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Subsequent datetime.now() calls return the same datetime #124832
Description
Bug report
Bug description:
Subsequent datetime.now() may return the same moment in time.
from datetime import datetime, UTC
now1 = datetime.now(UTC)
for i in range(10_000):
a = i
now2 = datetime.now(UTC)
assert now1 < now2 assert now1 < now2
^^^^^^^^^^^
AssertionError
This does seem to work as expected:
from time import sleep
from datetime import datetime, UTC
now1 = datetime.now(UTC)
sleep(0.000_000_001)
now2 = datetime.now(UTC)
assert now1 < now2I'm not sure if this is a bug, but at least it's a documentation issue.
There's nothing in the docs explicitly indicating this behavior.
CPython versions tested on:
3.12
Operating systems tested on:
Windows
Linked PRs
- gh-124832: Add a note to indicate that
datetime.nowmay return the same instant #124834 - [3.13] gh-124832: Add a note to indicate that
datetime.nowmay return the same instant (GH-124834) #125145 - [3.12] gh-124832: Add a note to indicate that
datetime.nowmay return the same instant (GH-124834) #125146
Activity
vstinner commentedon Oct 1, 2024
Test with Python 3.13, it got better clocks: https://docs.python.org/dev/whatsnew/3.13.html#time
On Python 3.12, it's more likely that two consecutive calls to datetime.now() gives the same microseconds.
vstinner commentedon Oct 1, 2024
It's not a bug.
What do you expect in the doc?
spacemanspiff2007 commentedon Oct 1, 2024
I understand and suspected as much.
A warning that due to the clock resolution it's possible that two
datetime.now()calls can return the same time even though a "substantial" amount of time has passed.I had some tests failing which check that a datetime value which was updated was in the future.
That failed and I could not figure out why. I supplied
UTCas tz because the docs mention it might increase precision but with no success.A warning or hint would have been nice which I tried to add in the PR.
gh-124832: Add a note to indicate that `datetime.now` may return the …
pythongh-124832: Add a note to indicate that `datetime.now` may retur…
pythongh-124832: Add a note to indicate that `datetime.now` may retur…
[3.13] gh-124832: Add a note to indicate that `datetime.now` may retu…
[3.12] gh-124832: Add a note to indicate that `datetime.now` may retu…
pythongh-124832: Add a note to indicate that `datetime.now` may retur…