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As I following up to the issue #21831, I don't understand why memoryview[2**100:] doesn't raise an overflow error!? It looks like a bug.
Attached patch changes the behaviour to raise an OverflowError.

It's a slice of length zero:
>>> b = bytearray([1,2,3,4])
>>> m = memoryview(b)
>>>
>>> b2 = b[2**100:]
>>> m2 = m[2**100:]
>>>
>>> list(b2)
[]
>>> list(m2)
[]
>>>

Victor, shall we close this? The behavior is basically as specified:
"The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty."

#21831 was about size not being properly clamped. Here it is.

If the behaviour is well expected, I suggest to add an unit test: memoryview_test_large_slice.patch.

Memoryview should definitely have the same slice tests as other sequence objects. Go ahead and check.
I believe slice clamping itself should now be done by slice.indices, not by each class.
 S.indices(len) -> (start, stop, stride)
 
 Assuming a sequence of length len, calculate the start and stop
 indices, and the stride length of the extended slice described by
 S. Out of bounds indices are clipped in a manner consistent with the
 handling of normal slices.
It seems like this was written before it was normal for every slice to have a step (stride), defaulting to None/1. It definitely comes from 2.x, before __getslice__ was folded into __getitem__
I expect builtin 3.x sequence objects should all use something like the C equivalent of
 def __getitem__(self, ob):
 if type(ob) is slice:
 start, stop, stride = ob.indices(self.len)
 ...

Since the rewrite in 3.3 many memoryview tests are actually in test_buffer.py.

And Terry is right, the actual slice clamping happens in
PySlice_GetIndicesEx(), which should always produce values
that are in the correct range. Hence the tests focus on
slices that already are in the correct range.
I'm not sure if PySlice_GetIndicesEx() itself has tests somewhere.

Seaching for "PySlice_GetIndicesEx" in .../test/*.py with Idle Find in Files did not turn up any hits. However, test.test_slice.test_indices() has several tests of clamping, including 2**100 in various combinations. The use of 2**100 was was added in #14794 to test successful removal of the Overflow that Victor requested. I don't see that there is any patch needed. Victor, if you find a deficiency, reopen or open a new issue.