Fix _prettyprint after 'for i in range' changed to 'for i, val in enumerate'.

[jpivarski]

Just FYI @henryiii: changing

for i in range(len(out)):
    if i > 0:
        out[i] = " " + out[i]
    else:
        out[i] = "[" + out[i]
    if i < len(out) - 1:
        out[i] = out[i] + ","
    else:
        out[i] = out[i] + "]"

into a for loop with

for i, val in enumerate(out):

and all out[i] on the right-hand side of assignments converted into val broke this functionality. The original for loop relied on a side-effect in which out[i] was changed twice. Using an assigned-once name, val, prevented the first change from being seen in the final result.

I repeatedly run into cases in which side-effect turn out to be a bad idea (there's really something to this pure functional paradigm), and this could be counted as one of them. But side-effect based programming is a part of ordinary Python use and I wanted to bring to your attention that there are corner-cases like this in which for i in range(len(XYZ)) → for i, val in enumerate(XYZ) can be dangerous. Not to avoid these refactorings, but to keep an eye out for them!

(Also, I haven't yet checked the history to be sure that that's how this bug crept in, I'm just guessing that because it looks like it.)

[codecov]

Codecov Report

Merging #1384 (1b02d5b) into main (b2fd2be) will decrease coverage by 0.85%.
The diff coverage is 54.30%.

Impacted Files	Coverage Δ
src/awkward/_v2/_connect/cling.py	0.00% <0.00%> (ø)
src/awkward/_v2/_connect/cuda/__init__.py	0.00% <0.00%> (ø)
src/awkward/_v2/_lookup.py	97.50% <0.00%> (ø)
src/awkward/_v2/_prettyprint.py	66.09% <0.00%> (+2.29%)	⬆️
src/awkward/_v2/identifier.py	55.69% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_from_jax.py	75.00% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_to_jax.py	75.00% <0.00%> (ø)
src/awkward/_v2/operations/io/ak_from_parquet.py	75.00% <0.00%> (ø)
src/awkward/_v2/operations/io/ak_to_parquet.py	75.00% <0.00%> (ø)
src/awkward/_v2/operations/structure/ak_firsts.py	75.00% <0.00%> (ø)
... and 152 more

[henryiii]

I tried to watch for this, I know I avoided converting at least 1-2 because this side effect was being used. It's quite subtle - the new version is much better, IMO, since the reader can immediately see it's being intentionally reassigned.