Convert durations to ISO8601 format (podcast episodes)

[mbertrand]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/4432

Description (What does it do?)

Converts podcast episode duration (if present) to ISO-8601 format.

How can this be tested?

• Run ./manage.py backpopulate_podcast_data
• It should complete successfully after which all published PodcastEpisode objects should have a duration that starts with "PT" or be null.

from learning_resources.models import PodcastEpisode
all_eps = PodcastEpisode.objects.filter(learning_resource__published=True)
pt_eps = all_eps.filter(duration__startswith="PT)
null_eps = all_eps.filter(duration__isnull=True)
print(all_eps.count(), pt_eps.count(), null_eps.count())
assert all_eps.count() == pt_eps.count() + null_eps.count()

>1781 1744 37

Additional Context

There are some python libraries to output durations in 8601 format (isodate, isodate2) but neither have been updated since late 2021 so I decided to roll my own function.

I placed the iso8601_duration function in etl.utils rather than etl.podcasts just in case we might want to use it for something other than podcast episodes. For example, maybe videos if we ever start ingesting them from somewhere other than Youtube (where it is already in ISO-8601 format).

[shanbady]

looks good. minor non-blocking suggestion