这些函数在创建自己的扩展函数和方法时很有用。额外信息和范例可用于 扩展和嵌入 Python 解释器 .
描述这些函数中的前 3，
PyArg_ParseTuple()
,
PyArg_ParseTupleAndKeywords()
，和
PyArg_Parse()
，全部使用
格式字符串
用于告诉函数有关期望自变量。格式字符串使用相同句法，对于这些函数中的每个而言。
A format string consists of zero or more “format units.” A format unit describes one Python object; it is usually a single character or a parenthesized sequence of format units. With a few exceptions, a format unit that is not a parenthesized sequence normally corresponds to a single address argument to these functions. In the following description, the quoted form is the format unit; the entry in (round) parentheses is the Python object type that matches the format unit; and the entry in [square] brackets is the type of the C variable(s) whose address should be passed.
These formats allow accessing an object as a contiguous chunk of memory. You don’t have to provide raw storage for the returned unicode or bytes area. Also, you won’t have to release any memory yourself, except with the
es
,
es#
,
et
and
et#
formats.
s
(string or Unicode) [const char *]
Convert a Python string or Unicode object to a C pointer to a character string. You must not provide storage for the string itself; a pointer to an existing string is stored into the character pointer variable whose address you pass. The C string is NUL-terminated. The Python string must not contain embedded NUL bytes; if it does, a
TypeError
exception is raised. Unicode objects are converted to C strings using the default encoding. If this conversion fails, a
UnicodeError
被引发。
s#
(string, Unicode or any read buffer compatible object) [const char *, int (or
Py_ssize_t
, see below)]
This variant on
s
stores into two C variables, the first one a pointer to a character string, the second one its length. In this case the Python string may contain embedded null bytes. Unicode objects pass back a pointer to the default encoded string version of the object if such a conversion is possible. All other read-buffer compatible objects pass back a reference to the raw internal data representation.
Starting with Python 2.5 the type of the length argument can be controlled by defining the macro
PY_SSIZE_T_CLEAN
先于包括
Python.h
. If the macro is defined, length is a
Py_ssize_t
rather than an int.
s*
(string, Unicode, or any buffer compatible object) [Py_buffer]
类似于
s#
, this code fills a Py_buffer structure provided by the caller. The buffer gets locked, so that the caller can subsequently use the buffer even inside a
Py_BEGIN_ALLOW_THREADS
block; the caller is responsible for calling
PyBuffer_Release
with the structure after it has processed the data.
2.6 版新增。
z
(string, Unicode or
None
) [const char *]
像
s
, but the Python object may also be
None
, in which case the C pointer is set to
NULL
.
z#
(string, Unicode,
None
or any read buffer compatible object) [const char *, int]
This is to
s#
as
z
is to
s
.
z*
(string, Unicode,
None
or any buffer compatible object) [Py_buffer]
This is to
s*
as
z
is to
s
.
2.6 版新增。
u
(Unicode) [Py_UNICODE *]
Convert a Python Unicode object to a C pointer to a NUL-terminated buffer of 16-bit Unicode (UTF-16) data. As with
s
, there is no need to provide storage for the Unicode data buffer; a pointer to the existing Unicode data is stored into the
Py_UNICODE
pointer variable whose address you pass.
u#
(Unicode) [Py_UNICODE *, int]
This variant on
u
stores into two C variables, the first one a pointer to a Unicode data buffer, the second one its length. Non-Unicode objects are handled by interpreting their read-buffer pointer as pointer to a
Py_UNICODE
array.
es
(string, Unicode or character buffer compatible object) [const char *encoding, char **buffer]
This variant on
s
is used for encoding Unicode and objects convertible to 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 the default 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
(string, Unicode or character buffer compatible object) [const char *encoding, char **buffer]
如同
es
except that 8-bit string objects are passed through without recoding them. Instead, the implementation assumes that the string object uses the encoding passed in as parameter.
es#
(string, Unicode or character buffer compatible object) [const char *encoding, char **buffer, int *buffer_length]
This variant on
s#
is used for encoding Unicode and objects convertible to 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 the default 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.
There are two modes of operation:
若
*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.
若
*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
TypeError
will be set. Note: starting from Python 3.6 a
ValueError
will be set.
In both cases, *buffer_length is set to the length of the encoded data without the trailing NUL byte.
et#
(string, Unicode or character buffer compatible object) [const char *encoding, char **buffer, int *buffer_length]
如同
es#
except that string objects are passed through without recoding them. Instead, the implementation assumes that the string object uses the encoding passed in as parameter.
b
(integer) [unsigned char]
Convert a nonnegative Python integer to an unsigned tiny int, stored in a C
unsigned char
.
B
(integer) [unsigned char]
Convert a Python integer to a tiny int without overflow checking, stored in a C
unsigned char
.
2.3 版新增。
h
(integer) [short int]
将 Python 整数转换为 C
short int
.
H
(integer) [unsigned short int]
将 Python 整数转换为 C
unsigned short int
，没有溢出校验。
2.3 版新增。
i
(integer) [int]
将 Python 整数转换为纯 C
int
.
I
(integer) [unsigned int]
将 Python 整数转换为 C
unsigned int
，没有溢出校验。
2.3 版新增。
l
(integer) [long int]
将 Python 整数转换为 C
long int
.
k
(integer) [unsigned long]
Convert a Python integer or long integer to a C
unsigned long
没有溢出校验。
2.3 版新增。
L
(integer) [PY_LONG_LONG]
将 Python 整数转换为 C
long long
. This format is only available on platforms that support
long long
(或
_int64
在 Windows)。
K
(integer) [unsigned PY_LONG_LONG]
Convert a Python integer or long integer to a C
unsigned long long
without overflow checking. This format is only available on platforms that support
unsigned long long
(或
unsigned _int64
在 Windows)。
2.3 版新增。
n
(integer) [Py_ssize_t]
Convert a Python integer or long integer to a C
Py_ssize_t
.
2.5 版新增。
c
(string of length 1) [char]
Convert a Python character, represented as a string of length 1, to a C
char
.
f
(float) [float]
将 Python 浮点数转换为 C
float
.
d
(float) [double]
将 Python 浮点数转换为 C
double
.
D
(complex) [Py_complex]
将 Python 复数转换为 C
Py_complex
结构。
O
(object) [PyObject *]
将 Python 对象 (无需任何转换) 存储在 C 对象指针中。因此，C 程序接收实际传递对象。不会递增对象的引用计数。存储指针不是 NULL .
O!
(object) [
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
被引发。
O&
(object) [
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 *
。
converter
function in turn is called as follows:
status = converter(object, address);
where
object
is the Python object to be converted and
address
是
void*
argument that was passed to the
PyArg_Parse*()
function. The returned
status
应该为
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
未经修改。
S
(string) [PyStringObject *]
像
O
but requires that the Python object is a string object. Raises
TypeError
if the object is not a string object. The C variable may also be declared as
PyObject*
.
U
(Unicode string) [PyUnicodeObject *]
像
O
but requires that the Python object is a Unicode object. Raises
TypeError
if the object is not a Unicode object. The C variable may also be declared as
PyObject*
.
t#
(read-only character buffer) [char *, int]
像
s#
, but accepts any object which implements the read-only buffer interface. The
char*
variable is set to point to the first byte of the buffer, and the
int
is set to the length of the buffer. Only single-segment buffer objects are accepted;
TypeError
is raised for all others.
w
(read-write character buffer) [char *]
类似于
s
, but accepts any object which implements the read-write buffer interface. The caller must determine the length of the buffer by other means, or use
w#
instead. Only single-segment buffer objects are accepted;
TypeError
is raised for all others.
w#
(read-write character buffer) [char *, Py_ssize_t]
像
s#
, but accepts any object which implements the read-write buffer interface. The
char *
variable is set to point to the first byte of the buffer, and the
Py_ssize_t
is set to the length of the buffer. Only single-segment buffer objects are accepted;
TypeError
is raised for all others.
w*
(read-write byte-oriented buffer) [Py_buffer]
This is to
w
what
s*
is to
s
.
2.6 版新增。
(items)
(tuple) [
matching-items
]
The object must be a Python sequence whose length is the number of format units in 项 . The C arguments must correspond to the individual format units in 项 . Format units for sequences may be nested.
注意
Prior to Python version 1.5.2, this format specifier only accepted a tuple containing the individual parameters, not an arbitrary sequence. Code which previously caused
TypeError
to be raised here may now proceed without an exception. This is not expected to be a problem for existing code.
It is possible to pass Python long integers where integers are requested; 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).
A few other characters have a meaning in a format string. These may not occur inside nested parentheses. They are:
|
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).
:
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).
;
The list of format units ends here; the string after the semicolon is used as the error message
代替
of the default error message.
:
and
;
mutually exclude each other.
Note that any Python object references which are provided to the caller are borrowed references; do not decrement their reference count!
Additional arguments passed to these functions must be addresses of variables whose type is determined by the format string; these are used to store values from the input tuple. There are a few cases, as described in the list of format units above, where these parameters are used as input values; they should match what is specified for the corresponding format unit in that case.
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.
PyArg_ParseTuple
(
PyObject
*args
, const char
*format
, ...
)
¶
仅将函数的位置参数，剖析成局部变量。返回 True 当成功时；当故障时，它返回 False 并引发适当异常。
PyArg_VaParse
(
PyObject
*args
, const char
*format
, va_list
vargs
)
¶
等同于
PyArg_ParseTuple()
，除了它接受 va_list 而不是可变数自变量。
PyArg_ParseTupleAndKeywords
(
PyObject
*args
,
PyObject
*kw
, const char
*format
, char
*keywords[]
, ...
)
¶
Parse the parameters of a function that takes both positional and keyword parameters into local variables. Returns true on success; on failure, it returns false and raises the appropriate exception.
PyArg_VaParseTupleAndKeywords
(
PyObject
*args
,
PyObject
*kw
, const char
*format
, char
*keywords[]
, va_list
vargs
)
¶
等同于
PyArg_ParseTupleAndKeywords()
，除了它接受 va_list 而不是可变数自变量。
PyArg_Parse
(
PyObject
*args
, const char
*format
, ...
)
¶
Function used to deconstruct the argument lists of “old-style” functions — these are functions which use the
METH_OLDARGS
parameter parsing method. 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.
PyArg_UnpackTuple
(
PyObject
*args
, const char
*name
, Py_ssize_t
min
, Py_ssize_t
max
, ...
)
¶
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; }
调用
PyArg_UnpackTuple()
in this example is entirely equivalent to this call to
PyArg_ParseTuple()
:
PyArg_ParseTuple(args, "O|O:ref", &object, &callback)
2.2 版新增。
Changed in version 2.5:
This function used an
int
type for
min
and
max
. This might require changes in your code for properly supporting 64-bit systems.
Py_BuildValue
(
const char
*format
, ...
)
¶
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
被返回。
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()
返回。
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
(string) [char *]
Convert a null-terminated C string to a Python object. If the C string pointer is
NULL
,
None
被使用。
s#
(string) [char *, int]
Convert a C string and its length to a Python object. If the C string pointer is
NULL
，长度被忽略和
None
被返回。
z
(string or
None
) [char *]
如同
s
.
z#
(string or
None
) [char *, int]
如同
s#
.
u
(Unicode string) [Py_UNICODE *]
Convert a null-terminated buffer of Unicode (UCS-2 or UCS-4) data to a Python Unicode object. If the Unicode buffer pointer is
NULL
,
None
被返回。
u#
(Unicode string) [Py_UNICODE *, int]
Convert a Unicode (UCS-2 or UCS-4) data buffer and its length to a Python Unicode object. If the Unicode buffer pointer is
NULL
，长度被忽略和
None
被返回。
i
(integer) [int]
转换纯 C
int
到 Python 整数对象。
b
(integer) [char]
转换纯 C
char
到 Python 整数对象。
h
(integer) [short int]
转换纯 C
short int
到 Python 整数对象。
l
(integer) [long int]
转换 C
long int
到 Python 整数对象。
B
(integer) [unsigned char]
转换 C
unsigned char
到 Python 整数对象。
H
(integer) [unsigned short int]
转换 C
unsigned short int
到 Python 整数对象。
I
(integer/long) [unsigned int]
转换 C
unsigned int
to a Python integer object or a Python long integer object, if it is larger than
sys.maxint
.
k
(integer/long) [unsigned long]
转换 C
unsigned long
to a Python integer object or a Python long integer object, if it is larger than
sys.maxint
.
L
(long) [PY_LONG_LONG]
转换 C
long long
to a Python long integer object. Only available on platforms that support
long long
.
K
(long) [unsigned PY_LONG_LONG]
转换 C
unsigned long long
to a Python long integer object. Only available on platforms that support
unsigned long long
.
n
(int) [Py_ssize_t]
转换 C
Py_ssize_t
to a Python integer or long integer.
2.5 版新增。
c
(string of length 1) [char]
转换 C
int
representing a character to a Python string of length 1.
d
(float) [double]
转换 C
double
到 Python 浮点数。
f
(float) [float]
如同
d
.
D
(complex) [Py_complex *]
转换 C
Py_complex
structure to a Python complex number.
O
(object) [PyObject *]
Pass a Python object untouched (except for its reference count, which 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()
将返回
NULL
but won’t raise an exception. If no exception has been raised yet,
SystemError
有设置。
S
(object) [PyObject *]
如同
O
.
N
(object) [PyObject *]
如同
O
, except it doesn’t increment the reference count on the object. Useful when the object is created by a call to an object constructor in the argument list.
O&
(object) [
converter
,
anything
]
转换
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
若出现错误。
(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}
(dictionary) [
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.
若格式字符串中有错误，
SystemError
异常被设置和
NULL
被返回。
Py_VaBuildValue
(
const char
*format
, va_list
vargs
)
¶
等同于
Py_BuildValue()
，除了它接受 va_list 而不是可变数自变量。