Implement LazySequenceCopy.pop(i)
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tybug
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Zac-HD
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| # this would be more robust as a stateful test, where each rule is a list operation | ||
| # on (1) the canonical python list and (2) its LazySequenceCopy. We would assert | ||
| # that the return values and lists match after each rule, and the original list | ||
| # is unmodified. |
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I agree that this would be nice but is not merge-blocking important.
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hypothesis-python/src/hypothesis/internal/conjecture/junkdrawer.py
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| shrunk = minimal(st.sampled_from(LargeFlag), lambda f: bit_count(f.value) > 1) | ||
| # Ideal would be (bit0 | bit1), but: | ||
| # minimal(st.sets(st.sampled_from(range(10)), min_size=3)) == {0, 8, 9} # not {0, 1, 2} | ||
| assert shrunk == LargeFlag.bit0 | LargeFlag.bit63 # documents actual behaviour |
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Nice, I remember scratching my head over this!
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thanks to your comment here, it was the only reason I looked into this 🙂
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Looks like we're no longer triggering the hypothesis/hypothesis-python/src/hypothesis/internal/conjecture/engine.py Lines 379 to 382 in 4e77eea |
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that coverage was hopefully fixed in #3991. I've rebased on master, let's see how it goes |
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UniqueSampledListStrategyusesLazySequenceCopyto pop elements from the list. BecauseLazySequenceCopyonly implemented pop-from-end, we swapped the element we wanted to pop to the end before popping. But this leaves the list in a bad state for shrinking: ifi = 0, we just swapped the last element, which is the most complicated in shrinking order, to the front of the list, leaving it there for future passes. This means an ir tree of[0, 0, 0]indicating the first three elements of the sequence corresponds to{0, 8, 9}forsets(range(10)).The solution is properly implementing
.pop(i). I've applied this in other places we use the swap trick, though I'm less confident thanUniqueSampledListStrategythat this is not a behavioral change.