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+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/c-api/buffer.rst	Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,119 @@
+.. highlightlang:: c
+
+.. _bufferobjects:
+
+Buffer Objects
+--------------
+
+.. sectionauthor:: Greg Stein <gstein@lyra.org>
+
+
+.. index::
+   object: buffer
+   single: buffer interface
+
+Python objects implemented in C can export a group of functions called the
+"buffer interface."  These functions can be used by an object to expose its data
+in a raw, byte-oriented format. Clients of the object can use the buffer
+interface to access the object data directly, without needing to copy it first.
+
+Two examples of objects that support the buffer interface are strings and
+arrays. The string object exposes the character contents in the buffer
+interface's byte-oriented form. An array can also expose its contents, but it
+should be noted that array elements may be multi-byte values.
+
+An example user of the buffer interface is the file object's :meth:`write`
+method. Any object that can export a series of bytes through the buffer
+interface can be written to a file. There are a number of format codes to
+:cfunc:`PyArg_ParseTuple` that operate against an object's buffer interface,
+returning data from the target object.
+
+.. index:: single: PyBufferProcs
+
+More information on the buffer interface is provided in the section 
+:ref:`buffer-structs`, under the description for :ctype:`PyBufferProcs`.
+
+A "buffer object" is defined in the :file:`bufferobject.h` header (included by
+:file:`Python.h`). These objects look very similar to string objects at the
+Python programming level: they support slicing, indexing, concatenation, and
+some other standard string operations. However, their data can come from one of
+two sources: from a block of memory, or from another object which exports the
+buffer interface.
+
+Buffer objects are useful as a way to expose the data from another object's
+buffer interface to the Python programmer. They can also be used as a zero-copy
+slicing mechanism. Using their ability to reference a block of memory, it is
+possible to expose any data to the Python programmer quite easily. The memory
+could be a large, constant array in a C extension, it could be a raw block of
+memory for manipulation before passing to an operating system library, or it
+could be used to pass around structured data in its native, in-memory format.
+
+
+.. ctype:: PyBufferObject
+
+   This subtype of :ctype:`PyObject` represents a buffer object.
+
+
+.. cvar:: PyTypeObject PyBuffer_Type
+
+   .. index:: single: BufferType (in module types)
+
+   The instance of :ctype:`PyTypeObject` which represents the Python buffer type;
+   it is the same object as ``buffer`` and  ``types.BufferType`` in the Python
+   layer. .
+
+
+.. cvar:: int Py_END_OF_BUFFER
+
+   This constant may be passed as the *size* parameter to
+   :cfunc:`PyBuffer_FromObject` or :cfunc:`PyBuffer_FromReadWriteObject`.  It
+   indicates that the new :ctype:`PyBufferObject` should refer to *base* object
+   from the specified *offset* to the end of its exported buffer.  Using this
+   enables the caller to avoid querying the *base* object for its length.
+
+
+.. cfunction:: int PyBuffer_Check(PyObject *p)
+
+   Return true if the argument has type :cdata:`PyBuffer_Type`.
+
+
+.. cfunction:: PyObject* PyBuffer_FromObject(PyObject *base, Py_ssize_t offset, Py_ssize_t size)
+
+   Return a new read-only buffer object.  This raises :exc:`TypeError` if *base*
+   doesn't support the read-only buffer protocol or doesn't provide exactly one
+   buffer segment, or it raises :exc:`ValueError` if *offset* is less than zero.
+   The buffer will hold a reference to the *base* object, and the buffer's contents
+   will refer to the *base* object's buffer interface, starting as position
+   *offset* and extending for *size* bytes. If *size* is :const:`Py_END_OF_BUFFER`,
+   then the new buffer's contents extend to the length of the *base* object's
+   exported buffer data.
+
+
+.. cfunction:: PyObject* PyBuffer_FromReadWriteObject(PyObject *base, Py_ssize_t offset, Py_ssize_t size)
+
+   Return a new writable buffer object.  Parameters and exceptions are similar to
+   those for :cfunc:`PyBuffer_FromObject`.  If the *base* object does not export
+   the writeable buffer protocol, then :exc:`TypeError` is raised.
+
+
+.. cfunction:: PyObject* PyBuffer_FromMemory(void *ptr, Py_ssize_t size)
+
+   Return a new read-only buffer object that reads from a specified location in
+   memory, with a specified size.  The caller is responsible for ensuring that the
+   memory buffer, passed in as *ptr*, is not deallocated while the returned buffer
+   object exists.  Raises :exc:`ValueError` if *size* is less than zero.  Note that
+   :const:`Py_END_OF_BUFFER` may *not* be passed for the *size* parameter;
+   :exc:`ValueError` will be raised in that case.
+
+
+.. cfunction:: PyObject* PyBuffer_FromReadWriteMemory(void *ptr, Py_ssize_t size)
+
+   Similar to :cfunc:`PyBuffer_FromMemory`, but the returned buffer is writable.
+
+
+.. cfunction:: PyObject* PyBuffer_New(Py_ssize_t size)
+
+   Return a new writable buffer object that maintains its own memory buffer of
+   *size* bytes.  :exc:`ValueError` is returned if *size* is not zero or positive.
+   Note that the memory buffer (as returned by :cfunc:`PyObject_AsWriteBuffer`) is
+   not specifically aligned.