class A:
    def __buffer__(self, flags):
            return memoryview(bytes(8))
    def __release_buffer__(self, view):
            pass # do not need to do anything here, just needs to exist

b = bytearray(8)
m = memoryview(b) # now b.extend will raise an exception due to exports
b.extend(A())

In a debug build this crashes with Assertion failed: (!PyErr_Occurred()), function _PyType_Lookup, file typeobject.c, line 4707.

Reported by @chilaxan. I'll work on a fix later today.

Most likely, the fix will be to call PyErr_Fetch/PyErr_Restore around calls to Python __release_buffer__ methods.

Linked PRs

• gh-104371: Fix calls to __release_buffer__ while an exception is active #104378
• GH-104371: check return value of calling mv.release #104417