Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
Let's use the `pytz` library instead of the timezones in `datetime`.
Format string
fmt = '%Y-%m-%d %H:%M:%S %Z%z'
Links
pytzdocs-
More about
pytzfrom SaltyCrane
Libraries
To make time zones better we're gonna be
using library named pytz.
0:00
We've already installed it for you on
Workspaces, but
0:03
you'll need to install it yourself
locally.
0:06
You can do this with pip install pytz.
0:08
All right, let's see how this tool works.
0:12
All right, we're going to need our date
time libraries.
0:14
So we have all that imported.
0:17
And we're also gonna be using pytz as we
talked about.
0:18
So we have that imported as well.
0:21
All right, so pytz I really recommend you
go look at the docs for
0:24
it, it has a whole lot of stuff that makes
all this work so much easier.
0:29
So, in our last video, we did Eastern and
Pacific by specifying time deltas.
0:33
Well, let's do those again.
0:38
We'll do Pacific first and [SOUND] we're
gonna do the pytz method.
0:39
And so we actually specify the name of the
time zone.
0:45
So, for instance, we want the US Pacific
time zone,
0:51
we specify US Pacific and if we do
Eastern, [SOUND] US Eastern.
0:56
Okay.
1:01
So now we have those, great.
1:02
Now let's use let's give ourselves this
format string.
1:04
We're gonna use this a lot so we're just
gonna go ahead and put this in here.
1:07
So, this should be familiar.
1:11
[BLANK_AUDIO]
1:13
All right so, year, month, day, hour,
minute, second, and
1:16
then we're gonna do cap Z and lowercase z,
and so what do these two do?
1:20
Well cap Z gives us the time zone name so
Pacific or
1:25
India standard time or whatever.
1:28
And the lowercase z prints out the offset
of that timezone from UTC.
1:31
So we'd get like minus 8, or plus 550, or,
or whatever.
1:36
Speaking of UTC, let's make a variable
that holds onto UTC.
1:41
You can actually just do pytz.utc.
1:46
We're only saving five characters, but,
you know, I get lazy as a programmer.
1:49
So let's make a date time in the Pacific
time zone,
1:54
with the one that we've been doing, all
right?
1:57
Pacific.localize, datetime.datetime,
2:01
2014, 4, 21, 9.
2:07
[BLANK_AUDIO]
2:11
So what's the pacific.localize?
2:12
Well what that does is it takes a naive
date time or
2:14
it can work with aware ones too, I do
believe.
2:18
But anyway, it takes a date time and gives
it to you with a certain time zone.
2:23
So if we do start.strftime with our format
string, then there we go.
2:26
We've got Pacific daylight time at 7 hours
ahead.
2:32
And we've got our date and our time.
2:35
'Kay, so that's awesome.
2:38
We can see from our usual info here that
it's in the Pacific time zone, and let's,
2:39
let's do what we did before and let's try
turning this into an Eastern time zone.
2:44
So let's call this start_eastern.
2:48
[SOUND] And we're gonna go back to using
that as time zone.
2:51
So now if I look at start_eastern, I get
this new one and we can see that it is,
2:57
[SOUND] well let's look at start.
3:02
So we can see these two here, right?
3:04
So we've got PDT and EDT.
3:05
And we've got our correct times.
3:08
So that's great.
3:10
But why did we use this as time zone
instead of using localize again?
3:12
Well, localize is for naive date times.
3:15
And since our start variable was already
time zone aware, it's no longer naive.
3:18
We can't localize it again.
3:22
Most of the time, though, you're gonna
wanna work with times in UTC.
3:24
And you're gonna convert them when they
get put out, right,
3:28
when they go out to a local time.
3:31
So, let's see about how we would do that.
3:32
So, let's do a start utc,
3:34
datetime.datetime, [SOUND] 2014,
3:38
4, 21, 1 and tz is gonna be utc.
3:43
So now, if I start_utc and put in my
format string, then, we get that, right?
3:48
UTC is plus 0, that's exactly where we
wanna be.
3:53
Okay.
So now,
3:56
let's convert this back to Pacific.
3:57
So start utc.astimezone, [SOUND] and
3:59
now let's look at start_pacific.
4:03
And there we go, so that's 18 o'clock or
rather 6 o'clock.
4:08
And we're in our Pacific time zone.
4:12
If it's always best to work in UTC, how do
we do this in the real world?
4:15
Well, we need to know where the data's
coming from.
4:20
To illustrate this, let's let's add
another couple of time zones to our mix.
4:23
We're gonna use our friends Auckland and
Mumbai again.
4:26
So Auckland will be pytz.timezone,
Pacific/Auckland.
4:29
So don't get US Pacific and
Pacific/Auckland mixed up.
4:36
And Mumbai will be [SOUND] Asia/Calcutta.
4:39
It's like I said, all of India is in the
same timezone, so
4:47
we can just use Calcutta instead of trying
to find Mumbai or whatever.
4:50
Let's make a new time zone, and we're
gonna make it here local in US time.
4:55
So, let's do apollo_13_naive.
5:00
[SOUND] So, this is when, Apollo 13
launched,
5:04
which is 1970, on April 11, at 14,
5:10
13 UTC time, sort of, all right?
5:15
So we're starting this as this local date
time.
5:20
So we, we have this time.
5:23
Sorry, and we wanna convert this to
Eastern, so
5:26
apollo_13_eastern will be
Eastern.localize, apollo_13_naive.
5:30
Okay, so if we look at apollo_13_naive,
and
5:39
apollo _13_eastern, we have the same time.
5:44
Because that's, that was when it was
launched.
5:49
Right?
Two in the afternoon.
5:51
'Kay, so there's our eastern version.
5:52
Now, like I said,
5:54
we should be starting this as UTC for all
of our around the world conversions.
5:55
So why do we wanna store it as UTC?
5:59
Well, it's because UTC doesn't deal with
daylight saving times.
6:01
So, converting into and out of DST isn't
as hard
6:05
as it is if you have to remember whether
or not the original time is in DST.
6:08
If you'll going to [UNKNOWN], like fewer
calculations have to worry about.
6:12
Not to mention the fact that some
countries go in to DST at different times
6:16
from other countries that are even in the
same time zone.
6:19
Watch that video, time zones are
ridiculous.
6:22
Okay.
6:25
So, let's make apollo_13_utc.
6:26
So we're going to do
apollo_13_eastern.astimezone, utc.
6:29
So why do we start with apollo_13_eastern
instead of apollo_13_naive?
6:37
Well naive doesn't know where it is,
6:41
so it doesn't know how to convert itself
into UTC.
6:42
That's why we wanna start with Eastern.
6:44
That's quite a few steps just to get to
having this UTC time.
6:47
But, now, we can find this time all over
the world.
6:52
So let's see when Apollo 13 launched in
the Pacific.
6:55
[SOUND] So it launched at 11:13.
7:01
Okay, cool.
7:08
When did it do that in Auckland?
7:10
[SOUND] It was the next day at seven in
the morning.
7:12
Okay.
7:17
When did it do it in Mumbai?
7:18
[SOUND] That was the next day and it was
right after midnight,
7:21
43 minutes after midnight.
7:27
So, so long as you start with UTC dates
and times,
7:30
you can always generate new dates and
times for
7:33
anywhere in the world without worrying
about getting incorrect dates and times.
7:35
Your Tardis wants to work on UTC times.
7:40
Right?
7:43
Your Tardis will be able to get you where
you wanna go as long as you
7:44
start with UTC.
7:46
But, wait a minute.
7:47
What if you don't know all of the time
zones?
7:48
So, pytz actually has two really handy
little bits for finding time zones.
7:51
There is pytz.alltimezones.
7:55
And this lists all the time zones,
8:00
which is this, this huge, huge list of
time zones.
8:02
Or you can do pytz.country_timezones.
8:05
And you can pass in a country two letter
code.
8:10
And you get back just the time zones for
that country.
8:13
So you can see we've got all of our usual
ones.
8:17
We've got some crazy ones in like, Indiana
and North Dakota, and
8:20
then we've got some in like, Alaska.
8:24
All right.
8:26
That's pretty much it for pytz for right
now.
8:27
Hopefully, pytz gives you some more
confidence when working with times and
8:32
dates in Python.
8:35
There are some other great libraries out
there for
8:36
working with this often confusing data
that I'll link to in the teacher's notes.
8:38
Before our last video, use the pytz and
date time documentation to build a script
8:42
that takes a date and time in your time
zone, and then gives that time back
8:47
in six other time zones using our format
string from this video.
8:51
I'll show you my solution in the next
video,
8:55
and the format string is in the teacher's
notes.
8:56
You need to sign up for Treehouse in order to download course files.
Sign up