WEBVTT

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so in this video we're going to use the
Python Library the module that we've

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installed in the previous video so
if you haven't installed pytz module you

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need to go away and do that before this
will work because otherwise you get some

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weird errors and you won't be able to
use the module so how do we check that

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that model has been installed
successfully

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well lets write up a test program to make sure it's all

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working so type....we should be able to type pytz and use it as we

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normally used an import.... so you should find

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that will work now that we have installed that and lets display the current time in moscow I am going to import date time

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as well

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and will put...

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....so we are going to display the time zone for

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moscow and we will put...

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.....

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.....and that's not actually an error
that you can see there that's just it

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showing in a different color and we will now put....

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....

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.....

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......

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...so there is our program so lets right click it and

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incidentally I've created a new Python file called tztest.py I'm still

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using the same project we've used for
date and time so right click that

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and run it so we make sure we're running
this file and the time in europe moscow

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is january 29th 2016 and its
5 am there and if you can

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just confirm that we can go to Google
and and search for current time

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moscow 5:28 a.m. GMT +3
29th of January so you can see that

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we've got that working quite nicely so
close that down now

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obviously from pytz module we used the timezone
 method on line 6 and that's because

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the pytz only deals with time zone
information by using pytz to create

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a tzinfo object then we then used on line 7 to calculate the

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local time in any country so you could
change this to any country and do the same

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now from pytz we can use the timezone
method to get the tzinfo object for any

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chosen country but the required string
is difficult to sort if you wanted to

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provide the entire list to a user so is moscow
really in Europe and will most

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people really know to look there
what we can do is we can print the

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entire list of valid strings that the
pytz.timezone method accepts

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quite easily and the reason we can do that is it
quite helpfully provides a Python list

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called all_timezones so we could put
something....

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...so run that now you can see we got a
list of everything for the various

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countries a heap of Australia as you can see but
quite a few different ones are showing there

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the other thing I actually do also is
provide a dictionary of country names

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who's keys the iso316 country code
in other words GB for britain AU for

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Australia etc so we can put...

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....

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....so if we run and have a look at the
results you can see we got the identifier to

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the left and then the actual name to the
right AU for Australia US  for United States GB for

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Great Britain etcetera now the thing to
remember here is that the list of

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countries isn't actually good enough for getting the timezone and that's because many countries

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have got more than one timezone and so it
is possible to retrieve a list of all

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the time zones for a country code and
display them after the country name so

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we might be tempted to just use the same
key then pytz.time_zone dictionary

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something like this you could do...

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......

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.....

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....so you could try that so its probably
reasonably to expect both dictionaries to

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contain the same keys so run that
we've actually got an error here so the

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program actually ran until it hit the
Key BV at which point it crashed

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and that's because there is no time zone defined for Ireland
so as its

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inhabited it's a bit strange that you have keys
 in the country names in the list at all but we

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can't really blame pytz for that

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sorry we can't really use the same keys as you
can see there now the timezone data

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itself it comes
from a data base that's maintained by

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IANA in which is the internet assigned
names authority and I'm just gonna

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bring up that link in a browser and it's
these guys and that's where the time zone

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date is coming from now it's often
referred to as the Olsen database and

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that's named after its creator Arthur David Olsen the database contains a history of

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timezone and Daylight Saving Time changes
and is pretty much considered the

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definitive source of information on
these now it is kept up-to-date and used to

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update the time zone information on most
computers although that said Windows

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does things slightly differently now
as long as your computer is receiving those updates

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the local timezone database should be
kept up to date but if you got a time for

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moscow that was four hours behind UTC
rather than 3 as you see in our pytz example

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that means your probably running Windows XP which is
no longer updated and therefore missing

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last year's change because its out of date
so with that said how to we get

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around this well we can do is go back to the
code is we can write our code a bit more

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defensively by using the Get Command
or the get method I should say and if you

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remember from the lectures on
dictionaries this returns none

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rather than an exception if the keys is not
in the dictionary so we could take a

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copy of this again well I'll just make
a change because obviously it's crashing

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the problem is is pytz.country_timezones if we change that and instead

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of putting and make the a .get
with x as the parameter that's going to return

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none in the case of there being a time
zone nonexistent for a particular

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country so you can run that and see what
happens now we don't get a crash and you

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can see we got time zones now so we come back
up Australia and you notice we got multiple time

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zones are quite happily working now
Australian Lord Howe Macquarie Hobart

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etc as we go across there is quite a
few there and likewise for some of the other ones

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as well Australia America Antarctica
etc so its obviously now working

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if you go back to B

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Bouvet Island is still showing on the list but now is not getting any
timezone information and that's

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because we got none returned and
prevented the program from crashing now if you

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needed to perform a more complicated
operation than just printing the list

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what we could do was split up the access
to country_timezones and then check if

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that the key is in the dictionary
first so

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actual what I might do is just comments one of
this out now take a copy of that but then

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ccomment that out and you can come back and refer to it if you need to so lets go back and paste that command

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again what we want to do is to start
is removing the time zones from this

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part of the

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screen here now so I'm going to...so we just got 2 we are gong to print x

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as the parameters and the format pytz.country_timezone.get(x) we are going to leave that all together

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we gonna put.....

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.....if you

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get an entry in time zone if that is the case we are going to print...

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...so this time we are actually gonna

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show that instead of just using
the default which was just to print

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anything so we can do that and run this...and you

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see we quite happily get the same
information we come up here we now got Bouvet Island

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no time zone defined and you can see its working nicely and it is a more defensive

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way of doing it and more complicated but
you can see that by splitting the access

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to country_timezone and
then checking

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the keys in the dictionary first were able to process it that way now one thing

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we might want to do is to print the
time for each of the timezones in each country

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that's fairly easy to do now that we've
got pytz to use with date time so what we gonna

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do is print each time on a new line
indented by 2 tab stops and so

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that we can remove the and parameter in the
print statement on line 12 so we gonna

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do is come up to here after the if instead of just doing a print what

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we're going to do is put....

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......

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........

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.......and I'm
going to print something a bit different

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than before and will put some tabs in
so.....

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.....

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...so no we've done
that we should be able to run this and see

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the result and you can see we've now
actually got to the actual current time

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for that time zone showing on the screen
that is pretty cool as you can see if we come

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back and check Australia we got Adelaide
current times 13:11 if I just open this

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up friday 1:11 p.m. 13:11 so that is
working nicely ok so I'm gonna end this video

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here now because it's getting a little bit long in
the next few video we're going to

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continue on our discussions and
understanding about using pytz

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and introduce you to the localize
function and to some other conversion

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that should be quite interesting for you
so we'll see you in the next video