astimezone() cannot be applied to a naive datetime

Question

Is possible timezones() and datetimes to get conflict with my OS in terms of time etc?

This is a silly question at first, because I got this problem and I cant see why or where it is happening from.

Looking to this:

def parse_datetime(a_datetime, account):
    tz = pytz.timezone(account.timezone_name)
    return datetime.astimezone(parser.parse(a_datetime), tz)

This function simply should return a nice datetime object as timezone(), just it! But dont!

All I know is that I get this message: astimezone() cannot be applied to a naive datetime()

Since I have friends with the same function and in their PCs the code runs alright, but in my case doesnt.

Especulations are: The configuration in your machine there is something is not okay...But, not for sure.

If there is anyone else that faced this and know what it is just reading what is here, well, would be nice if you tell me, I would be glad. Thanks in advance!

Solution

You are using the wrong method to attach the timezone to the datetime object.

As documented on the pytz page you want to call that method on the datetime object, not on the class:

def parse_datetime(a_datetime, account):
    tz = pytz.timezone(account.timezone_name)
    return parser.parse(a_datetime).astimezone(tz)

This works only for already localized datetime objects (with, say, UTC as the timezone).

As the same documentation points out, you are better of using the .localize() method on the timezone object:

def parse_datetime(a_datetime, account):
    tz = pytz.timezone(account.timezone_name)
    return tz.localize(parser.parse(a_datetime))

This works on naive datetime objects, and does the correct thing for timezones with historical data too.

If you have mixed data, some with and some without timezones, then you should test for the timezone already being there:

def parse_datetime(a_datetime, account):
    dt = parser.parse(a_datetime)
    if dt.tzinfo is None:
        tz = pytz.timezone(account.timezone_name)
        dt = tz.localize(dt)
    return dt

Timestamps that already have a timezone attached will result in timezone-aware datetime objects and don't need to recast into another timezone.

Comments

[R.R.C.]

I changed the code as you showed, but it still giving: astimezone() cannot be applied to a naive datetime

[R.R.C.]

@MartijinPieters, I'm really glad you're helping me with this, but this case is pretty strange. Something is really related to my PC idk! The return of the function is this: 2013-11-01T23:00:00+00:00 You can see at the end 00+00:00 (It should not be that way).

[Martijn Pieters]

@Doug: That is the string representation of a datetime object. it is working fine.

[R.R.C.]

Following the last modification in the code, it got the same ExceptionType: ValueError, and the message now changed to: Not naive datetime (tzinfo is already set)

[Martijn Pieters]

@Doug: Some of your input has a timezone as part of the parsed string then.