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#! /usr/bin/env python
"""Python 3.x buffer-handling (currently just for bytes/bytearray types)
"""
import ctypes,sys
_fields_ = [
('buf',ctypes.c_void_p),
('obj',ctypes.py_object),
('len',ctypes.c_size_t),
('itemsize',ctypes.c_size_t),
('readonly',ctypes.c_int),
('ndim',ctypes.c_int),
('format',ctypes.c_char_p),
('shape',ctypes.POINTER(ctypes.c_size_t)),
('strides',ctypes.POINTER(ctypes.c_size_t)),
('suboffsets',ctypes.POINTER(ctypes.c_size_t)),
]
if sys.version_info[0] < 3:
_fields_.extend( [
('internal',ctypes.c_void_p),
] )
else:
# Sigh, this structure seems to have changed with Python 3.x...
_fields_.extend( [
('smalltable',ctypes.c_size_t*2),
('internal',ctypes.c_void_p),
] )
class Py_buffer(ctypes.Structure):
"""Wrapper around the Python buffer structure..."""
_fields_ = _fields_
@property
def dims( self ):
return self.shape[:self.ndim]
def __del__( self ):
# TODO: use a weakref
ReleaseBuffer( self )
BUFFER_POINTER = ctypes.POINTER( Py_buffer )
PyBUF_SIMPLE = 0
PyBUF_WRITABLE = PyBUF_WRITEABLE = 0x0001
PyBUF_ND = 0x0008
PyBUF_STRIDES = (0x0010 | PyBUF_ND)
PyBUF_CONTIG = (PyBUF_ND | PyBUF_WRITABLE)
PyBUF_CONTIG_RO = (PyBUF_ND)
try:
CheckBuffer = ctypes.pythonapi.PyObject_CheckBuffer
CheckBuffer.argtypes = [ctypes.py_object]
CheckBuffer.restype = ctypes.c_int
except AttributeError as err:
# Python 2.6 doesn't appear to have CheckBuffer support...
CheckBuffer = lambda x: True
GetBuffer = ctypes.pythonapi.PyObject_GetBuffer
GetBuffer.argtypes = [ ctypes.py_object, BUFFER_POINTER, ctypes.c_int ]
GetBuffer.restype = ctypes.c_int
ReleaseBuffer = ctypes.pythonapi.PyBuffer_Release
ReleaseBuffer.argtypes = [ BUFFER_POINTER ]
ReleaseBuffer.restype = None
def test():
for x in [
b'this and that', # sigh, 2to3 converts this to unicode... I *mean* an 8-bit buffer
# These are the things you'd have thought might support it...
#(ctypes.c_int * 3)( 1,2,3 ),
#numpy.arange(0,3,dtype='b'),
]:
buf = Py_buffer()
assert CheckBuffer( x )
result = GetBuffer( x, buf, PyBUF_CONTIG_RO )
assert result == 0, "Retrieval of buffer failed"
print('length:', buf.len)
print('readonly', buf.readonly)
print('format', buf.format)
print('ndim', buf.ndim)
print('shape', buf.shape[:buf.ndim])
print('dims', buf.dims )
print('c data pointer',buf.buf)
assert buf.len == len(x), "Mismatch in size of buffer (%s, expected %s)"%(buf.len,len(x))
if __name__ == "__main__":
test()
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