[issue29300] Modify the _struct module to use FASTCALL and Argument Clinic

[STINNER Victor]

STINNER Victor added the comment:

Martin Panter: """FYI Victor, you can make non-C-contiguous buffers by slicing memoryview:

>>> struct.unpack(">L", memoryview(b"1234")[::-1])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
BufferError: memoryview: underlying buffer is not C-contiguous"""

Oh, it means that the Argument Clinic change doesn't add new checks on the buffer? In Python 3.6, memory_getbuf() raises an exception in the following code:

    if (!REQ_STRIDES(flags)) {
        if (!MV_C_CONTIGUOUS(baseflags)) {
            PyErr_SetString(PyExc_BufferError,
                "memoryview: underlying buffer is not C-contiguous");
            return -1;
        }
        view->strides = NULL;
    }

I undersrtand that memory_getbuf() is smart enough to raise an exception becaues the buffer is not contiguous. But a weaker implementation of getbuffer may not implement such check, whereas getbuffer() double check that the buffer is C-contiguous. Am I right?

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29300>
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