Analyse des arguments et construction des valeurs¶

Ces fonctions sont utiles pour créer vos propres fonctions et méthodes d'extensions. Des informations supplémentaires et des exemples sont disponibles ici: Extension et intégration de l'interpréteur Python.

Dans Les trois premières de ces fonctions décrites, PyArg_ParseTuple(), PyArg_ParseTupleAndKeywords(), et PyArg_Parse(), toutes utilisent des chaînes de format qui sont utilisées pour indiquer à la fonction les arguments attendus. Les chaînes de format utilise la même syntaxe pour chacune de ces fonctions.

Analyse des arguments¶

Une chaîne de format se compose de zéro ou plusieurs "unités de format". Une unité de format décrit un objet Python, elle est généralement composée d'un seul caractère ou d'une séquence d'unités de format entre parenthèses. À quelques exceptions près, une unité de format qui n'est pas une séquence entre parenthèses correspond normalement à un argument d'une seule adresse pour ces fonctions. Dans la description qui suit, la forme entre guillemets est l'unité de format, l'entrée entre parenthèses est le type d'objet Python qui correspond à l'unité de format, et l'entrée entre crochets est le type de la variable C (ou des variables) dont l'adresse doit être donnée.

Chaînes et tampons¶

Ces formats permettent d'accéder à un objet sous forme d'un fragment de mémoire contiguë. Il n'est pas nécessaire d'allouer la mémoire pour l'unicode ou le bytes renvoyé.

Sauf indication contraire, les tampons ne se terminent pas par NUL.

There are three ways strings and buffers can be converted to C:

Formats such as y* and s* fill a Py_buffer structure. This locks the underlying buffer so that the caller can subsequently use the buffer even inside a Py_BEGIN_ALLOW_THREADS block without the risk of mutable data being resized or destroyed. As a result, you have to call PyBuffer_Release() after you have finished processing the data (or in any early abort case).
The es, es#, et and et# formats allocate the result buffer. You have to call PyMem_Free() after you have finished processing the data (or in any early abort case).
Other formats take a str or a read-only bytes-like object, such as bytes, and provide a const char * pointer to its buffer. In this case the buffer is "borrowed": it is managed by the corresponding Python object, and shares the lifetime of this object. You won't have to release any memory yourself.

To ensure that the underlying buffer may be safely borrowed, the object's PyBufferProcs.bf_releasebuffer field must be NULL. This disallows common mutable objects such as bytearray, but also some read-only objects such as memoryview of bytes.

Besides this bf_releasebuffer requirement, there is no check to verify whether the input object is immutable (e.g. whether it would honor a request for a writable buffer, or whether another thread can mutate the data).

Note

For all # variants of formats (s#, y#, etc.), the macro PY_SSIZE_T_CLEAN must be defined before including Python.h. On Python 3.9 and older, the type of the length argument is Py_ssize_t if the PY_SSIZE_T_CLEAN macro is defined, or int otherwise.

s (str) [const char *]

Convertit un objet Unicode en un pointeur vers une chaîne de caractères. S'il s'agit d'un pointeur vers une chaîne de caractères déjà existante, il est stocké dans la variable de type pointeur vers un caractère dont vous avez donné l'adresse. Une chaîne de caractères en C se termine par NULL. La chaîne de caractères Python ne doit donc pas contenir de caractère dont le code est null. Si elle en contient, une exception ValueError est levée. Si la conversion échoue, une UnicodeError est levée.

Note

Ce format n'accepte pas les objets compatibles avec une chaîne d'octets. Si vous voulez accepter les chemins du système de fichiers et les convertir vers des chaînes de caractères C, il est préférable d'utiliser le format O& avec PyUnicode_FSConverter() en tant que converter.

Modifié dans la version 3.5: Auparavant, une TypeError était levée quand la chaîne de caractères Python contenait des codes NULL.

s* (str ou bytes-like object) [Py_buffer]

Ce format accepte les objets Unicode et les bytes-like object. Cela remplit une structure Py_buffer qui est fournie par l'appelant. Dans ce cas, la chaîne de caractères C qui en résulte peut contenir des octets NULL. Les objets Unicode sont convertis en chaînes de caractères C en utilisant l'encodage 'utf-8'.

s# (str, read-only bytes-like object) [const char *, Py_ssize_t]

Like s*, except that it provides a borrowed buffer. The result is stored into two C variables, the first one a pointer to a C string, the second one its length. The string may contain embedded null bytes. Unicode objects are converted to C strings using 'utf-8' encoding.

z (str ou None) [const char *]

Like s, but the Python object may also be None, in which case the C pointer is set to NULL.

z* (str, bytes-like object ou None) [Py_buffer]

Comme s*, mais l'objet Python peut aussi être None, auquel cas le membre buf, dont la structure est Py_buffer est fixée à NULL.

z# (str, read-only bytes-like object or None) [const char *, Py_ssize_t]

Like s#, but the Python object may also be None, in which case the C pointer is set to NULL.

y (lecture seule objet compatible avec une chaîne d'octets) [constante char *]

This format converts a bytes-like object to a C pointer to a borrowed character string; it does not accept Unicode objects. The bytes buffer must not contain embedded null bytes; if it does, a ValueError exception is raised.

Modifié dans la version 3.5: Auparavant, TypeError était levée lorsque des octets null étaient rencontrés dans le tampon d'octets.

y* (bytes-like object) [Py_buffer]

This variant on s* doesn't accept Unicode objects, only bytes-like objects. This is the recommended way to accept binary data.

y# (read-only bytes-like object) [const char *, Py_ssize_t]

Cette variante de s# n'accepte pas les objets Unicode, uniquement des objets assimilés à des octets.

S (bytes) [PyBytesObject *]

Requires that the Python object is a bytes object, without attempting any conversion. Raises TypeError if the object is not a bytes object. The C variable may also be declared as PyObject*.

Y (bytearray) [PyByteArrayObject *]

Requires that the Python object is a bytearray object, without attempting any conversion. Raises TypeError if the object is not a bytearray object. The C variable may also be declared as PyObject*.

u (str) [const Py_UNICODE *]

Convertit un objet Python Unicode en un pointeur C vers un tampon de caractères Unicode terminé par NULL. Vous devez passer l'adresse d'un pointeur Py_UNICODE, qui sera rempli avec le pointeur vers un tampon Unicode existant. Veuillez noter que la taille d'un Py_UNICODE dépend des options de compilation (soit 16, soit 32 bits). La chaîne de caractères Python ne doit pas contenir de code NULL. Si elle en contient, une exception ValueError est levée.

Modifié dans la version 3.5: Auparavant, une TypeError était levée quand la chaîne de caractères Python contenait des codes NULL.

Obsolète depuis la version 3.3, sera supprimé dans la version 3.12: Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsWideCharString().

u# (str) [const Py_UNICODE *, Py_ssize_t]

This variant on u stores into two C variables, the first one a pointer to a Unicode data buffer, the second one its length. This variant allows null code points.

Obsolète depuis la version 3.3, sera supprimé dans la version 3.12: Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsWideCharString().

Z (str ou None) [const Py_UNICODE *]

Like u, but the Python object may also be None, in which case the Py_UNICODE pointer is set to NULL.

Obsolète depuis la version 3.3, sera supprimé dans la version 3.12: Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsWideCharString().

Z# (str or None) [const Py_UNICODE *, Py_ssize_t]

Like u#, but the Python object may also be None, in which case the Py_UNICODE pointer is set to NULL.

Obsolète depuis la version 3.3, sera supprimé dans la version 3.12: Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsWideCharString().

U (str) [PyObject *]

Requires that the Python object is a Unicode object, without attempting any conversion. Raises TypeError if the object is not a Unicode object. The C variable may also be declared as PyObject*.

w* (lecture-écriture bytes-like object) [Py_buffer]

This format accepts any object which implements the read-write buffer interface. It fills a Py_buffer structure provided by the caller. The buffer may contain embedded null bytes. The caller have to call PyBuffer_Release() when it is done with the buffer.

es (str) [const char *encoding, char **buffer]

This variant on s is used for encoding Unicode into a character buffer. It only works for encoded data without embedded NUL bytes.

This format requires two arguments. The first is only used as input, and must be a const char* which points to the name of an encoding as a NUL-terminated string, or NULL, in which case 'utf-8' encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a char**; the value of the pointer it references will be set to a buffer with the contents of the argument text. The text will be encoded in the encoding specified by the first argument.

PyArg_ParseTuple() will allocate a buffer of the needed size, copy the encoded data into this buffer and adjust *buffer to reference the newly allocated storage. The caller is responsible for calling PyMem_Free() to free the allocated buffer after use.

et (str, bytes or bytearray) [const char *encoding, char **buffer]

Same as es except that byte string objects are passed through without recoding them. Instead, the implementation assumes that the byte string object uses the encoding passed in as parameter.

es# (str) [const char *encoding, char **buffer, Py_ssize_t *buffer_length]

This variant on s# is used for encoding Unicode into a character buffer. Unlike the es format, this variant allows input data which contains NUL characters.

It requires three arguments. The first is only used as input, and must be a const char* which points to the name of an encoding as a NUL-terminated string, or NULL, in which case 'utf-8' encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a char**; the value of the pointer it references will be set to a buffer with the contents of the argument text. The text will be encoded in the encoding specified by the first argument. The third argument must be a pointer to an integer; the referenced integer will be set to the number of bytes in the output buffer.

Il existe deux modes de fonctionnement :

If *buffer points a NULL pointer, the function will allocate a buffer of the needed size, copy the encoded data into this buffer and set *buffer to reference the newly allocated storage. The caller is responsible for calling PyMem_Free() to free the allocated buffer after usage.

If *buffer points to a non-NULL pointer (an already allocated buffer), PyArg_ParseTuple() will use this location as the buffer and interpret the initial value of *buffer_length as the buffer size. It will then copy the encoded data into the buffer and NUL-terminate it. If the buffer is not large enough, a ValueError will be set.

Dans les deux cas, *buffer_length est la longueur des données encodées, sans l'octet NUL de fin.

et# (str, bytes or bytearray) [const char *encoding, char **buffer, Py_ssize_t *buffer_length]

Same as es# except that byte string objects are passed through without recoding them. Instead, the implementation assumes that the byte string object uses the encoding passed in as parameter.

Les nombres¶

b (int) [unsigned char]: Convert a nonnegative Python integer to an unsigned tiny int, stored in a C unsigned char.
B (int) [unsigned char]: Convert a Python integer to a tiny int without overflow checking, stored in a C unsigned char.
h (int) [short int]: Convert a Python integer to a C short int.
H (int) [unsigned short int]: Convert a Python integer to a C unsigned short int, without overflow checking.
i (int) [int]: Convert a Python integer to a plain C int.
I (int) [unsigned int]: Convert a Python integer to a C unsigned int, without overflow checking.
l (int) [long int]: Convert a Python integer to a C long int.
k (int) [unsigned long]: Convert a Python integer to a C unsigned long without overflow checking.
L (int) [long long]: Convert a Python integer to a C long long.
K (int) [unsigned long long]: Convert a Python integer to a C unsigned long long without overflow checking.
n (int) [Py_ssize_t]: Convertit un entier Python en un Py_ssize_t.
c (bytes ou bytearray de longueur 1) [char]: Convert a Python byte, represented as a bytes or bytearray object of length 1, to a C char.

Modifié dans la version 3.3: Allow bytearray objects.
C (str de longueur 1) [int]: Convert a Python character, represented as a str object of length 1, to a C int.
f (float) [float]: Convert a Python floating point number to a C float.
d (float) [double]: Convert a Python floating point number to a C double.
D (complex) [Py_complex]: Convertit un nombre complexe Python vers une structure Py_complex C.

Autres objets¶

O (objet) [PyObject *]: Store a Python object (without any conversion) in a C object pointer. The C program thus receives the actual object that was passed. A new strong reference to the object is not created (i.e. its reference count is not increased). The pointer stored is not NULL.
O! (objet) [typeobject, PyObject *]: Store a Python object in a C object pointer. This is similar to O, but takes two C arguments: the first is the address of a Python type object, the second is the address of the C variable (of type PyObject*) into which the object pointer is stored. If the Python object does not have the required type, TypeError is raised.

O& (objet) [converter, anything]

Convert a Python object to a C variable through a converter function. This takes two arguments: the first is a function, the second is the address of a C variable (of arbitrary type), converted to void*. The converter function in turn is called as follows:

status = converter(object, address);

where object is the Python object to be converted and address is the void* argument that was passed to the PyArg_Parse* function. The returned status should be 1 for a successful conversion and 0 if the conversion has failed. When the conversion fails, the converter function should raise an exception and leave the content of address unmodified.

If the converter returns Py_CLEANUP_SUPPORTED, it may get called a second time if the argument parsing eventually fails, giving the converter a chance to release any memory that it had already allocated. In this second call, the object parameter will be NULL; address will have the same value as in the original call.

Modifié dans la version 3.1: Py_CLEANUP_SUPPORTED à été ajouté.

p (bool) [int]

Tests the value passed in for truth (a boolean predicate) and converts the result to its equivalent C true/false integer value. Sets the int to 1 if the expression was true and 0 if it was false. This accepts any valid Python value. See Valeurs booléennes for more information about how Python tests values for truth.

Nouveau dans la version 3.3.

(items) (tuple) [matching-items]

L'objet doit être une séquence Python dont la longueur est le nombre d'unités de formats dans articles. Les arguments C doivent correspondre à chaque unité de format particulière dans articles. Les unités de formats pour les séquences peuvent être imbriquées.

It is possible to pass "long" integers (integers whose value exceeds the platform's LONG_MAX) however no proper range checking is done --- the most significant bits are silently truncated when the receiving field is too small to receive the value (actually, the semantics are inherited from downcasts in C --- your mileage may vary).

Quelques autres caractères ont un sens dans une chaîne de format. On ne doit pas les trouvées dans des parenthèses imbriquées. Ce sont :

|: Indicates that the remaining arguments in the Python argument list are optional. The C variables corresponding to optional arguments should be initialized to their default value --- when an optional argument is not specified, PyArg_ParseTuple() does not touch the contents of the corresponding C variable(s).
$: PyArg_ParseTupleAndKeywords() only: Indicates that the remaining arguments in the Python argument list are keyword-only. Currently, all keyword-only arguments must also be optional arguments, so | must always be specified before $ in the format string.

Nouveau dans la version 3.3.
:: The list of format units ends here; the string after the colon is used as the function name in error messages (the "associated value" of the exception that PyArg_ParseTuple() raises).
;: La liste des unités de format s'arrête ici ; la chaîne après le point-virgule est utilise comme message d'erreur au lieu du message d'erreur par défaut. : et ; sont mutuellement exclusifs.

Note that any Python object references which are provided to the caller are borrowed references; do not release them (i.e. do not decrement their reference count)!

Les arguments additionnels qui sont donnés à ces fonctions doivent être des adresses de variables dont le type est déterminé par la chaîne de format. Elles sont utilisées pour stocker les valeurs du n-uplet d'entrée. Il y a quelques cas, comme décrit précédemment dans le liste des unités de formats, où ces paramètres sont utilisés comme valeurs d'entrée. Dans ce cas, ils devraient correspondre à ce qui est spécifié pour l'unité de format correspondante.

For the conversion to succeed, the arg object must match the format and the format must be exhausted. On success, the PyArg_Parse* functions return true, otherwise they return false and raise an appropriate exception. When the PyArg_Parse* functions fail due to conversion failure in one of the format units, the variables at the addresses corresponding to that and the following format units are left untouched.

Fonction de l'API¶

int PyArg_ParseTuple(PyObject *args, const char *format, ...)¶: Part of the Stable ABI.
Parse the parameters of a function that takes only positional parameters into local variables. Returns true on success; on failure, it returns false and raises the appropriate exception.

int PyArg_VaParse(PyObject *args, const char *format, va_list vargs)¶: Part of the Stable ABI.
Identical to PyArg_ParseTuple(), except that it accepts a va_list rather than a variable number of arguments.

int PyArg_ParseTupleAndKeywords(PyObject *args, PyObject *kw, const char *format, char *keywords[], ...)¶: Part of the Stable ABI.
Parse the parameters of a function that takes both positional and keyword parameters into local variables. The keywords argument is a NULL-terminated array of keyword parameter names. Empty names denote positional-only parameters. Returns true on success; on failure, it returns false and raises the appropriate exception.

Modifié dans la version 3.6: Added support for positional-only parameters.

int PyArg_VaParseTupleAndKeywords(PyObject *args, PyObject *kw, const char *format, char *keywords[], va_list vargs)¶: Part of the Stable ABI.
Identical to PyArg_ParseTupleAndKeywords(), except that it accepts a va_list rather than a variable number of arguments.

int PyArg_ValidateKeywordArguments(PyObject*)¶: Part of the Stable ABI.
Ensure that the keys in the keywords argument dictionary are strings. This is only needed if PyArg_ParseTupleAndKeywords() is not used, since the latter already does this check.

Nouveau dans la version 3.2.

int PyArg_Parse(PyObject *args, const char *format, ...)¶: Part of the Stable ABI.
Function used to deconstruct the argument lists of "old-style" functions --- these are functions which use the METH_OLDARGS parameter parsing method, which has been removed in Python 3. This is not recommended for use in parameter parsing in new code, and most code in the standard interpreter has been modified to no longer use this for that purpose. It does remain a convenient way to decompose other tuples, however, and may continue to be used for that purpose.

int PyArg_UnpackTuple(PyObject *args, const char *name, Py_ssize_t min, Py_ssize_t max, ...)¶

Part of the Stable ABI.

A simpler form of parameter retrieval which does not use a format string to specify the types of the arguments. Functions which use this method to retrieve their parameters should be declared as METH_VARARGS in function or method tables. The tuple containing the actual parameters should be passed as args; it must actually be a tuple. The length of the tuple must be at least min and no more than max; min and max may be equal. Additional arguments must be passed to the function, each of which should be a pointer to a PyObject* variable; these will be filled in with the values from args; they will contain borrowed references. The variables which correspond to optional parameters not given by args will not be filled in; these should be initialized by the caller. This function returns true on success and false if args is not a tuple or contains the wrong number of elements; an exception will be set if there was a failure.

This is an example of the use of this function, taken from the sources for the _weakref helper module for weak references:

static PyObject *
weakref_ref(PyObject *self, PyObject *args)
{
    PyObject *object;
    PyObject *callback = NULL;
    PyObject *result = NULL;

    if (PyArg_UnpackTuple(args, "ref", 1, 2, &object, &callback)) {
        result = PyWeakref_NewRef(object, callback);
    }
    return result;
}

The call to PyArg_UnpackTuple() in this example is entirely equivalent to this call to PyArg_ParseTuple():

PyArg_ParseTuple(args, "O|O:ref", &object, &callback)

Construction des valeurs¶

PyObject *Py_BuildValue(const char *format, ...)¶

Valeur de retour : nouvelle référence. Part of the Stable ABI.

Create a new value based on a format string similar to those accepted by the PyArg_Parse* family of functions and a sequence of values. Returns the value or NULL in the case of an error; an exception will be raised if NULL is returned.

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.

When memory buffers are passed as parameters to supply data to build objects, as for the s and s# formats, the required data is copied. Buffers provided by the caller are never referenced by the objects created by Py_BuildValue(). In other words, if your code invokes malloc() and passes the allocated memory to Py_BuildValue(), your code is responsible for calling free() for that memory once Py_BuildValue() returns.

In the following description, the quoted form is the format unit; the entry in (round) parentheses is the Python object type that the format unit will return; and the entry in [square] brackets is the type of the C value(s) to be passed.

The characters space, tab, colon and comma are ignored in format strings (but not within format units such as s#). This can be used to make long format strings a tad more readable.

s (str ou None) [const char *]: Convert a null-terminated C string to a Python str object using 'utf-8' encoding. If the C string pointer is NULL, None is used.
s# (str or None) [const char *, Py_ssize_t]: Convert a C string and its length to a Python str object using 'utf-8' encoding. If the C string pointer is NULL, the length is ignored and None is returned.
y (bytes) [const char *]: This converts a C string to a Python bytes object. If the C string pointer is NULL, None is returned.
y# (bytes) [const char *, Py_ssize_t]: This converts a C string and its lengths to a Python object. If the C string pointer is NULL, None is returned.
z (str ou None) [const char *]: Same as s.
z# (str or None) [const char *, Py_ssize_t]: Same as s#.
u (str) [const wchar_t *]: Convert a null-terminated wchar_t buffer of Unicode (UTF-16 or UCS-4) data to a Python Unicode object. If the Unicode buffer pointer is NULL, None is returned.
u# (str) [const wchar_t *, Py_ssize_t]: Convert a Unicode (UTF-16 or UCS-4) data buffer and its length to a Python Unicode object. If the Unicode buffer pointer is NULL, the length is ignored and None is returned.
U (str ou None) [const char *]: Same as s.
U# (str or None) [const char *, Py_ssize_t]: Same as s#.
i (int) [int]: Convert a plain C int to a Python integer object.
b (int) [char]: Convert a plain C char to a Python integer object.
h (int) [short int]: Convert a plain C short int to a Python integer object.
l (int) [long int]: Convert a C long int to a Python integer object.
B (int) [unsigned char]: Convert a C unsigned char to a Python integer object.
H (int) [unsigned short int]: Convert a C unsigned short int to a Python integer object.
I (int) [unsigned int]: Convert a C unsigned int to a Python integer object.
k (int) [unsigned long]: Convert a C unsigned long to a Python integer object.
L (int) [long long]: Convert a C long long to a Python integer object.
K (int) [unsigned long long]: Convert a C unsigned long long to a Python integer object.
n (int) [Py_ssize_t]: Convert a C Py_ssize_t to a Python integer.
c (bytes de taille 1) [char]: Convert a C int representing a byte to a Python bytes object of length 1.
C (str de longueur 1) [int]: Convert a C int representing a character to Python str object of length 1.
d (float) [double]: Convert a C double to a Python floating point number.
f (float) [float]: Convert a C float to a Python floating point number.
D (complex) [Py_complex *]: Convert a C Py_complex structure to a Python complex number.
O (objet) [PyObject *]: Pass a Python object untouched but create a new strong reference to it (i.e. its reference count is incremented by one). If the object passed in is a NULL pointer, it is assumed that this was caused because the call producing the argument found an error and set an exception. Therefore, Py_BuildValue() will return NULL but won't raise an exception. If no exception has been raised yet, SystemError is set.
S (objet) [PyObject *]: Same as O.
N (objet) [PyObject *]: Same as O, except it doesn't create a new strong reference. Useful when the object is created by a call to an object constructor in the argument list.
O& (objet) [converter, anything]: Convert anything to a Python object through a converter function. The function is called with anything (which should be compatible with void*) as its argument and should return a "new" Python object, or NULL if an error occurred.
(items) (tuple) [matching-items]: Convert a sequence of C values to a Python tuple with the same number of items.
[items] (list) [matching-items]: Convert a sequence of C values to a Python list with the same number of items.
{items} (dict) [matching-items]: Convert a sequence of C values to a Python dictionary. Each pair of consecutive C values adds one item to the dictionary, serving as key and value, respectively.

If there is an error in the format string, the SystemError exception is set and NULL returned.

PyObject *Py_VaBuildValue(const char *format, va_list vargs)¶: Valeur de retour : nouvelle référence. Part of the Stable ABI.
Identical to Py_BuildValue(), except that it accepts a va_list rather than a variable number of arguments.

Analyse des arguments et construction des valeurs¶