dateutil can be installed from PyPI using pip (note that the package name is different from the importable name): Here's a snapshot, just to give an idea about the power of the package. For more ...

.../miniconda3/envs/c312/Lib/site-packages/dateutil/tz/tz.py: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated... the actually used code is 2.8.2.

When trying to make things work with the datetime module, most Python users have faced a point when we resort to guess-and-check until the errors go away. datetime is one of those APIs that seems easy ...