How to check if a datetime object is localized with pytz?

if you want to check if a datetime object 'd' is localized, check the d.tzinfo, if it is None, no localization.

How do I determine if localization is needed?

From datetime docs:

• a datetime object d is aware iff:

  d.tzinfo is not None and d.tzinfo.utcoffset(d) is not None
  

• d is naive iff:

  d.tzinfo is None or d.tzinfo.utcoffset(d) is None
  

Though if d is a datetime object representing time in UTC timezone then you could use in both cases:

self.date = d.replace(tzinfo=pytz.utc)

It works regardless d is timezone-aware or naive.

Note: don't use datetime.replace() method with a timezone with a non-fixed utc offset (it is ok to use it with UTC timezone but otherwise you should use tz.localize() method).

Here is a function wrapping up the top answer.

def tz_aware(dt):
    return dt.tzinfo is not None and dt.tzinfo.utcoffset(dt) is not None