The Py_BuildValue() Function
1.9 The Py_BuildValue() Function
This function is the counterpart to PyArg_ParseTuple(). It is declared as follows:
这个函数与函数PyArg_ParseTuple()配对。函数声明如下：
PyObject *Py_BuildValue(char *format, ...);
It recognizes a set of format units similar to the ones recognized by PyArg_ParseTuple(), but the arguments (which are input to the function, not
它与函数PyArg_ParseTuple()都可以识别相同的格式单元集，但是参数（输入而非输出函数）
output) must not be pointers, just values. It returns a new Python object, suitable for returning from a C function called from Python.
不能是指针，只能是数值。它返回一个新的Python对象，适合从Python调用C函数中返回。
One difference with PyArg_ParseTuple(): while the latter requires its first argument to be a tuple (since Python argument lists are always
与PyArg_ParseTuple()不同的是：后者要求它的第一个参数为元组（因为Python的参数列表在内部总是表现为元组），
represented as tuples internally), Py_BuildValue() does not always build a tuple. It builds a tuple only if its format string contains two or more
如果格式字符串为空，它返回None；如果只包含一个格式单元，则它返回由格式单元描述类型相一致的对象。
format unit. To force it to return a tuple of size 0 or one, parenthesize the format string.
要强制返回大小为0或1的元组，则给给格式字符串加上括号。
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
下面的描述，引号内的是格式单元；圆括号内的是格式单元将要返回的Python对象类型；
will return; and the entry in [square] brackets is the type of the C value(s) to be passed.
方括号内的是传递给函数的C的数值类型。
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
格式字符串中的空格，制表符，冒号和逗号将被忽略（在类似"s#"格式单元中的除外）。使用这些字符可以增强格式字符串的可读性。
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 is returned.
- "s#" (string) [char *, int]
- Convert a C string and its length to a Python object. If the C string pointer is NULL, the length is ignored and None is returned.
- "z" (string or None) [char *]
- Same as "s".
- "z#" (string or None) [char *, int]
- Same as "s#".
- "i" (integer) [int]
- Convert a plain C int to a Python integer object.
- "b" (integer) [char]
- Same as "i".
- "h" (integer) [short int]
- Same as "i".
- "l" (integer) [long int]
- Convert a C long int to a Python integer object.
- "c" (string of length 1) [char]
- Convert a C int representing a character to a Python string of length 1.
- "d" (float) [double]
- Convert a C double to a Python floating point number.
- "f" (float) [float]
- Same as "d".
- "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() will return NULL but won't raise an exception. If no exception has been raised yet, PyExc_SystemError is set.
- "S" (object) [PyObject *]
- Same as "O".
- "N" (object) [PyObject *]
- Same as "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]
- 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}" (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.
If there is an error in the format string, the PyExc_SystemError exception is raised and NULL returned.
Examples (to the left the call, to the right the resulting Python value):
Py_BuildValue("") None
Py_BuildValue("i", 123) 123
Py_BuildValue("iii", 123, 456, 789) (123, 456, 789)
Py_BuildValue("s", "hello") 'hello'
Py_BuildValue("ss", "hello", "world") ('hello', 'world')
Py_BuildValue("s#", "hello", 4) 'hell'
Py_BuildValue("()") ()
Py_BuildValue("(i)", 123) (123,)
Py_BuildValue("(ii)", 123, 456) (123, 456)
Py_BuildValue("(i,i)", 123, 456) (123, 456)
Py_BuildValue("[i,i]", 123, 456) [123, 456]
Py_BuildValue("{s:i,s:i}",
"abc", 123, "def", 456) {'abc': 123, 'def': 456}
Py_BuildValue("((ii)(ii)) (ii)",
1, 2, 3, 4, 5, 6) (((1, 2), (3, 4)), (5, 6))
