Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 3: Birthday countdown app
Lecture: Differences between dates
Login or
purchase this course
to watch this video and the rest of the course contents.
0:00
When I ran it, you can see it said compute days
0:03
actually takes no arguments but two were given.
0:05
So, we are trying to pass these parameters
0:09
but we are not accepting them in the method,
0:10
and some languages like Javascript just ignore that
0:13
but Python, if you are going to pass parameters
0:16
you have to declare that you expect them in your method.
0:20
There is actually a variety of ways to do that
0:22
we can look at that in more detail later in the class
0:24
but for now we are going to just take
0:25
what is called positional parameters
0:27
so we'll call this date1 and date2.
0:31
Ok, so date1 and date2,
0:32
we want the time between these two dates
0:35
now there is a bit of a detail that we are going to run into
0:37
so let's just do the sort of naive computation
0:40
and then we'll go back and fix it.
0:43
So what we are going to do is when you have a datetime object,
0:46
not a date object but an actual datetime object,
0:49
you can subtract one form the other, so I can say, like this,
0:54
I can say dt for change in time,
0:58
is date1 minus date2
1:01
and what we get back is what is called a time delta object,
1:04
and on here you have things like
1:06
how many hours or days or seconds
1:15
or things like that are in this time delta.
1:19
And the one we are going to work with
1:20
is actually a total seconds, ok
1:24
now total seconds is going to tell us
1:26
how many seconds there are in this entire range,
1:29
so if this was like 3 days it would be something like 210 000 seconds,
1:35
however many seconds are in days,
1:38
as opposed to just seconds,
1:40
which will only tell you sort of the seconds components
1:43
if the answer was, it's been 3 days, 2 hours and 10 seconds,
1:48
seconds here would be 10.
1:50
Seconds over here would be like 200 000.
1:53
So we can use this to actually compute
1:55
the number of days, almost, right,
1:58
there is going to be a one model fix, we've got to do,
2:00
but we can say this, we can say days equals
2:03
and then we just do super basic math,
2:05
so like 60 seconds in a minute,
2:08
and there's 60 minutes in an hour
2:10
and there is 24 hours in a day.
2:12
We can just return the days.
2:14
So, let's go down here,
2:17
and we can print out our number of days
2:21
and let's get rid of this print.
2:24
Now, this is close, if we try to run it
2:26
obviously none is not going to work
2:28
so the question is how do we get the date right now?
2:31
So we go back to our lovely datetime module
2:34
and we go to our datetime class
2:36
and there is a nice little static class method called now.
2:40
So we can call now and it will give us
2:42
a datetime object exactly now.
2:45
So this is almost going to work, let's run it.
2:49
So let's say 1974, April 1st.
2:54
All right, so how many days between now and that date?
2:58
Negative 15 000 days.
3:01
Hm, I think we did something wrong here,
3:04
and technically, this method is doing exactly what we wanted,
3:08
however, maybe we didn't name it quite exactly right,
3:13
what it really needs to do is
3:14
say assume that these dates are applying to the same year,
3:19
then how many days are between them, right,
3:21
that's really the question we are trying to answer,
3:22
because we are not wondering how many days was it
3:25
since you were born,
3:26
we are just wondering how many days this year until your birthday.
3:29
So we need to do something slightly different here.
3:32
Now the real problem is that these two dates
3:34
don't apply to the same year,
3:37
and it doesn't really matter if we say go back,
3:41
like let's assume that this one is from 1974
3:43
and this one is from 2016,
3:46
it doesn't really matter if we move that one up to 2016 or that one back,
3:51
generally it would be the same,
3:52
however, you do have to account for things like leap years
3:56
and some of these things that might make it be off by days,
3:59
so it's important for us to know which one of these
4:02
is this year and let's just update our methods here really quick.
4:07
So I'll call this original date, and we'll call this now.
4:14
So let's go over here and update this,
4:16
so we'll say date1 = now,
4:20
date2 =... Now what we need to do is create a new date,
4:24
the same year as this year but the same
4:26
day and month as the original date,
4:29
so we'll say datetime.datetime
4:32
and here we can say the year and now.year
4:35
and then original date.month, original day.day.
4:39
Excellent, so now this should be
4:43
working more like you'd expect.
4:45
Just do a quick format and run,
4:47
so 1974, April 5th, negative 34 days.
4:52
Ok, so it's like beginning of the March,
4:55
that makes perfect sense,
4:57
notice the negative and the direction
4:59
we are doing the computation
5:00
that means we are 34 days before our birthday,
5:04
so let's go down here and let's make
5:06
one quick change really quick,
5:08
let's turn this into an integer
5:10
so that throughout the whole day that it is your birthday is 0
5:12
so we could just do that by passing this decimal,
5:16
this float to the integer here,
5:19
so now let's do it one more time,
5:21
1974, 4, 1, there you go, negative 30.
5:25
Excellent, so the last thing to do
5:27
would be get rid of this print statement,
5:29
and actually print out something interesting
5:32
based on this information,
5:33
so we are passing number of days,
5:35
the parameter names don't have to match argument names obviously,
5:39
so we'll just do something really simple,
5:41
again in if statements, we'll say if days is less than 0,
5:45
that means your birthday is coming up,
5:47
so we'll do a nice little print statement,
5:48
so we'll say print your birthday is in {days} like this
5:55
and we'll do a little format,
5:57
and of course that is negative so we need to switch it
6:00
so let's proper from the users perspective,
6:02
so we'll just put a negation operation there
6:06
and then we can say else if- elif days > 0
6:10
say print you had your birthday already this year {} days ago.
6:20
Format, days like this, and then if it's not greater,
6:24
it's not less than, that means those two days were
6:27
the same days so we'll say else we'll say print,
6:31
happy birthday.
6:32
Right, let's test this out,
6:34
1974, April and say 1st, awesome,
6:39
your birthday is in 30 days.
6:41
Sounds right, let's run it again,
6:44
so 1974, let's say it was in January 15,
6:50
Oh you already had your birthday this year,
6:51
it was 47 days ago. Great, 46 days ago,
6:54
and let's test it when it's exactly the day,
6:59
yeey, it's my birthday, same date as today.
