1
00:00:01,140 --> 00:00:02,580
Narrator: So up until now,

2
00:00:02,580 --> 00:00:07,500
we learned that strings can be accessed quite easily.

3
00:00:07,500 --> 00:00:09,210
And using the square brackets,

4
00:00:09,210 --> 00:00:12,300
we can access different parts of the string.

5
00:00:12,300 --> 00:00:14,570
And this idea of a start,

6
00:00:14,570 --> 00:00:16,200
a stop,

7
00:00:16,200 --> 00:00:18,366
and a step over

8
00:00:18,366 --> 00:00:22,140
is what we call slicing or string slicing,

9
00:00:22,140 --> 00:00:25,653
because we can slice the string however we like.

10
00:00:26,490 --> 00:00:29,040
But we also need to learn another important term

11
00:00:29,040 --> 00:00:32,159
that's gonna come up again and again throughout this course.

12
00:00:32,159 --> 00:00:34,403
And as a matter of fact, it's an important concept that

13
00:00:34,403 --> 00:00:37,200
as you get more advanced into programming,

14
00:00:37,200 --> 00:00:39,390
you really need to understand.

15
00:00:39,390 --> 00:00:41,280
what is this concept?

16
00:00:41,280 --> 00:00:44,700
Well, it's this idea of immutability.

17
00:00:44,700 --> 00:00:47,403
It's an important term in programming.

18
00:00:48,630 --> 00:00:51,513
What does immutability mean?

19
00:00:52,560 --> 00:00:55,500
Well, strings in Python are immutable.

20
00:00:55,500 --> 00:00:58,320
That means they cannot be changed.

21
00:00:58,320 --> 00:01:00,300
What do I mean by that?

22
00:01:00,300 --> 00:01:04,590
Now that we've assigned selfish this value

23
00:01:04,590 --> 00:01:06,540
this string,

24
00:01:06,540 --> 00:01:07,650
well...

25
00:01:07,650 --> 00:01:09,450
I can reassign it, right?

26
00:01:09,450 --> 00:01:11,733
I can say selfish is 100 now,

27
00:01:12,685 --> 00:01:15,460
and if I print selfish

28
00:01:17,076 --> 00:01:20,550
and I click run, that works.

29
00:01:20,550 --> 00:01:23,880
But if I instead do something like

30
00:01:23,880 --> 00:01:28,880
the first index of selfish is going to equal eight,

31
00:01:29,400 --> 00:01:30,820
and I click run

32
00:01:31,830 --> 00:01:32,808
I get an error.

33
00:01:32,808 --> 00:01:34,500
I get a type error saying,

34
00:01:34,500 --> 00:01:37,863
String object does not support item assignment.

35
00:01:38,790 --> 00:01:39,960
Why is that?

36
00:01:39,960 --> 00:01:42,483
Because strings are immutable.

37
00:01:43,320 --> 00:01:45,776
That is, I cannot change

38
00:01:45,776 --> 00:01:47,640
the value of this

39
00:01:47,640 --> 00:01:49,023
once it's created.

40
00:01:50,160 --> 00:01:54,030
I can't just immediately change it to 8, 1-2-3-4-5-6-7.

41
00:01:54,030 --> 00:01:56,490
Nope, it has to stay the same.

42
00:01:56,490 --> 00:02:00,330
The only way that I can remove this or change this

43
00:02:00,330 --> 00:02:03,183
is to completely reassign the value.

44
00:02:04,800 --> 00:02:06,639
So that in memory,

45
00:02:06,639 --> 00:02:10,949
Python removes all of this from our bookshelf of memory

46
00:02:10,949 --> 00:02:15,570
and instead just assigns eight into the zero bookshelf

47
00:02:15,570 --> 00:02:18,570
and removes everything else because we don't use it anymore.

48
00:02:19,860 --> 00:02:22,572
Now, this idea of immutability

49
00:02:22,572 --> 00:02:25,169
is something we'll explore more and more,

50
00:02:25,169 --> 00:02:28,530
especially when we start talking about lists.

51
00:02:28,530 --> 00:02:30,300
But for now, just remember

52
00:02:30,300 --> 00:02:34,590
that you can't reassign part of a string.

53
00:02:34,590 --> 00:02:38,730
Once created, it exists like that in that form.

54
00:02:38,730 --> 00:02:42,720
The only way we can change it is to create something new.

55
00:02:42,720 --> 00:02:46,500
We can do selfish plus eight,

56
00:02:46,500 --> 00:02:48,930
and we can create it that way.

57
00:02:48,930 --> 00:02:53,370
But now this selfish is a whole new string.

58
00:02:53,370 --> 00:02:56,490
This no longer exists,

59
00:02:56,490 --> 00:03:00,060
and a whole new shelf space was created

60
00:03:00,060 --> 00:03:02,613
for us to use this whole new string.

61
00:03:03,870 --> 00:03:06,390
Again, if this doesn't make sense to you

62
00:03:06,390 --> 00:03:09,034
or why it's important just yet, don't worry.

63
00:03:09,034 --> 00:03:10,530
We'll get there.

64
00:03:10,530 --> 00:03:12,810
For now though, I'll see you in the next video.

65
00:03:12,810 --> 00:03:13,643
Bye bye.