fix: carry filesize suffix when mantissa rounds up to base

[patchwright]

Problem

All three public functions (traditional, binary, decimal) can produce impossible output like "1,024.0 KB" instead of "1.0 MB" for values just below a unit boundary.

Root cause: _to_str picks the suffix from the unrounded value, then formats the mantissa — which can round up to base, producing an impossible result.

filesize.decimal(999_999) # '1,000.0 kB' ← should be '1.0 MB'filesize.traditional(1024**2-1) # '1,024.0 KB' ← should be '1.0 MB'filesize.binary(1024**2-1) # '1,024.0 KiB' ← should be '1.0 MiB'

Fix

Convert suffixes to a list before the loop. After computing the mantissa, round and compare against base. If the rounded value hits base, step up one suffix and recompute:

mantissa=base*size/unitifround(mantissa, 1) >=baseandi-1<len(suffixes):
suffix=suffixes[i-1]
mantissa=size/unit

Math: when the current unit is base**i, dividing size by that same unit gives the value in the next suffix (whose denominator is base**(i+1), which divides into base * size / base**(i+1) = size / base**i = size / unit).

Also removes the existing TODO comment that flagged this exact issue.

Tests

Added test_rollover_decimal, test_rollover_traditional, and test_rollover_binary covering the unit boundaries for all three functions.

[lurch]

Ahhh, the fun of floating-point rounding 😆

I wonder if it might also be worth adding some unit-tests for the boundary-values? E.g.

>>>traditional(1996)
'1.9 KB'>>>traditional(1997)
'2.0 KB'>>>decimal(1950)
'1.9 kB'>>>decimal(1951)
'2.0 kB'>>>binary(1996)
'1.9 KiB'>>>binary(1997)
'2.0 KiB'

[patchwright]

Good call, those within-unit boundary cases are worth pinning down separately from the rollover ones. Added a test_rounding_boundaries covering your exact examples for all three functions:

traditional(1996) =="1.9 KB"traditional(1997) =="2.0 KB"decimal(1950) =="1.9 kB"decimal(1951) =="2.0 kB"binary(1996) =="1.9 KiB"binary(1997) =="2.0 KiB"

All pass on the branch. Thanks for the review.

[lurch]

Is it also worth checking the boundaries at e.g.

>>>decimal(999_949)
'999.9 kB'>>>decimal(999_950)
'1.0 MB'

or do you think those are sufficiently covered by the existing tests?

[patchwright]

Good catch. Those weren't covered: test_rollover_decimal only pinned the far end at 999_999, and test_rounding_boundaries is within-unit, so the first-flip at 999_950 had no test. Both behave as expected: decimal(999_949) stays '999.9 kB', decimal(999_950) rolls to '1.0 MB'.Added that pair. traditional and binary share the same carry logic and had the same gap (their rollover tests only checked 1024**2 - 1), so I pinned their first-flip too: 1_048_524 stays '1,023.9 KB'/'1,023.9 KiB', 1_048_525 rolls to '1.0 MB'/'1.0 MiB'. Pushed in the latest commit, full suite green.

[patchwright]

FYI on the red checks: the failing jobs (test (2.7), (3.5) through (3.10), (pypy-2.7/3.6/3.7)) all fail identically on master @77a8562, so they are pre-existing failures on the EOL-Python jobs rather than anything from this diff. As a small upside, lint (typecheck) is failing on master but passes on this branch. The rollover tests added here pass on supported Pythons (3.10+).

[patchwright]

Quick correction to my last CI note: I called those red test (...) jobs EOL-Python failures matching master. Looking at the check annotations, that is not quite right. GitHub is auto-failing every test job because .github/workflows/test.yml (line 45) uses actions/upload-artifact@v2, which was deprecated and auto-fails per the 2024-02-13 policy. It is not from this diff: the lint jobs pass (including typecheck); only the test jobs hit the deprecated-action fail. Bumping upload-artifact to v4 would clear the matrix. I will leave that to you since it is CI infra, not the filesize change.

[patchwright]

Checking back in — it's been about a month. The content side (filesize suffix + the boundary tests you asked for) has been stable since 07-07; the only red is the pre-existing upload-artifact@v2 deprecation on the test matrix (unrelated to this diff, lint jobs all pass). Let me know if there's anything else you'd like changed.