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Various ways to get a current timestamp or convert a timestamp to a `datetime`
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| #!/usr/bin/env python3 | |
| ''' | |
| I spent way too much time messing with timestamps. | |
| A timestamp is the number of seconds elapsed since the epoch. | |
| A unix timestamp uses the unix epoch, which is defined as | |
| 1970-01-01T00:00:00+00:00 | |
| Takeaways | |
| * the `datetime` module handles two different types of datetimes: | |
| 1. "naive" times don't know their timezone | |
| 2. "aware" times do know their timezone | |
| * most functions treat a naive time as a local time | |
| * `datetime.utcnow()` is evil: it creates a naive time that is not local time | |
| * ditto for `datetime.utcfromtimestamp()` | |
| * use `datetime.now(UTC)` or `datetime.fromtimestamp(t,UTC)` instead | |
| * avoid using naive times | |
| ''' | |
| import time | |
| from datetime import datetime as DT | |
| from datetime import timezone | |
| UTC = timezone.utc | |
| EPOCH = DT.fromtimestamp(0,UTC) | |
| TEMPLATE ="{:24} {:10d} {:32} {:32} {:32}" | |
| print("Unix epoch:",EPOCH.isoformat()) | |
| print() | |
| def prtime(label,dt,template=TEMPLATE): | |
| ts = round(dt.timestamp()) | |
| plain = dt.isoformat() | |
| local = dt.astimezone().isoformat() | |
| utc = dt.astimezone(UTC).isoformat() | |
| print(template.format(label,ts,plain,local,utc)) | |
| def mktime(label,func,*args,**kw): | |
| dt = func(*args,**kw) | |
| prtime(label,dt) | |
| return dt | |
| now = time.time() | |
| rnow = round(now) | |
| dates = [ mktime(*args) for args in | |
| ( | |
| # naive. wrong unless local time is UTC | |
| ("DT.utcfromtimestamp(t)",DT.utcfromtimestamp,now), | |
| # correct, but naive | |
| ("DT.fromtimestamp(t)",DT.fromtimestamp,now), | |
| # correct and aware | |
| ("DT.fromtimestamp(t,UTC)",DT.fromtimestamp,now,UTC), | |
| # naive. wrong unless local time is UTC | |
| ("DT.utcnow()",DT.utcnow), | |
| # correct, but naive | |
| ("DT.now()",DT.now), | |
| # correct and aware | |
| ("DT.now(UTC)",DT.now,UTC), | |
| ) | |
| ] | |
| # these should all represent approximately the same time | |
| for d in dates: | |
| print(round(d.timestamp())==rnow) |
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note that
utcfromtimestamp()has the same problem asutcnow()