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Travis E. Oliphant 2007-04-26 21:43:28 +00:00
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@ -1,8 +1,9 @@
PEP: 3118
Title: Revising the buffer protocol
Version: $Revision$
Last-Modified: $Date$
Author: Travis Oliphant <oliphant@ee.byu.edu>, Carl Banks <pythondev@aerojockey.com>
Authors: Travis Oliphant <oliphant@ee.byu.edu>, Carl Banks <pythondev@aerojockey.com>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
@ -13,8 +14,8 @@ Abstract
========
This PEP proposes re-designing the buffer interface (PyBufferProcs
function pointers) to improve the way Python allows memory sharing
in Python 3.0
function pointers) to improve the way Python allows memory sharing in
Python 3.0
In particular, it is proposed that the character buffer portion
of the API be elminated and the multiple-segment portion be
@ -73,7 +74,7 @@ has issues:
NumPy uses the notion of constant striding in each dimension as its
basic concept of an array. With this concept, a simple sub-region
of a larger array can be described without copying the data. T
of a larger array can be described without copying the data.
Thus, stride information is the additional information that must be
shared.
@ -151,7 +152,7 @@ Change the PyBufferProcs structure to
::
typedef int (*getbufferproc)(PyObject *obj, struct bufferinfo *view, int flags)
typedef int (*getbufferproc)(PyObject *obj, PyBuffer *view, int flags)
This function returns 0 on success and -1 on failure (and raises an
error). The first variable is the "exporting" object. The second
@ -160,54 +161,137 @@ then no information is returned but a lock on the memory is still
obtained. In this case, the corresponding releasebuffer should also
be called with NULL.
The third argument indicates what kind of buffer the exporter is allowed to return. It tells the
exporter what elements the bufferinfo structure the consumer is going to make use of. This
allows the exporter to simplify and/or raise an error if it can't support the operation.
The third argument indicates what kind of buffer the consumer is
prepared to deal with and therefore what kind of buffer the exporter
is allowed to return. The new buffer interface allows for much more
complicated memory sharing possibilities. Some consumers may not be
able to handle all the complexibity but may want to see if the
exporter will let them take a simpler view to its memory.
It also allows the caller to make a request for a simple "view" and
receive it or have an error raised if it's not possible.
In addition, some exporters may not be able to share memory in every
possible way and may need to raise errors to signal to some consumers
that something is just not possible. These errors should be
PyErr_BufferError unless there is another error that is actually
causing the problem. The exporter can use flags information to
simplify how much of the PyBuffer structure is filled in with
non-default values and/or raise an error if the object can't support a
simpler view of its memory.
All of the following assume that at least buf, len, and readonly will be
utilized by the caller.
The exporter should always fill in all elements of the buffer
structure (with defaults if nothing else is requested).
Py_BUF_SIMPLE
The returned buffer will only be assumed to be readable (the object
may or may not have writeable memory). Only the buf, len, and
readonly variables may be accessed. The format will be
assumed to be unsigned bytes. This is a "stand-alone" flag constant.
It never needs to be \|'d to the others.
Some flags are useful for requesting a specific kind of memory
segment, while others indicate to the exporter what kind of
information the consumer can deal with. If certain information is not
asked for by the consumer, but the exporter cannot share its memory
without that information, then a PyErr_BufferError should be raised.
Py_BUF_WRITEABLE
The returned buffer must be writeable. If it cannot be, then raise an error.
Py_BUF_READONLY
The returned buffer must be readonly and the underlying object should make
its memory readonly if that is possible.
PyBUF_SIMPLE
Py_BUF_FORMAT
The consumer will be using the format string information so make sure that
member is filled correctly.
This is the default flag state (0). The returned buffer may or may
not have writeable memory. The format will be assumed to be
unsigned bytes . This is a "stand-alone" flag constant. It never
needs to be |'d to the others. The exporter will raise an error if
it cannot provide such a contiguous buffer of bytes.
Py_BUF_SHAPE
The consumer can (and might) make use of using the ndims and shape members of the structure
so make sure they are filled in correctly.
PyBUF_REQ_WRITEABLE
The returned buffer must be writeable. If it is not writeable,
then raise an error.
PyBUF_REQ_LOCKDATA
The returned buffer must be readonly. If the object is already
read-only or it can make its memory read-only (and there are no
other views on the object) then it should do so and return the
buffer information. If the object does not have read-only memory
(or cannot make it read-only), then an error should be raised.
PyBUF_REQ_FORMAT
The returned buffer must have true format information if this flag
is provided. This would be used when the consumer is going to be
checking for what 'kind' of data is actually stored. An exporter
should always be able to provide this information if requested. If
format is not explicitly requested then the format must be returned
as NULL (which means "B")
PyBUF_REQ_ALIGNED (implies PyBUF_REQ_FORMAT)
The returned buffer must have all (primitive data-type entries)
aligned as the compiler would align them
PyBUF_ALW_ND
The returned buffer must provide shape information. The memory will
be assumed C-style contiguous (last dimension varies the fastest).
The exporter may raise an error if it cannot provide this kind of
contiguous buffer.
Py_BUF_STRIDES (implies SHAPE)
The consumer can (and might) make use of the strides member of the structure (as well
as ndims and shape)
PyBUF_ALW_STRIDES (implies PyBUF_ALW_ND)
Py_BUF_OFFSETS (implies STRIDES)
The consumer can (and might) make use of the suboffsets member (as well as
ndims, shape, and strides)
The returned buffer must provide strides information. This would be
used when the consumer can handle strided, discontiguous arrays.
Handling strides automatically assumes you can handle shape.
The exporter may raise an error if cannot provide a strided-only
representation of the data (i.e. without the suboffsets).
Thus, the consumer simply wanting an contiguous chunk of bytes from
the object would use Py_BUF_SIMPLE, while a consumer that understands
how to make use of the most complicated cases would use
Py_BUF_OFFSETS.
PyBUF_REQ_C_CONTIGUOUS
PyBUF_REQ_F_CONTIGUOUS
PyBUF_REQ_ANY_CONTIGUOUS
These flags indicate that the returned buffer must be respectively,
C-contiguous (last dimension varies the fastest), Fortran
contiguous (first dimension varies the fastest) or either one.
All of these flags imply PyBUF_ALW_STRIDES and guarantee that the
strides buffer info structure will be filled in correctly.
PyBUF_ALW_INDIRECT (implies PyBUF_ALW_STRIDES)
The returned buffer must have suboffsets information. This would
be used when the consumer can handle indirect array referencing
implied by these suboffsets.
Specialized combinations of flags for specific kinds of memory_sharing.
Multi-dimensional (but contiguous)
PyBUF_CONTIG (PyBUF_ALW_ND | PyBUF_REQ_WRITEABLE | PyBUF_REQ_ALIGNED)
PyBUF_CONTIG_RO (PyBUF_ALW_ND | PyBUF_REQ_ALIGNED)
PyBUF_CONTIG_LCK (PyBUF_ALW_ND | PyBUF_REQ_LOCKDATA | PyBUF_REQ_ALIGNED)
Multi-dimensional using strides but aligned
PyBUF_STRIDED (PyBUF_ALW_STRIDES | PyBUF_REQ_WRITEABLE | PyBUF_REQ_ALIGNED)
PyBUF_STRIDED_RO (PyBUF_ALW_STRIDES | PyBUF_REQ_ALIGNED)
PyBUF_STRIDED_LCK (PyBUF_ALW_STRIDES | PyBUF_REQ_LOCKDATA | PyBUF_REQ_ALIGNED)
Multi-dimensional using strides and not necessarily aligned
PyBUF_RECORDS (PyBUF_ALW_STRIDES | PyBUF_REQ_WRITEABLE | PyBUF_REQ_FORMAT)
PyBUF_RECORDS_RO (PyBUF_ALW_STRIDES | PyBUF_REQ_FORMAT)
PyBUF_RECORDS_LCK (PyBUF_ALW_STRIDES | PyBUF_REQ_LOCKDATA | PyBUF_REQ_FORMAT)
Multi-dimensional using sub-offsets
PyBUF_FULL (PyBUF_ALW_INDIRECT | PyBUF_REQ_WRITEABLE | PyBUF_REQ_FORMAT)
PyBUF_FULL_RO (PyBUF_ALW_INDIRECT | PyBUF_REQ_FORMAT)
PyBUF_FULL_LCK (PyBUF_ALW_INDIRECT | PyBUF_REQ_LOCKDATA | PyBUF_REQ_FORMAT)
Thus, the consumer simply wanting a contiguous chunk of bytes from
the object would use PyBUF_SIMPLE, while a consumer that understands
how to make use of the most complicated cases could use PyBUF_FULL
The format information is only guaranteed to be non-NULL if
PyBUF_REQ_FORMAT is in the flag argument, otherwise it is expected the
consumer will assume unsigned bytes.
There is a C-API that simple exporting objects can use to fill-in the
buffer info structure correctly according to the provided flags if a
contiguous chunk of memory is all that can be exported.
contiguous chunk of "unsigned bytes" is all that can be exported.
The bufferinfo structure is::
@ -216,21 +300,23 @@ The bufferinfo structure is::
void *buf;
Py_ssize_t len;
int readonly;
char *format;
int ndims;
const char *format;
int ndim;
Py_ssize_t *shape;
Py_ssize_t *strides;
Py_ssize_t *suboffsets;
int itemsize;
void *internal;
};
} PyBuffer;
Before calling this function, the bufferinfo structure can be filled with
whatever. Upon return from getbufferproc, the bufferinfo structure is filled in
with relevant information about the buffer. This same bufferinfo
structure must be passed to bf_releasebuffer (if available) when the
consumer is done with the memory. The caller is responsible for
keeping a reference to obj until releasebuffer is called (i.e. this
call does not alter the reference count of obj).
Before calling this function, the bufferinfo structure can be filled
with whatever. Upon return from getbufferproc, the bufferinfo
structure is filled in with relevant information about the buffer.
This same bufferinfo structure must be passed to bf_releasebuffer (if
available) when the consumer is done with the memory. The caller is
responsible for keeping a reference to obj until releasebuffer is
called (i.e. the call to bf_getbuffer does not alter the reference
count of obj).
The members of the bufferinfo structure are:
@ -242,33 +328,39 @@ len
same as the product of the shape array multiplied by the number of
bytes per item of memory.
readonly
an integer variable to hold whether or not the memory is
readonly. 1 means the memory is readonly, zero means the
memory is writeable.
readonly
an integer variable to hold whether or not the memory is readonly.
1 means the memory is readonly, zero means the memory is
writeable, and -1 means the memory was "locked" (changed from
writeable to readonly) when this PyBuffer structure was filled-in
and therefore should be unlocked when this PyBuffer structure is
"released" (this is supported only by some exporters).
format
a NULL-terminated format-string (following the struct-style syntax
including extensions) indicating what is in each element of
memory. The number of elements is len / itemsize, where itemsize
is the number of bytes implied by the format. For standard
unsigned bytes use a format string of "B".
is the number of bytes implied by the format. This can be NULL which
implies standard unsigned bytes ("B").
ndims
a variable storing the number of dimensions the memory represents.
Must be >=0.
Must be >=0. A value of 0 means that shape and strides and suboffsets
must be NULL (i.e. the memory represents a scalar).
shape
an array of ``Py_ssize_t`` of length ``ndims`` indicating the
shape of the memory as an N-D array. Note that ``((*shape)[0] *
... * (*shape)[ndims-1])*itemsize = len``.
... * (*shape)[ndims-1])*itemsize = len``. If ndims is 0 (indicating
a scalar), then this must be NULL.
strides
address of a ``Py_ssize_t*`` variable that will be filled with a
pointer to an array of ``Py_ssize_t`` of length ``*ndims``
indicating the number of bytes to skip to get to the next element
in each dimension. For C-style contiguous arrays (where the
last-dimension varies the fastest) this must be filled in.
pointer to an array of ``Py_ssize_t`` of length ``ndims`` (or NULL
if ndims is 0). indicating the number of bytes to skip to get to
the next element in each dimension. If this is not requested by
the caller (PyBUF_ALW_STRIDES is not set), then this should be set
to NULL which indicates a C-style contiguous array.
suboffsets
address of a ``Py_ssize_t *`` variable that will be filled with a
@ -279,14 +371,14 @@ suboffsets
suboffset value that it negative indicates that no de-referencing
should occur (striding in a contiguous memory block). If all
suboffsets are negative (i.e. no de-referencing is needed, then
this must be NULL.
this must be NULL (the default value).
For clarity, here is a function that returns a pointer to the
element in an N-D array pointed to by an N-dimesional index when
there are both strides and suboffsets.::
there are both non-NULL strides and suboffsets.::
void* get_item_pointer(int ndim, void* buf, Py_ssize_t* strides,
Py_ssize_t* suboffsets, Py_ssize_t *indices) {
Py_ssize_t* suboffsets, Py_ssize_t *indices) {
char* pointer = (char*)buf;
int i;
for (i = 0; i < ndim; i++) {
@ -304,28 +396,36 @@ suboffsets
the location of the starting pointer directly (i.e. buf would
be modified).
itemsize
This is a storage for the itemsize of each element of the shared
memory. It is strictly un-necessary as it can be obtained using
PyBuffer_SizeFromFormat, however an exporter may know this
information without parsing the format string and it is necessary
to know the itemsize for proper interpretation of striding.
Therefore, storing it is more convenient and faster.
internal
This is for use internally by the exporting object. For example,
this might be re-cast as an integer by the exporter and used to
store flags about whether or not the shape, strides, and suboffsets
arrays must be freed when the buffer is released. The consumer
should never touch this value.
should never alter this value.
The exporter is responsible for making sure the memory pointed to by
buf, format, shape, strides, and suboffsets is valid until
The exporter is responsible for making sure that any memory pointed to
by buf, format, shape, strides, and suboffsets is valid until
releasebuffer is called. If the exporter wants to be able to change
shape, strides, and/or suboffsets before releasebuffer is called then
it should allocate those arrays when getbuffer is called (pointing to
them in the buffer-info structure provided) and free them when
releasebuffer is called.
an object's shape, strides, and/or suboffsets before releasebuffer is
called then it should allocate those arrays when getbuffer is called
(pointing to them in the buffer-info structure provided) and free them
when releasebuffer is called.
The same bufferinfo struct should be used in the release-buffer
interface call. The caller is responsible for the memory of the
bufferinfo structure itself.
``typedef int (*releasebufferproc)(PyObject *obj, struct bufferinfo *view)``
``typedef int (*releasebufferproc)(PyObject *obj, PyBuffer *view)``
Callers of getbufferproc must make sure that this function is
called when memory previously acquired from the object is no
longer needed. The exporter of the interface must make sure that
@ -348,7 +448,8 @@ each object.
All that is specifically required by the exporter, however, is to
ensure that any memory shared through the bufferinfo structure remains
valid until releasebuffer is called on the bufferinfo structure.
valid until releasebuffer is called on the bufferinfo structure
exporting that memory.
New C-API calls are proposed
@ -362,69 +463,94 @@ Return 1 if the getbuffer function is available otherwise 0.
::
int PyObject_GetBuffer(PyObject *obj, struct bufferinfo *view, int flags)
int PyObject_GetBuffer(PyObject *obj, PyBuffer *view,
int flags)
This is a C-API version of the getbuffer function call. It checks to
make sure object has the required function pointer and issues the
call. Returns -1 and raises an error on failure and returns 0 on
success.
call. Returns -1 and raises an error on failure and returns 0 on
success.
::
int PyObject_ReleaseBuffer(PyObject *obj, PyBuffer *view)
int PyObject_ReleaseBuffer(PyObject *obj, struct bufferinfo *view)
This is a C-API version of the releasebuffer function call. It checks to
make sure the object has the required function pointer and issues the call. Returns 0
on success and -1 (with an error raised) on failure. This function always
succeeds if there is no releasebuffer function for the object.
This is a C-API version of the releasebuffer function call. It checks
to make sure the object has the required function pointer and issues
the call. Returns 0 on success and -1 (with an error raised) on
failure. This function always succeeds if there is no releasebuffer
function for the object.
::
PyObject *PyObject_GetMemoryView(PyObject *obj)
Return a memory-view object from an object that defines the buffer interface.
If make_ro is non-zero then request that the memory is made read-only until
release buffer is called.
Return a memory-view object from an object that defines the buffer interface.
A memory-view object is an extended buffer object that should replace
the buffer object in Python 3K. It's C-structure is::
A memory-view object is an extended buffer object that could replace
the buffer object (but doesn't have to as that could be kept as a
simple 1-d memory-view object). It's C-structure is
::
typedef struct {
PyObject_HEAD
PyObject *base;
struct bufferinfo view;
int itemsize;
int flags;
int ndims;
Py_ssize_t *starts; /* slice starts */
Py_ssize_t *stops; /* slice stops */
Py_ssize_t *steps; /* slice steps */
} PyMemoryViewObject;
This is very similar to the current buffer object except offset has
been removed because ptr can just be modified by offset and a single
offset is not sufficient for the sub-offsets. Also the hash has been
removed because using the buffer object as a hash even if it is
read-only is rarely useful.
This is functionally similar to the current buffer object except only
a reference to base is kept. The actual memory for base must be
re-grabbed using the buffer-protocol, whenever it is actually
needed (after which it is immediately released).
Also, the format, ndims, shape, strides, and suboffsets have been
added. These additions will allow multi-dimensional slicing of the
memory-view object which can be added at some point. This object
always owns it's own shape, strides, and suboffsets arrays and it's
own format string, but always borrows the memory from the object
pointed to by base.
The getbuffer and releasebuffer for this object use the underlying
base object (adjusted as needed using the slice information). If the
number of dimensions of the base object (or the strides or the size)
has changed when a new view is requested, then the getbuffer will
trigger an error. Methods on the MemoryView object will allow
manual locking and unlocking of the underlying buffer.
The itemsize is a convenience and specifies the number of bytes
indicated by the format string if positive.
This memory-view object will support mult-dimensional slicing and be
the first object provided with Python to do so. Slices of the
memory-view object are other memory-view objects. When an "element"
from the memory-view is returned it is always a bytes object whose
format should be interpreted by the format attribute of the memoryview
object. The struct module can be used to "decode" the bytes in Python
if desired.
This object never reallocates ptr, shape, strides, subboffsets or
format and therefore does not need to keep track of how many views it
has exported.
The Python name will be
__builtin__.memory
Methods:
lock
unlock
__getitem__ (will support multi-dimensional slicing)
__setitem__ (will support multi-dimensional slicing)
tobytes (obtain a bytes-object of everything in the memory).
tolist (obtain a "nested" list of the memory. Everything
is interpreted into standard Python objects
as the struct module unpack would do).
Attributes (taken from the memory of the base object)
format
itemsize
shape
strides
suboffsets
size
readonly
ndim
It exports a view using the base object. It releases a view by
releasing the view on the base object. Because, it will never
re-allocate memory, it does not need to keep track of how many it has
exported but simple reference counting will suffice.
::
int PyObject_SizeFromFormat(char *)
int PyBuffer_SizeFromFormat(const char *)
Return the implied itemsize of the data-format area from a struct-style
description.
@ -432,65 +558,82 @@ description.
::
int PyObject_GetContiguous(PyObject *obj, void **buf, Py_ssize_t *len,
int fortran)
char **format, char fortran)
Return a contiguous chunk of memory representing the buffer. If a
copy is made then return 1. If no copy was needed return 0. If an
error occurred in probing the buffer interface, then return -1. The
contiguous chunk of memory is pointed to by ``*buf`` and the length of
that memory is ``*len``. If the object is multi-dimensional, then if
fortran is 1, the first dimension of the underlying array will vary
the fastest in the buffer. If fortran is 0, then the last dimension
will vary the fastest (C-style contiguous). If fortran is -1, then it
fortran is 'F', the first dimension of the underlying array will vary
the fastest in the buffer. If fortran is 'C', then the last dimension
will vary the fastest (C-style contiguous). If fortran is 'A', then it
does not matter and you will get whatever the object decides is more
efficient.
efficient. If a copy is made, then the memory must be freed by calling
``PyMem_Free``.
::
int PyObject_CopyToObject(PyObject *obj, void *buf, Py_ssize_t len,
int fortran)
char fortran)
Copy ``len`` bytes of data pointed to by the contiguous chunk of
memory pointed to by ``buf`` into the buffer exported by obj. Return
0 on success and return -1 and raise an error on failure. If the
object does not have a writeable buffer, then an error is raised. If
fortran is 1, then if the object is multi-dimensional, then the data
fortran is 'F', then if the object is multi-dimensional, then the data
will be copied into the array in Fortran-style (first dimension varies
the fastest). If fortran is 0, then the data will be copied into the
array in C-style (last dimension varies the fastest). If fortran is -1, then
the fastest). If fortran is 'C', then the data will be copied into the
array in C-style (last dimension varies the fastest). If fortran is 'A', then
it does not matter and the copy will be made in whatever way is more
efficient.
The last two C-API calls allow a standard way of getting data in and
These last three C-API calls allow a standard way of getting data in and
out of Python objects into contiguous memory areas no matter how it is
actually stored. These calls use the extended buffer interface to perform
their work.
::
int PyObject_IsContiguous(struct bufferinfo *view, int fortran);
int PyBuffer_IsContiguous(PyBuffer *view, char fortran);
Return 1 if the memory defined by the view object is C-style (fortran = 0)
or Fortran-style (fortran = 1) contiguous. Return 0 otherwise.
Return 1 if the memory defined by the view object is C-style (fortran
= 'C') or Fortran-style (fortran = 'F') contiguous or either one
(fortran = 'A'). Return 0 otherwise.
::
int PyBuffer_IsAligned(PyBuffer *view);
Return 1 if the memory at all elements of the array implied by the
view object is aligned
::
void PyObject_FillContiguousStrides(int *ndims, Py_ssize_t *shape,
void PyBuffer_FillContiguousStrides(int *ndims, Py_ssize_t *shape,
int itemsize,
Py_ssize_t *strides, int fortran)
Py_ssize_t *strides, char fortran)
Fill the strides array with byte-strides of a contiguous (C-style if
fortran is 0 or Fortran-style if fortran is 1) array of the given
shape with the given number of bytes per element.
::
int PyBuffer_FillInfo(PyBuffer *view, void *buf,
Py_ssize_t len, int readonly, int infoflags)
int PyObject_FillBufferInfo(struct bufferinfo *view, void *buf, Py_ssize_t len,
int readonly, int infoflags)
Fills in a buffer-info structure correctly for an exporter that can
only share a contiguous chunk of memory of "unsigned bytes" of the
given length. Returns 0 on success and -1 (with raising an error) on
error.
Fills in a buffer-info structure correctly for an exporter that can only share
a contiguous chunk of memory of "unsigned bytes" of the given length. Returns 0 on success
and -1 (with raising an error) on error
::
PyErr_BufferError
A new error object for returning buffer errors which arise because an
exporter cannot provide the kind of buffer that a consumer expects.
This will also be raised when a consumer requests a buffer from an
object that does not provide the protocol.
Additions to the struct string-syntax
@ -521,22 +664,29 @@ Character Description
':name:' optional name of the preceeding element
'X{}' pointer to a function (optional function
signature inside {})
' \n\t' ignored (allow better readability) -- this may already be true
' \n\t' ignored (allow better readability)
-- this may already be true
================ ===========
The struct module will be changed to understand these as well and
return appropriate Python objects on unpacking. Un-packing a
return appropriate Python objects on unpacking. Unpacking a
long-double will return a decimal object or a ctypes long-double.
Unpacking 'u' or 'w' will return Python unicode. Unpacking a
multi-dimensional array will return a list of lists. Un-packing a
pointer will return a ctypes pointer object. Un-packing a bit will
return a Python Bool. Spaces in the struct-string syntax will be
ignored. Unpacking a named-object will return a Python class with
attributes having those names.
multi-dimensional array will return a list (of lists if >1d).
Unpacking a pointer will return a ctypes pointer object. Unpacking a
function pointer will return a ctypes call-object (perhaps). Unpacking
a bit will return a Python Bool. White-space in the struct-string
syntax will be ignored if it isn't already. Unpacking a named-object
will return some kind of named-tuple-like object that acts like a
tuple but whose entries can also be accessed by name. Unpacking a
nested structure will return a nested tuple.
Endian-specification ('=','>','<') is also allowed inside the
string so that it can change if needed. The previously-specified
endian string is in force until changed. The default endian is '='.
Endian-specification ('!', '@','=','>','<', '^') is also allowed
inside the string so that it can change if needed. The
previously-specified endian string is in force until changed. The
default endian is '@' which means native data-types and alignment. If
un-aligned, native data-types are requested, then the endian
specification is '^'.
According to the struct-module, a number can preceed a character
code to specify how many of that type there are. The
@ -551,16 +701,21 @@ Examples of Data-Format Descriptions
====================================
Here are some examples of C-structures and how they would be
represented using the struct-style syntax:
represented using the struct-style syntax.
<named> is the constructor for a named-tuple (not-specified yet).
float
'f'
'f' <--> Python float
complex double
'Zd'
'Zd' <--> Python complex
RGB Pixel data
'BBB' or 'B:r: B:g: B:b:'
'BBB' <--> (int, int, int)
'B:r: B:g: B:b:' <--> <named>((int, int, int), ('r','g','b'))
Mixed endian (weird but possible)
'>i:big: <i:little:'
'>i:big: <i:little:' <--> <named>((int, int), ('big', 'little'))
Nested structure
::
@ -586,7 +741,9 @@ Nested array
int ival;
double data[16*4];
}
'i:ival: (16,4)d:data:'
"""i:ival:
(16,4)d:data:
"""
Code to be affected
@ -662,10 +819,12 @@ Examples
=========
Ex. 1
----------
-----------
This example shows how an image object that uses contiguous lines might expose its buffer.::
::
struct rgba {
unsigned char r, g, b, a;
};
@ -688,7 +847,9 @@ In order to access, say, the red value of the pixel at x=30, y=50, you'd use "li
So what does ImageObject's getbuffer do? Leaving error checking out::
int Image_getbuffer(PyObject *self, struct bufferinfo *view, int flags) {
::
int Image_getbuffer(PyObject *self, PyBuffer *view, int flags) {
static Py_ssize_t suboffsets[2] = { -1, 0 };
@ -710,7 +871,7 @@ So what does ImageObject's getbuffer do? Leaving error checking out::
}
int Image_releasebuffer(PyObject *self, struct bufferinfo *view) {
int Image_releasebuffer(PyObject *self, PyBuffer *view) {
self->view_count--;
return 0;
}
@ -721,33 +882,36 @@ Ex. 2
This example shows how an object that wants to expose a contiguous
chunk of memory (which will never be re-allocated while the object is
alive) would do that.::
alive) would do that.
int myobject_getbuffer(PyObject *self, struct bufferinfo *view, int flags) {
::
void *buf;
Py_ssize_t len;
int readonly=0;
int myobject_getbuffer(PyObject *self, PyBuffer *view, int flags) {
void *buf;
Py_ssize_t len;
int readonly=0;
buf = /* Point to buffer */
len = /* Set to size of buffer */
readonly = /* Set to 1 if readonly */
return PyObject_FillBufferInfo(view, buf, len, readonly, flags);
buf = /* Point to buffer */
len = /* Set to size of buffer */
readonly = /* Set to 1 if readonly */
return PyObject_FillBufferInfo(view, buf, len, readonly, flags);
}
/* No releasebuffer is necessary because the memory will never
be re-allocated so the locking mechanism is not needed
*/
/* No releasebuffer is necessary because the memory will never
be re-allocated so the locking mechanism is not needed
*/
Ex. 3
-----------
A consumer that wants to only get a simple contiguous chunk of bytes
from a Python object, obj would do the following::
from a Python object, obj would do the following:
::
struct bufferinfo view;
PyBuffer view;
int ret;
if (PyObject_GetBuffer(obj, &view, Py_BUF_SIMPLE) < 0) {
@ -767,7 +931,36 @@ from a Python object, obj would do the following::
}
Ex. 4
-----------
A consumer that wants to be able to use any object's memory but is
writing an algorithm that only handle contiguous memory could do the following:
::
void *buf;
Py_ssize_t len;
char *format;
if (PyObject_GetContiguous(obj, &buf, &len, &format, 0) < 0) {
/* error return */
}
/* process memory pointed to by buffer if format is correct */
/* Optional:
if, after processing, we want to copy data from buffer back
into the the object
we could do
*/
if (PyObject_CopyToObject(obj, buf, len, 0) < 0) {
/* error return */
}
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=========