I'm trying to find a way to create a ctypes array from the underlying memory buffer exposed by an array.array object. The ctypes.Array.from_buffer function isn't documented, but I did find the source code in _ctypes.c around line 497. It's not clear to me where the problem might be.


Code to reproduce it below:

import array, ctypes
a1 = array.array('l')
a1.fromlist(range(10))
ctypes.Array.from_buffer(a1)
#Segfault

You have to subclass ctypes.Array with a _type_ and _length_. But ctypes types also implement sequence repetition (*) to facilitate creating array types. For example:

    import array, ctypes
    a1 = array.array('l')
    a1.fromlist(range(10))
    c1 = (ctypes.c_long * 10).from_buffer(a1)

    >>> c1[:]
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    >>> c1[0] = 42
    >>> a1[0]
    42

That said, it's way too easy to segfault this. Why not simply fail the call in this case? e.g.

    StgDictObject *dict = PyType_stgdict(type);
    if (!dict) {
        PyErr_SetString(PyExc_TypeError,
                    "abstract class");
        return NULL;
    }

Here is a patch implementing Eryk’s suggestion, for both from_buffer() and from_buffer_copy() methods. This is exactly how it is already handled for Array.from_address(). The two buffer methods were added more recently than from_address().

New changeset 5f061870d49c by Martin Panter in branch '3.5':
Issue #25659: Change assert to TypeError in from_buffer/_copy()
https://hg.python.org/cpython/rev/5f061870d49c

New changeset 1253ef20c947 by Martin Panter in branch '3.6':
Issue #25659: Merge ctypes fix from 3.5
https://hg.python.org/cpython/rev/1253ef20c947

New changeset 821da4891051 by Martin Panter in branch 'default':
Issue #25659: Merge ctypes fix from 3.6
https://hg.python.org/cpython/rev/821da4891051

New changeset 4de956751cf1 by Martin Panter in branch '2.7':
Issue #25659: Change assert to TypeError in from_buffer/_copy()
https://hg.python.org/cpython/rev/4de956751cf1