Python 3 datetime.fromtimestamp not working for 1 microsecond

Question

I want to save datetimes with microsecond resolution as timestamps. But it looks like the Python 3 datetime module lost one microsecond at boot time. To test this, create a script:

test_datetime.py

from random import randint
from datetime import datetime

now = datetime.now()

for n in range(1000):
    d = datetime(year=now.year, month=now.month, day=now.day,
            hour=now.hour, minute=now.minute, second=now.second,
            microsecond=randint(0,999999))

    ts = d.timestamp()
    d2 = datetime.fromtimestamp(ts)

    assert d == d2, 'failed in pass {}: {} != {}'.format(n, d, d2)

python3 test_datetime.py always crash for one microsecond:

Traceback (most recent call last):
  File "test_datetime.py", line 14, in <module>
    assert d == d2, 'failed in pass {}: {} != {}'.format(n, d, d2)
AssertionError: failed in pass 4: 2014-07-02 11:51:46.984716 != 2014-07-02 11:51:46.984715

Can this behavior be accepted? Should we not rely on datetime.fromtimestamp if we want to get resolution in microseconds?

Answer 1

. , , , .

1404313854.442585 , . :

>>> dt = datetime(2014, 7, 2, 16, 10, 54, 442585)
>>> dt.timestamp()
1404313854.442585
>>> format(dt.timestamp(), '.20f')
'1404313854.44258499145507812500'

442585, . 442585, , , 1 , , 0.991455078125 , 442584.

, datetime, 1 .

, float; , , dt.fromtimestamp(seconds).replace(microsecond=microseconds).

PEP-410 ( .Decimal type ) . PEP , float.

Answer 2

- POSIX, "". datetime.fromtimestamp() " , POSIX, , time.time()", " , , , 1 .

, , , . .

EDIT: , datetime .

from datetime import datetime
baset = datetime.now()

dodgy = []
for i in range(1000000):
    d = baset.replace(microsecond=i)
    ts = d.timestamp()
    if d != datetime.fromtimestamp(ts):
        dodgy.append(i)
print(len(dodgy))

499 968 "" , .