func:`PyArg_ParseTuple`."
msgstr ""
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 ""
msgid ""
"Note that any Python object references which are provided to the caller are "
"*borrowed* references; do not decrement their reference count!"
msgstr ""
msgid "Some example calls::"
msgstr ""
msgid "#include <Python.h>"
msgstr ""
msgid ""
"int ok;\n"
"int i, j;\n"
"long k, l;\n"
"const char *s;\n"
"Py_ssize_t size;\n"
"\n"
"ok = PyArg_ParseTuple(args, \"\"); /* No arguments */\n"
" /* Python call: f() */"
msgstr ""
msgid ""
"ok = PyArg_ParseTuple(args, \"s\", &s); /* A string */\n"
" /* Possible Python call: f('whoops!') */"
msgstr ""
msgid ""
"ok = PyArg_ParseTuple(args, \"lls\", &k, &l, &s); /* Two longs and a string "
"*/\n"
" /* Possible Python call: f(1, 2, 'three') */"
msgstr ""
msgid ""
"ok = PyArg_ParseTuple(args, \"(ii)s#\", &i, &j, &s, &size);\n"
" /* A pair of ints and a string, whose size is also returned */\n"
" /* Possible Python call: f((1, 2), 'three') */"
msgstr ""
msgid ""
"{\n"
" const char *file;\n"
" const char *mode = \"r\";\n"
" int bufsize = 0;\n"
" ok = PyArg_ParseTuple(args, \"s|si\", &file, &mode, &bufsize);\n"
" /* A string, and optionally another string and an integer */\n"
" /* Possible Python calls:\n"
" f('spam')\n"
" f('spam', 'w')\n"
" f('spam', 'wb', 100000) */\n"
"}"
msgstr ""
msgid ""
"{\n"
" int left, top, right, bottom, h, v;\n"
" ok = PyArg_ParseTuple(args, \"((ii)(ii))(ii)\",\n"
" &left, &top, &right, &bottom, &h, &v);\n"
" /* A rectangle and a point */\n"
" /* Possible Python call:\n"
" f(((0, 0), (400, 300)), (10, 10)) */\n"
"}"
msgstr ""
msgid ""
"{\n"
" Py_complex c;\n"
" ok = PyArg_ParseTuple(args, \"D:myfunction\", &c);\n"
" /* a complex, also providing a function name for errors */\n"
" /* Possible Python call: myfunction(1+2j) */\n"
"}"
msgstr ""
msgid "Keyword Parameters for Extension Functions"
msgstr ""
msgid ""
"If you also want your function to accept :term:`keyword arguments <keyword "
"argument>`, use the :c:data:`METH_KEYWORDS` flag in combination with :c:data:"
"`METH_VARARGS`. (:c:data:`!METH_KEYWORDS` can also be used with other flags; "
"see its documentation for the allowed combinations.)"
msgstr ""
msgid ""
"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 ""
msgid ""
"The :c:func:`PyArg_ParseTupleAndKeywords` function is declared as follows::"
msgstr ""
msgid ""
"int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict,\n"
" const char *format, char * const "
"*kwlist, ...);"
msgstr ""
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 ""
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 ""
msgid ""
"Here is an example module which uses keywords, based on an example by Geoff "
"Philbrick (philbrick@hks.com)::"
msgstr ""
msgid ""
"#define PY_SSIZE_T_CLEAN\n"
"#include <Python.h>\n"
"\n"
"static PyObject *\n"
"keywdarg_parrot(PyObject *self, PyObject *args, PyObject *keywds)\n"
"{\n"
" int voltage;\n"
" const char *state = \"a stiff\";\n"
" const char *action = \"voom\";\n"
" const char *type = \"Norwegian Blue\";\n"
"\n"
" static char *kwlist[] = {\"voltage\", \"state\", \"action\", \"type\", "
"NULL};\n"
"\n"
" if (!PyArg_ParseTupleAndKeywords(args, keywds, \"i|sss\", kwlist,\n"
" &voltage, &state, &action, &type))\n"
" return NULL;\n"
"\n"
" printf(\"-- This parrot wouldn't %s if you put %i Volts through it."
"\\n\",\n"
" action, voltage);\n"
" printf(\"-- Lovely plumage, the %s -- It's %s!\\n\", type, state);\n"
"\n"
" Py_RETURN_NONE;\n"
"}\n"
"\n"
"static PyMethodDef keywdarg_methods[] = {\n"
" /* The cast of the function is necessary since PyCFunction values\n"
" * only take two PyObject* parameters, and keywdarg_parrot() takes\n"
" * three.\n"
" */\n"
" {\"parrot\", (PyCFunction)(void(*)(void))keywdarg_parrot, METH_VARARGS | "
"METH_KEYWORDS,\n"
" \"Print a lovely skit to standard output.\"},\n"
" {NULL, NULL, 0, NULL} /* sentinel */\n"
"};"
msgstr ""
msgid "Building Arbitrary Values"
msgstr ""
msgid ""
"This function is the counterpart to :c:func:`PyArg_ParseTuple`. It is "
"declared as follows::"
msgstr ""
msgid "PyObject *Py_BuildValue(const char *format, ...);"
msgstr ""
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 ""
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 ""
msgid ""
"Examples (to the left the call, to the right the resulting Python value):"
msgstr ""
msgid ""
"Py_BuildValue(\"\") None\n"
"Py_BuildValue(\"i\", 123) 123\n"
"Py_BuildValue(\"iii\", 123, 456, 789) (123, 456, 789)\n"
"Py_BuildValue(\"s\", \"hello\") 'hello'\n"
"Py_BuildValue(\"y\", \"hello\") b'hello'\n"
"Py_BuildValue(\"ss\", \"hello\", \"world\") ('hello', 'world')\n"
"Py_BuildValue(\"s#\", \"hello\", 4) 'hell'\n"
"Py_BuildValue(\"y#\", \"hello\", 4) b'hell'\n"
"Py_BuildValue(\"()\") ()\n"
"Py_BuildValue(\"(i)\", 123) (123,)\n"
"Py_BuildValue(\"(ii)\", 123, 456) (123, 456)\n"
"Py_BuildValue(\"(i,i)\", 123, 456) (123, 456)\n"
"Py_BuildValue(\"[i,i]\", 123, 456) [123, 456]\n"
"Py_BuildValue(\"{s:i,s:i}\",\n"
" \"abc\", 123, \"def\", 456) {'abc': 123, 'def': 456}\n"
"Py_BuildValue(\"((ii)(ii)) (ii)\",\n"
" 1, 2, 3, 4, 5, 6) (((1, 2), (3, 4)), (5, 6))"
msgstr ""
msgid "Reference Counts"
msgstr ""
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 ""
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 reuse 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 ""
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 ""
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 ""
msgid ""
"An alternative strategy is called :dfn:`automatic garbage collection`. "
"(Sometimes, reference counting is also referred to as a garbage collection "
"strategy, hence the 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 ""
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 ""
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 ""
msgid "Reference Counting in Python"
msgstr ""
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 ""
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 ""
msgid ""
"It is also possible to :dfn:`borrow` [#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 [#dont-check-"
"refcount]_."
msgstr ""
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 ""
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 ""
msgid "Ownership Rules"
msgstr ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
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 ""
msgid "Thin Ice"
msgstr ""
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 ""
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 ""
msgid ""
"void\n"
"bug(PyObject *list)\n"
"{\n"
" PyObject *item = PyList_GetItem(list, 0);\n"
"\n"
" PyList_SetItem(list, 1, PyLong_FromLong(0L));\n"
" PyObject_Print(item, stdout, 0); /* BUG! */\n"
"}"
msgstr ""
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 ""
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. "
"Internally, :c:func:`PyList_SetItem` calls :c:func:`Py_DECREF` on the "
"replaced item, which invokes replaced item's corresponding :c:member:"
"`~PyTypeObject.tp_dealloc` function. During deallocation, :c:member:"
"`~PyTypeObject.tp_dealloc` calls :c:member:`~PyTypeObject.tp_finalize`, "
"which is mapped to the :meth:`!__del__` method for class instances (see :pep:"
"`442`). This entire sequence happens synchronously within the :c:func:"
"`PyList_SetItem` call."
msgstr ""
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 "
"this was the last reference to that object, it would free the memory "
"associated with it, thereby invalidating ``item``."
msgstr ""
msgid ""
"The solution, once you know the source of the problem, is easy: temporarily "
"increment the reference count. The correct version of the function reads::"
msgstr ""
msgid ""
"void\n"
"no_bug(PyObject *list)\n"
"{\n"
" PyObject *item = PyList_GetItem(list, 0);\n"
"\n"
" Py_INCREF(item);\n"
" PyList_SetItem(list, 1, PyLong_FromLong(0L));\n"
" PyObject_Print(item, stdout, 0);\n"
" Py_DECREF(item);\n"
"}"
msgstr ""