Make BitArray.{slice_bits,slice_shots,__getitem__} raise IndexError when indices are not valid

[t-imamichi]

Summary

This PR updates BitArray.{slice_bits,slice_shots,__getitem__} to raise IndexError if indices are not valid.

Especially, __getitem__ raise IndexError with appropriate message as follows (ba[0, 0, 0] case).

from qiskit.primitives.containers import BitArray

ba = BitArray.from_counts({"0": 2, "1": 3})
ba = ba.reshape(1, 1)

try:
    ba[1]
except Exception as ex:
    print(type(ex), ex)
try:
    ba[0, 0, 0]
except Exception as ex:
    print(type(ex), ex)
try:
    ba[0, 0, 0, 0]
except Exception as ex:
    print(type(ex), ex)

main branch

<class 'IndexError'> index 1 is out of bounds for axis 0 with size 1
<class 'ValueError'> The input array must have at least two axes.
<class 'ValueError'> BitArrays cannot be sliced along the bits axis, see slice_bits() instead.

this PR

<class 'IndexError'> index 1 is out of bounds for axis 0 with size 1
<class 'IndexError'> BitArray cannot be sliced along the shots axis, use slice_shots() instead.
<class 'IndexError'> BitArray cannot be sliced along the bits axis, use slice_bits() instead.

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @ajavadia
• @levbishop
• @t-imamichi

[coveralls]

Pull Request Test Coverage Report for Build 9887440194

Details

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.009%) to 89.884%

---

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	5	91.6%
crates/qasm2/src/parse.rs	6	97.61%

Totals
Change from base Build 9876062430:	-0.009%
Covered Lines:	65741
Relevant Lines:	73140

---

💛 - Coveralls

[ElePT]

This looks like a straightforward fix that improves the BitArray user experience. I think it should be backported to 1.1 and 1.2.

[ElePT]

@Mergifyio backport stable/1.1

[mergify]

backport stable/1.1

✅ Backports have been created

• #12844 Make BitArray.{slice_bits,slice_shots,__getitem__} raise IndexError when indices are not valid (backport #12755) has been created for branch stable/1.1 but encountered conflicts