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Truncate fractional seconds per UTS 35 #1292

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Merged
akx merged 1 commit into from
Nov 4, 2026
+21 −8
Merged

Truncate fractional seconds per UTS 35 #1292

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9 changes: 5 additions & 4 deletions babel/dates.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1636,11 +1636,12 @@ def format_period(self, char: str, num: int) -> str:
def format_frac_seconds(self, num: int) -> str:
""" Return fractional seconds.

Rounds the time's microseconds to the precision given by the number \
of digits passed in.
Truncates the time's microseconds to the number of digits passed in,
as specified by UTS #35.
"""
value = self.value.microsecond / 1000000
return self.format(round(value, num) * 10**num, num)
micro = self.value.microsecond
frac = micro // 10**(6 - num) if num <= 6 else micro * 10**(num - 6)
return self.format(frac, num)

def format_milliseconds_in_day(self, num):
msecs = (
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2 changes: 1 addition & 1 deletion docs/dates.rst
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Expand Up @@ -206,7 +206,7 @@ Time Fields
+----------+--------+--------------------------------------------------------+
| Second | ``s`` | Use one or two for zero places padding. |
| +--------+--------------------------------------------------------+
| | ``S`` | Fractional second, rounds to the count of letters. |
| | ``S`` | Fractional second, truncates to the count of letters. |
| +--------+--------------------------------------------------------+
| | ``A`` | Milliseconds in day. |
+----------+--------+--------------------------------------------------------+
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18 changes: 15 additions & 3 deletions tests/test_date_time_format.py
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Expand Up @@ -166,20 +166,32 @@ def test_fractional_seconds():
t = time(8, 3, 9, 799)
assert DateTimeFormat(t, locale='en_US')['S'] == '0'
t = time(8, 3, 1, 799)
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '0008'
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '0007'
t = time(8, 3, 1, 34567)
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '0346'
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '0345'
t = time(8, 3, 1, 345678)
assert DateTimeFormat(t, locale='en_US')['SSSSSS'] == '345678'
t = time(8, 3, 1, 799)
assert DateTimeFormat(t, locale='en_US')['SSSSS'] == '00080'
assert DateTimeFormat(t, locale='en_US')['SSSSS'] == '00079'


def test_fractional_seconds_zero():
t = time(15, 30, 0)
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '0000'


def test_fractional_seconds_truncation_does_not_carry():
t = time(1, 2, 3, 990000)
assert DateTimeFormat(t, locale='en_US')['S'] == '9'
t = time(1, 2, 3, 999500)
assert DateTimeFormat(t, locale='en_US')['SS'] == '99'
t = time(1, 2, 3, 999999)
assert DateTimeFormat(t, locale='en_US')['S'] == '9'
assert DateTimeFormat(t, locale='en_US')['SS'] == '99'
assert DateTimeFormat(t, locale='en_US')['SSSS'] == '9999'
assert DateTimeFormat(t, locale='en_US')['SSSSSSSS'] == '99999900'


def test_milliseconds_in_day():
t = time(15, 30, 12, 345000)
assert DateTimeFormat(t, locale='en_US')['AAAA'] == '55812345'
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