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Fix format_timespan() rounding the smallest unit past a whole unit of the next one #86

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Fix format_timespan() rounding the smallest unit past a whole unit of the next one #86

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10 changes: 10 additions & 0 deletions humanfriendly/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -437,6 +437,16 @@ def format_timespan(num_seconds, detailed=False, max_units=3):
result = []
num_seconds = decimal.Decimal(str(num_seconds))
relevant_units = list(reversed(time_units[0 if detailed else 3:]))
# Round the total number of seconds to the precision that will
# eventually be displayed for the smallest unit before decomposing
# it into units below. Rounding only the smallest unit's count in
# isolation (as used to happen here) can inflate its displayed
# value up to or past a whole unit of the next larger unit that
# was already emitted, producing nonsensical output such as
# "1 minute and 60 seconds" instead of "2 minutes".
smallest_divider = decimal.Decimal(str(relevant_units[-1]['divider']))
quantum = smallest_divider / 100
num_seconds = (num_seconds / quantum).to_integral_value(rounding=decimal.ROUND_HALF_EVEN) * quantum
for unit in relevant_units:
# Extract the unit count from the remaining time.
divider = decimal.Decimal(str(unit['divider']))
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8 changes: 8 additions & 0 deletions humanfriendly/tests.py
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Expand Up @@ -449,6 +449,14 @@ def test_format_timespan(self):
assert '1 second and 15 milliseconds' == format_timespan(1.015, detailed=True)
assert '10 seconds and 15 milliseconds' == format_timespan(10.015, detailed=True)
assert '1 microsecond and 50 nanoseconds' == format_timespan(0.00000105, detailed=True)
# Test that rounding the smallest displayed unit never produces a
# count that has reached (or gone past) a whole unit of the next
# larger, already emitted unit, which used to render nonsensical
# output such as "1 minute and 60 seconds" instead of properly
# carrying the extra unit over.
assert '2 minutes' == format_timespan(119.999)
assert '1 hour' == format_timespan(3599.999)
assert '1 minute, 59 seconds and 999 milliseconds' == format_timespan(119.999, detailed=True)
# Test the datetime.timedelta support:
# https://github.com/xolox/python-humanfriendly/issues/27
now = datetime.datetime.now()
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