[Maintenance] Tidy up datetime usage for new python versions

[sfayer]

Hi,

In datetime.datetime, the utcnow() & utcfromtimestamp() functions are deprecated from python3.12: The replacements for these have been available for a long time, so I suggest tidying them up. There are a few other linked smaller tasks:

• There are a few uses of strftime("%s") which has better alternatives.

• DIRAC/src/DIRAC/Core/Security/test/Test_X509Chain.py

  Line 64 in 48c1170

  NO_LATER_THAN_2050_IN_SEC = int((datetime.strptime("2049-12-31", "%Y-%M-%d") - datetime.now()).total_seconds())

  The %M specifier is minutes, not months, so it's off by ~11 months.
• There are some uses of datetime.now(), which may well run into issues around daylight-savings changes. These should all be checked and probably converted to UTC or another timezone aware option.

I'm thinking this could be a task for @martynia ?

Regards,
Simon

[ryuwd]

These parts (involving usage of old-vs-new timestamps) of the codebase are extremely fragile and if these changes are to be made they must be accompanied with rigorous unit testing

[aldbr]

ddev: datetime changes have been controversial, and these ones will still be supported in latest versions of python (e.g. 3.14) so we close the issue.

[sfayer]

Hi,

I'm reopening this, please see #8636 for details of my proposal on how this can be safely done (tl;dr: continue to use timezoneless objects in DIRAC, just replace the functions for getting them with our own non-deprecated versions). Hopefully we can discuss at next ddev...

Regards,
Simon