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Chris White
6,212 PointsStuck with Python timezone issue
I think half the problem is I'm not entirely sure what the end result it's expecting is - weather to use a pytz. notation approach or the .astimezone() approach (maybe neither?). But I'm stuck on this:
Create a function named to_timezone that takes a timezone name as a string. Convert starter to that timezone using pytz's timezones and return the new datetime.
Here's what I've got, which is obviously incorrect, and I've been stuck here for a few days:
import datetime
import pytz
starter = pytz.utc.localize(datetime.datetime(2015, 10, 21, 23, 29))
def to_timezone(new_timezone):
starter.astimezone(new_timezone)
return starter
1 Answer
Chris Freeman
Treehouse Moderator 68,423 PointsThe Timezone Strings Challenge asks:
Create a function named to_timezone that takes a timezone name as a string. Convert starter to that timezone using pytz's timezones and return the new datetime.
The function will need to do three things: create a new timezone, create a new datetime object based on starter, and return the new datetime object. Here is one solution:
import datetime
import pytz
starter = pytz.utc.localize(datetime.datetime(2015, 10, 21, 23, 29))
def to_timezone(new_timezone):
# generate timezone from string
new_tz = pytz.timezone(new_timezone)
# convert starter to new datetime
new_dt = starter.astimezone(new_tz)
# Return new datetime object
return new_dt
The last two statement could be combined and return the new datetime directly:
# Return new datetime object
return starter.astimezone(new_tz)
Of if you insist on approaching unreadable, you could do:
def to_timezone(new_timezone):
return starter.astimezone( pytz.timezone(new_timezone) )
Chris White
6,212 PointsThanks, that did the trick, and reading it makes total sense.
I'll really need to go back at some point and spend a lot more time here. Very frustrating stuff.
But a quick question: Why wouldn't it (or would it?) work to just skip creating new_dt and plug in the argument straight into the .astimezone part? If we assume the string is a timezone, why wouldn't it work to just say:
return starter.astimezone(string)?
Chris Freeman
Treehouse Moderator 68,423 PointsChris White: While going straight to return starter.astimezone(string) looks inviting, it definately will not work! Coding would be a breeze if it did. Why? it's all about type.
Functions expect parameters of a specific object type: integer (int), string ('str'), etc. Some functions take other functions (as callable object) as parameters!
The function pytz.timezone() expects a string parameter and returns a timezone object. Whereas, starter is a "timzone aware" datetime object with an astimezone() method which expects a timezone object and returns and updated datetime object. Say THAT 10 times fast!
If you're unsure what is being produced by a statement, you can inspect the output using type() and dir(). Doing this on the above code yields this:
In [229]: import pytz
In [230]: import datetime
In [231]: starter = pytz.utc.localize(datetime.datetime(2015, 10, 21, 23, 29))
In [232]: new_tz = pytz.timezone('US/Eastern')
In [233]: type(new_tz)
Out[233]: pytz.tzfile.US/Eastern
In [234]: dir(new_tz)
Out[234]:
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_dst', '_transition_info', '_tzinfos', '_tzname', '_utc_transition_times', '_utcoffset', 'dst', 'fromutc', 'localize', 'normalize', 'tzname', 'utcoffset', 'zone']
In [235]: new_dt = starter.astimezone(new_tz)
In [236]: type(new_dt)
Out[236]: datetime.datetime
In [237]: dir(new_dt)
Out[237]:
['__add__', '__class__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__ne__', '__new__', '__radd__', '__reduce__', '__reduce_ex__', '__repr__', '__rsub__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', 'astimezone', 'combine', 'ctime', 'date', 'day', 'dst', 'fromordinal', 'fromtimestamp', 'hour', 'isocalendar', 'isoformat', 'isoweekday', 'max', 'microsecond', 'min', 'minute', 'month', 'now', 'replace', 'resolution', 'second', 'strftime', 'strptime', 'time', 'timetuple', 'timetz', 'today', 'toordinal', 'tzinfo', 'tzname', 'utcfromtimestamp', 'utcnow', 'utcoffset', 'utctimetuple', 'weekday', 'year']
For grins, let's try calling starter.astimezone() with a string argument:
In [238]: starter.astimezone('US/Eastern')
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-238-d536f300de46> in <module>()
----> 1 starter.astimezone('US/Eastern')
TypeError: astimezone() argument 1 must be datetime.tzinfo, not str
As you can see, the astimezone() method does not care for a string input.
Robert Richey
Courses Plus Student 16,352 PointsRobert Richey
Courses Plus Student 16,352 PointsHi Chris,
Just fixed the formatting to help make it more readable. I haven't yet gotten to this step in Python, but I'm not far behind. I'll keep an eye on this thread and when I reach a point I can answer it, I'll do so if no one else has. This could take days - because, learning timezones is like running through mud for me.