[Dev] `datetime.datetime.utcnow()` deprecated and replacement breaks `strptime`

[DanielYang59]

datetime.datetime.utcnow() deprecated

See discussion in https://github.com/materialsproject/pymatgen/pull/3705#discussion_r1537225117, datetime.datetime.utcnow() is marked as deprecated and might be removed after Python 3.12.

The same issue has been reported to monty as well: https://github.com/materialsvirtuallab/monty/issues/275.

But the new replacement returns slightly different output (an additional +00:00 at the end), which breaks strptime:

import datetime

start_time_old = datetime.datetime.utcnow()  # 2024-03-25 08:46:23.748342 

start_time_new = datetime.datetime.now(datetime.UTC)  # 2024-03-25 08:46:23.748472+00:00

print(start_time_old, start_time_new)  


dt_old = datetime.datetime.strptime(
    str(start_time_old), "%Y-%m-%d %H:%M:%S.%f"
)
print(dt_old)


dt_new = datetime.datetime.strptime(
    str(start_time_new), "%Y-%m-%d %H:%M:%S.%f"
)
print(dt_new)

Raises:

Traceback (most recent call last):
  File "/Users/yang/developer/test/test.py", line 16, in <module>
    dt = datetime.datetime.strptime(
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.12.2_1/Frameworks/Python.framework/Versions/3.12/lib/python3.12/_strptime.py", line 554, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.12.2_1/Frameworks/Python.framework/Versions/3.12/lib/python3.12/_strptime.py", line 336, in _strptime
    raise ValueError("unconverted data remains: %s" %
ValueError: unconverted data remains: +00:00