bytes 对象
**********

当期望带一个字节串形参但却带一个非字节串形参被调用时，这些函数会引发
"TypeError"。

PyBytesObject

   这种 "PyObject" 的子类型表示一个 Python 字节对象。

PyTypeObject PyBytes_Type

   "PyTypeObject" 的实例代表一个 Python 字节类型，在 Python 层面它与
   "bytes" 是相同的对象。

int PyBytes_Check(PyObject *o)

   如果对象 *o* 是字节对象或字节类型的子类型的实例，则返回 true。

int PyBytes_CheckExact(PyObject *o)

   如果对象 *o* 是字节对象，但不是字节类型子类型的实例，则返回 true。

PyObject* PyBytes_FromString(const char *v)

   Return a new bytes object with a copy of the string *v* as value on
   success, and *NULL* on failure.  The parameter *v* must not be
   *NULL*; it will not be checked.

PyObject* PyBytes_FromStringAndSize(const char *v, Py_ssize_t len)

   Return a new bytes object with a copy of the string *v* as value
   and length *len* on success, and *NULL* on failure.  If *v* is
   *NULL*, the contents of the bytes object are uninitialized.

PyObject* PyBytes_FromFormat(const char *format, ...)

   接受一个 C "printf()" 风格的 *format* 字符串和可变数量的参数，计算
   结果 Python 字节串对象的大小并返回参数值经格式化后的字节串对象。 可
   变数量的参数必须均为 C 类型并且必须恰好与 *format* 字符串中的格式字
   符相对应。 允许使用下列格式字符串:

   +---------------------+-----------------+----------------------------------+
   | 格式字符            | 类型            | 注释                             |
   |=====================|=================|==================================|
   | "%%"                | *不适用*        | 文字%字符。                      |
   +---------------------+-----------------+----------------------------------+
   | "%c"                | int             | 一个字节，被表示为一个 C 语言的  |
   |                     |                 | 整型                             |
   +---------------------+-----------------+----------------------------------+
   | "%d"                | int             | Exactly equivalent to            |
   |                     |                 | "printf("%d")".                  |
   +---------------------+-----------------+----------------------------------+
   | "%u"                | unsigned int    | Exactly equivalent to            |
   |                     |                 | "printf("%u")".                  |
   +---------------------+-----------------+----------------------------------+
   | "%ld"               | 长整型          | Exactly equivalent to            |
   |                     |                 | "printf("%ld")".                 |
   +---------------------+-----------------+----------------------------------+
   | "%lu"               | unsigned long   | Exactly equivalent to            |
   |                     |                 | "printf("%lu")".                 |
   +---------------------+-----------------+----------------------------------+
   | "%zd"               | Py_ssize_t      | Exactly equivalent to            |
   |                     |                 | "printf("%zd")".                 |
   +---------------------+-----------------+----------------------------------+
   | "%zu"               | size_t          | Exactly equivalent to            |
   |                     |                 | "printf("%zu")".                 |
   +---------------------+-----------------+----------------------------------+
   | "%i"                | int             | Exactly equivalent to            |
   |                     |                 | "printf("%i")".                  |
   +---------------------+-----------------+----------------------------------+
   | "%x"                | int             | Exactly equivalent to            |
   |                     |                 | "printf("%x")".                  |
   +---------------------+-----------------+----------------------------------+
   | "%s"                | char*           | 以 null 为终止符的 C 字符数组。  |
   +---------------------+-----------------+----------------------------------+
   | "%p"                | void*           | 一个 C 指针的十六进制表示形式。  |
   |                     |                 | 基本等价于 "printf("%p")" 但它会 |
   |                     |                 | 确 保以字面值 "0x" 开头，不论系  |
   |                     |                 | 统平台上 "printf" 的输出是什么。 |
   +---------------------+-----------------+----------------------------------+

   无法识别的格式字符会导致将格式字符串的其余所有内容原样复制到结果对
   象，并丢弃所有多余的参数。

PyObject* PyBytes_FromFormatV(const char *format, va_list vargs)

   与 "PyBytes_FromFormat()" 完全相同，除了它需要两个参数。

PyObject* PyBytes_FromObject(PyObject *o)

   返回字节表示实现缓冲区协议的对象*o*。

Py_ssize_t PyBytes_Size(PyObject *o)

   返回字节对象*o*中字节的长度。

Py_ssize_t PyBytes_GET_SIZE(PyObject *o)

   宏版本的 "PyBytes_Size()" 但是不带错误检查。

char* PyBytes_AsString(PyObject *o)

   Return a pointer to the contents of *o*.  The pointer refers to the
   internal buffer of *o*, which consists of "len(o) + 1" bytes.  The
   last byte in the buffer is always null, regardless of whether there
   are any other null bytes.  The data must not be modified in any
   way, unless the object was just created using
   "PyBytes_FromStringAndSize(NULL, size)". It must not be
   deallocated.  If *o* is not a bytes object at all,
   "PyBytes_AsString()" returns *NULL* and raises "TypeError".

char* PyBytes_AS_STRING(PyObject *string)

   宏版本的 "PyBytes_AsString()" 但是不带错误检测。

int PyBytes_AsStringAndSize(PyObject *obj, char **buffer, Py_ssize_t *length)

   通过输出变量 *buffer* 和 *length* 返回以 null 为终止符的对象 *obj*
   的内容。

   If *length* is *NULL*, the bytes object may not contain embedded
   null bytes; if it does, the function returns "-1" and a
   "ValueError" is raised.

   该缓冲区指向 *obj* 的内部缓冲，它的末尾包含一个额外的空字节（不算在
   *length* 当中）。 该数据不可通过任何方式来修改，除非是刚使用
   "PyBytes_FromStringAndSize(NULL, size)" 创建该对象。 它不可被撤销分
   配。 如果 *obj* 根本不是一个字节串对象，则
   "PyBytes_AsStringAndSize()" 将返回 "-1" 并引发 "TypeError"。

   3.5 版更變: 以前，当字节串对象中出现嵌入的空字节时将引发
   "TypeError"。

void PyBytes_Concat(PyObject **bytes, PyObject *newpart)

   Create a new bytes object in **bytes* containing the contents of
   *newpart* appended to *bytes*; the caller will own the new
   reference.  The reference to the old value of *bytes* will be
   stolen.  If the new object cannot be created, the old reference to
   *bytes* will still be discarded and the value of **bytes* will be
   set to *NULL*; the appropriate exception will be set.

void PyBytes_ConcatAndDel(PyObject **bytes, PyObject *newpart)

   在 **bytes* 中创建新的字节串对象，其中包含添加到 *bytes* 的
   *newpart* 的内容。 此版本会减少 *newpart* 的引用计数。

int _PyBytes_Resize(PyObject **bytes, Py_ssize_t newsize)

   A way to resize a bytes object even though it is "immutable". Only
   use this to build up a brand new bytes object; don't use this if
   the bytes may already be known in other parts of the code.  It is
   an error to call this function if the refcount on the input bytes
   object is not one. Pass the address of an existing bytes object as
   an lvalue (it may be written into), and the new size desired.  On
   success, **bytes* holds the resized bytes object and "0" is
   returned; the address in **bytes* may differ from its input value.
   If the reallocation fails, the original bytes object at **bytes* is
   deallocated, **bytes* is set to *NULL*, "MemoryError" is set, and
   "-1" is returned.
