BUG: gh-10882 may have broken ctypes compatibility in older versions of python

#10882 changed the behavior of np.array from.

• Try to get a PEP3118 buffer interface
  • Try to convert the buffer interface into an array
  • If the buffer interface is not correct, try __array_interface__ instead
  • sometimes call abort() due to bad error silencing (#6741)
• If there’s no buffer interface, try __array_interface__ instead

To

• Try to get a PEP3118 memory view
  • Try to convert the buffer interface into an array
  • If the buffer interface is not correct, fail and tell the user that something is wrong
• If there’s no buffer interface, try __array_interface__ instead

This means that objects which incorrectly implement the buffer interface now fail loudly, rather than silently-or-with-abort().

Unfortunately, prior to python/cpython#31, (before 2.7.14 / 3.6.3 / 3.7.0) ctypes did not implement the buffer interface correctly for integer types (the format and itemsize didn’t match)

Do we have a minimum supported patch version of python? If so, should we enable tests for it so that this doesn’t happen again?

[eric-wieser]

I could try tweaking #10882 to have a special case for ctypes objects,

[vadimkantorov]

I also stumbled on this: I have unrelated buffer interface (inherited from ctypes impl) and my custom array_interface that I’d like to be used