Fix format_size() rounding rollover at unit boundaries#82
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format_size() chooses the unit by comparing the raw byte count to each
divider, then rounds the mantissa with round_number() afterward. When the
mantissa rounds up to the base (e.g. 999999 bytes is 999.999 KB, which rounds
to '1000 KB'), the already-chosen unit is left stale:
>>> format_size(999999)
'1000 KB' # expected '1 MB'
>>> format_size(999999999)
'1000 MB' # expected '1 GB'
>>> format_size(1024 ** 2 - 1, binary=True)
'1024 KiB' # expected '1 MiB'
Fix: after rounding, if the mantissa has reached the base and a larger unit
is available, carry into that next unit and re-render. Added regression cases
to test_format_size (they fail before this change, pass after); all existing
assertions are unchanged.
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Problem
format_size()picks the unit by comparing the raw byte count to each divider, then rounds the mantissa withround_number()afterward. When rounding pushes the mantissa up to the base, the already-chosen unit is left stale:999999bytes is999.999 KB;'%.2f'rounds that to1000, but the unit was already fixed atKB, so the output reads1000 KBinstead of1 MB. The same happens at every decimal and binary boundary.Fix
After rounding, if the mantissa has reached the base (
1000decimal /1024binary) and a larger unit is available, carry into that next unit and re-render. Values already at the largest unit (YB/YiB) are unaffected, as are all values that don't round across a boundary.Tests
Added regression assertions to
test_format_sizecovering the decimal and binary boundaries. They fail on the current code and pass with this change; every existing assertion is unchanged.