Fix list slicing with a zero stop or negative indices#394
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gottostartsomewhere wants to merge 1 commit into
Open
Fix list slicing with a zero stop or negative indices#394gottostartsomewhere wants to merge 1 commit into
gottostartsomewhere wants to merge 1 commit into
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ListBase.__getitem__ resolved slice bounds with `key.stop or self["count"]`, which treats a stop of 0 as unset. As a result obj_list[:0] returned the whole list instead of an empty one, and negative indices were mishandled. Use slice.indices(len(self)), which correctly normalises None, negative and out-of-range bounds. Extend the slice test with zero-stop and negative cases.
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Problem
ListBase.__getitem__resolves slice bounds like this:Because
0is falsy,key.stop or self["count"]treats a stop of 0 as "unset". So a slice such asobj_list[:0](conventionally empty) returns the entire list. Negative indices are also mishandled (e.g.obj_list[-2:]produces a wrong, over-long result), since raw negative bounds are passed straight torange().Fix
Use
slice.indices(len(self)), the standard way to normalise slice bounds — it correctly handlesNone, negative, and out-of-range start/stop/step. All previously-passing slices are unchanged.Tests
Extended
test_list_supports_slice_sequenceswith a zero-stop case (methods[:0]→ empty) and a negative case (methods[-2:]→ last two). Both fail onmainand pass with this change; the existing slice assertions continue to pass.