[docs] [issue15821] Improve docs for PyMemoryView_FromBuffer()

[Stefan Krah]

Stefan Krah added the comment:

This may be a bigger problem (grep for image_surface_get_data):

http://lists.cairographics.org/archives/cairo/2011-December/022563.html


The previous semantics for PyMemoryView_FromBuffer(view) were:

  1) If non-NULL, steal the view.obj reference with automatic
     decrement in PyBuffer_Release().

  2) Copy shape and strides to view.smalltable.



The new semantics for PyMemoryView_FromBuffer(view) are:

  1) If non-NULL, treat view.obj as a borrowed reference.

  2) Rely on the fact that shape and strides won't disappear.


2) means that returning PyMemoryView_FromBuffer(view) from
a view allocated on the stack is no longer safe. In all instances
people could migrate to PyMemoryView_FromMemory(), which is
both safe and more convenient, but code may be broken.

PyManaged_Buffer is designed to expect buffers from exporters,
where it is guaranteed that the buffers won't disappear,so it
won't be easy to keep backwards compatibility.

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priority: normal -> high

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<http://bugs.python.org/issue15821>
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