Create Python buffer object from C++ pointer using SWIG?

Question

I would like to create a Python buffer object (either writable or not) from a C++ pointer, such that it can be passed to the numpy.frombuffer function. Can someone let me know how to do it?

Here is my example SWIG-wrapped C++ function which returns a pointer:

uint8_t* some_function() {return new uint8_t[200];}

After SWIG wrap it, I followed this post to create a buffer object in python:

x = some_function()
b = buffer_frompointer(x)
z = numpy.frombuffer(b, dtype=numpy.uint8)

The last statement returns an error saying the __buffer__ attribute is not found. I guess this is because the variable b here is not really a buffer object in the python sense. So what shall I do?

ps. I don't want an additional copy of the memory when creating the numpy array.

ps. Let's not worry about the memory leak problem for now.

UPDATE:

I'm still interested in a solution to this question, but in case no one answers it, I'll go with a workaround in another question I asked, although that solution is not preferred because of the use of deprecated interfaces.

Hwa · Accepted Answer · 2018-05-17 07:11:42Z

0

import ctypes, numpy
bptr = int(b.cast())
barray = ctypes.c_byte*200
barray = barray.from_address(bptr)
z = numpy.ctypeslib.as_array(barray)

answered May 17, 2018 at 7:11

Hwa

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1 Comment

L. Guthardt Over a year ago

Please don't post answers that contain only code. Go ahead and explain your solution how you solved OP's issue.

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