1
00:00:00,330 --> 00:00:07,980
Let's talk about something that's quite unique to Python and makes things really really nice as Python

2
00:00:07,980 --> 00:00:08,760
programmers.

3
00:00:08,850 --> 00:00:13,870
And it's called comprehension is it's one of our key terms comprehension.

4
00:00:13,890 --> 00:00:15,330
What are they.

5
00:00:15,330 --> 00:00:25,520
Well they're actually called list comprehension for set comprehension or dictionary comprehension.

6
00:00:25,560 --> 00:00:32,970
And these are some of the data types that we have in Python and we're able to use all comprehension

7
00:00:33,540 --> 00:00:37,860
with these three data types by the way as I'm recording.

8
00:00:37,860 --> 00:00:40,890
There are some birds chirping in the background.

9
00:00:41,010 --> 00:00:44,320
I thought it would be nice to just record the birds chirping in the background.

10
00:00:44,340 --> 00:00:47,400
I think it would be peaceful for you if you get annoyed.

11
00:00:47,400 --> 00:00:51,020
I'm sorry but hey the birds have to have fun as well.

12
00:00:51,060 --> 00:00:51,330
OK.

13
00:00:51,520 --> 00:00:54,310
So what are these comprehension.

14
00:00:54,870 --> 00:01:05,250
Well they're a quick way for us to create lists or sets or dictionary in Python instead of perhaps looping

15
00:01:05,880 --> 00:01:14,560
or appending to a bunch of items to lists so let me show you instead of doing something like my list

16
00:01:14,800 --> 00:01:17,590
equals an empty list.

17
00:01:17,590 --> 00:01:22,720
And from here I'll do something like For character in Hello

18
00:01:25,320 --> 00:01:28,200
my list dot append

19
00:01:31,200 --> 00:01:35,410
character just so I can create this list finally.

20
00:01:35,580 --> 00:01:38,370
So let's say my list and we'll print this out

21
00:01:41,560 --> 00:01:50,350
if I click Run I created a list that contains the characters from hello all right.

22
00:01:50,370 --> 00:01:54,500
But is there a faster cleaner way of doing this.

23
00:01:54,700 --> 00:01:58,450
And yes there is with list comprehension and python.

24
00:01:58,510 --> 00:02:00,760
Again it is quite unique.

25
00:02:00,850 --> 00:02:07,270
You don't see it in a lot of programming languages but people that use python really love this feature

26
00:02:07,750 --> 00:02:09,480
and I do too.

27
00:02:09,490 --> 00:02:17,490
So how can we do this using a list comprehension Well the format we're going to follow is like this

28
00:02:18,620 --> 00:02:32,920
we're going to say param for param in it of all so when I say param I mean parameter or in our case

29
00:02:32,920 --> 00:02:36,130
it could be a variable so we can name it whatever we want.

30
00:02:36,130 --> 00:02:42,940
So let's name this character like we did in here and then character like we did in here and then we

31
00:02:42,940 --> 00:02:44,500
want an editable.

32
00:02:44,500 --> 00:02:54,870
In our case we'll say hello so that if I remove this and I click Run I get the same thing.

33
00:02:54,970 --> 00:02:56,280
Just like that.

34
00:02:56,320 --> 00:03:07,150
So upon creation online three I create a list that contains character and hello I do a for loop in here

35
00:03:07,660 --> 00:03:14,100
and I create the list so the way that I like to think about it is hey create a variable and then we're

36
00:03:14,100 --> 00:03:25,340
going to do a for loop saying hey for each variable in the ignorable added to the list okay let's expand

37
00:03:25,340 --> 00:03:31,040
upon this Let's say I wanted to do something else let's call it my list too.

38
00:03:31,430 --> 00:03:40,850
And I want to create let's say a quick list with numbers ranging from zero to 100 0 0 to ninety nine.

39
00:03:40,850 --> 00:03:44,610
How would I go about doing this again using list comprehension.

40
00:03:44,630 --> 00:03:47,330
I'll say Number Four.

41
00:03:47,330 --> 00:03:48,090
Number.

42
00:03:48,290 --> 00:03:49,680
And then what's the later rule.

43
00:03:49,730 --> 00:03:50,730
I'm going to use.

44
00:03:50,780 --> 00:03:59,960
Well I'm going to use a range and say zero to 100 hundred so that if I click Run here look that I get

45
00:03:59,960 --> 00:04:04,040
a nice long list pre populate it with all these numbers.

46
00:04:04,130 --> 00:04:07,250
How cool is that okay.

47
00:04:08,270 --> 00:04:10,030
But here's my challenge to you.

48
00:04:10,190 --> 00:04:15,690
What if I wanted this but all the numbers should be multiplied by two.

49
00:04:15,920 --> 00:04:18,130
So I want a list where this equals to zero.

50
00:04:18,140 --> 00:04:18,970
This is two.

51
00:04:18,970 --> 00:04:20,180
This is four.

52
00:04:20,240 --> 00:04:21,110
This is six.

53
00:04:21,110 --> 00:04:21,890
This is eight.

54
00:04:21,890 --> 00:04:22,990
This is 10.

55
00:04:23,030 --> 00:04:24,750
So on and so forth.

56
00:04:24,830 --> 00:04:25,550
How can I do it.

57
00:04:26,830 --> 00:04:36,220
Well we can actually expand upon this so that my list three this time around we'll use the same for

58
00:04:36,220 --> 00:04:44,840
loop that we've seen before like this but instead of just the variable this is not an expression of

59
00:04:44,840 --> 00:04:51,730
how we want to act upon each character just like we saw in lambda expressions.

60
00:04:52,160 --> 00:05:00,020
So I can now say Num Times to for these items.

61
00:05:00,150 --> 00:05:06,460
So now if I do my last three Hey check that out.

62
00:05:06,530 --> 00:05:08,770
That's pretty nice isn't it.

63
00:05:08,990 --> 00:05:12,940
OK let's make it even more challenging.

64
00:05:12,950 --> 00:05:15,120
Let's say my list three.

65
00:05:15,340 --> 00:05:25,400
Now let's make this a little bit bigger here my list for I want to change it so that in my list I still

66
00:05:25,400 --> 00:05:33,670
keep here what I have the numbers but I want to only keep that even numbers in this case.

67
00:05:33,690 --> 00:05:35,880
All of them are even because they're multiplied by two.

68
00:05:36,270 --> 00:05:44,180
But if for example we do to the power of two and let's comment this out for a second and click Run we

69
00:05:44,180 --> 00:05:51,900
see that some numbers aren't even so I want to keep these numbers but only the even ones.

70
00:05:52,250 --> 00:05:56,600
How would I go about doing it well in this case.

71
00:05:56,600 --> 00:05:59,900
We have a new way of creating this list expression.

72
00:05:59,990 --> 00:06:02,350
We'll do the exact same thing that we've done here.

73
00:06:02,360 --> 00:06:10,870
So I'm just going to copy that but at the end remember we now have an expression here something that

74
00:06:10,870 --> 00:06:19,130
we're going to do to effect whatever the item in the editable is we're going to loop through things.

75
00:06:19,130 --> 00:06:28,220
And then finally after this we can say f or we can do an if condition so let's say in our case I'll

76
00:06:28,220 --> 00:06:34,780
say if num modulo 2 is equal to zero.

77
00:06:34,780 --> 00:06:45,250
Only then added to the list so if we click run well and make sure that it's less for click Run look

78
00:06:45,250 --> 00:06:45,880
at that.

79
00:06:45,910 --> 00:06:48,380
All of these are even numbers.

80
00:06:48,460 --> 00:06:49,860
So let's look at this format.

81
00:06:51,830 --> 00:06:56,280
Remember these are called list comprehension.

82
00:06:56,350 --> 00:07:03,250
It's a way for us to quickly create lists with Python instead of looping and using append or things

83
00:07:03,250 --> 00:07:12,210
that we've seen before so it's a shorthand form for us to do things unique like this the way we're able

84
00:07:12,210 --> 00:07:20,520
to do this is to have an expression here of what we want to do with each item that we're iterating over

85
00:07:21,360 --> 00:07:26,860
we loop using a for loop through an admirable.

86
00:07:26,940 --> 00:07:30,190
We give it to a variable which we're going to act upon.

87
00:07:30,330 --> 00:07:40,140
And then if we want we also have an option to add a conditional and say hey only included into the list

88
00:07:40,200 --> 00:07:47,350
based on this condition based on a true or false very very cool.

89
00:07:47,460 --> 00:07:53,750
Now although list comprehension are really nice because they're just simple one liners.

90
00:07:54,090 --> 00:07:58,140
It can get pretty confusing looking at this code.

91
00:07:58,290 --> 00:08:03,320
You have to be really familiar with less comprehension to really understand what's going on.

92
00:08:03,330 --> 00:08:11,760
So although this makes code shorter maybe even cleaner it does take away a bit of its readability so

93
00:08:11,760 --> 00:08:21,210
it might be better to just create a descriptive function like generate list of even numbers or something

94
00:08:21,210 --> 00:08:22,990
along those lines.

95
00:08:23,220 --> 00:08:24,810
So it's more descriptive.

96
00:08:24,930 --> 00:08:28,920
And another developer might have a better idea of what's going on.

97
00:08:28,920 --> 00:08:31,380
So it's always a tradeoff.

98
00:08:31,480 --> 00:08:37,030
Let's take a break and talk about set and dictionary comprehension in the next video by.