1
00:00:12,040 --> 00:00:14,450
Hi, everybody, welcome to the lecture.

2
00:00:15,190 --> 00:00:20,560
We're going to start off with a new topic and we're going to discuss exceptions and errors in the code

3
00:00:21,460 --> 00:00:24,940
once we have completed the challenging part of OLP.

4
00:00:25,300 --> 00:00:29,810
Now it's time to know how to handle exceptions and errors in our code.

5
00:00:30,160 --> 00:00:35,560
In a perfect world, a programmer would create a piece of code that will run perfectly and would not

6
00:00:35,560 --> 00:00:37,390
have any fair points or errors.

7
00:00:37,780 --> 00:00:44,860
But in the real world, in real programming projects, as they grow, they have more and more potential

8
00:00:44,860 --> 00:00:46,990
to have exceptions and errors in them.

9
00:00:47,890 --> 00:00:55,270
And we better know we better be prepared to handle them and not leave it to luck and hope that we would

10
00:00:55,270 --> 00:00:56,640
not have these errors.

11
00:00:57,490 --> 00:01:05,380
We would need to have a sort of prediction ability to know how to catch these errors or even fix them

12
00:01:05,380 --> 00:01:07,300
in the code once we encounter them.

13
00:01:09,570 --> 00:01:17,310
In computer science are once the program encounters an error, it is called an exception.

14
00:01:18,510 --> 00:01:18,960
All right.

15
00:01:18,960 --> 00:01:23,190
So let's go with the slides here and see the following examples.

16
00:01:23,560 --> 00:01:29,400
An exception would happen once a program is executed and it would encounter a wrong piece of code.

17
00:01:30,120 --> 00:01:37,080
By the way, it can come in many ways and shapes and we have many types of errors and we will go over

18
00:01:37,320 --> 00:01:39,660
the common ones in a few minutes.

19
00:01:41,070 --> 00:01:49,620
So when the code execution encounters the wrong piece of code, it will cause the code to fail at that

20
00:01:49,620 --> 00:01:50,100
point.

21
00:01:50,130 --> 00:01:56,790
Python does not know what to do with the defective code, and it basically terminates the execution

22
00:01:56,790 --> 00:01:57,540
on the spot.

23
00:01:59,140 --> 00:02:07,750
Biden also knows exactly what type of exception is thrown once it happens, and then we can apply certain

24
00:02:07,750 --> 00:02:17,350
actions to either get a flow of code, to do something, to do some commands or either to fix the code.

25
00:02:19,210 --> 00:02:27,820
So how do we know that our code is failing and that we had an exception, so once we run a certain Python

26
00:02:27,820 --> 00:02:32,340
file and the code will encounter an exception, the run will stop.

27
00:02:32,530 --> 00:02:41,710
So by the look of our picture, if we're looking at our code stopped in the middle, it's probably because

28
00:02:41,710 --> 00:02:45,010
we had an exception during the run.

29
00:02:45,250 --> 00:02:52,990
If the code flow will encounter a badly written code, it will cause the run to fail and the error would

30
00:02:52,990 --> 00:02:56,600
be displayed at the terminal log off by chance in red color.

31
00:02:56,950 --> 00:03:06,300
So once we are executing a code and we will encounter a certain exception, it will be printed for us

32
00:03:06,310 --> 00:03:08,650
so we could read and debug it.

33
00:03:08,650 --> 00:03:16,180
And to understand what that means, the terminal would also give us indication and what class method

34
00:03:16,180 --> 00:03:23,890
or module the exception happened and also would point us to the exact line in the code so we could look

35
00:03:23,890 --> 00:03:26,320
at that problematic line and fix it.

36
00:03:28,140 --> 00:03:36,120
So once we are familiar with, like, what are the signs that we had an exception and where can we find

37
00:03:36,120 --> 00:03:40,890
and read that exception, let's see a list of exceptions.

38
00:03:41,070 --> 00:03:45,360
And I picked up the popular ones because there are many of them.

39
00:03:45,360 --> 00:03:52,560
And covering all the exceptions is irrelevant, because once you get the idea of what is an exception,

40
00:03:52,860 --> 00:03:59,420
even if you will encounter is some exception that you're not familiar with, you could go to Google,

41
00:03:59,430 --> 00:04:01,100
read about it and learn more.

42
00:04:01,800 --> 00:04:04,320
But we're going to talk about the common ones.

43
00:04:04,440 --> 00:04:08,240
I picked that up for you and you will see some examples as well.

44
00:04:08,670 --> 00:04:10,560
So let's begin first.

45
00:04:10,560 --> 00:04:13,200
One is syntax error or parsing error.

46
00:04:13,680 --> 00:04:20,760
This error will because once the code will encounter a programmatic logic of failure or once we will

47
00:04:20,760 --> 00:04:30,390
not fall to Python syntax rules for the example of that syntax error or parsing like the come as a power

48
00:04:31,020 --> 00:04:31,890
you can see here.

49
00:04:31,890 --> 00:04:35,340
And if statement if A is below, then three.

50
00:04:35,670 --> 00:04:41,060
But it was caused because we did not put any value in a OK.

51
00:04:41,130 --> 00:04:44,940
We did not declare the variable before using it.

52
00:04:45,210 --> 00:04:48,810
So the terminal would give us this exception right here.

53
00:04:49,050 --> 00:04:56,910
And we could see here that it happened in this file, Eurhythmics exception UI.

54
00:04:58,200 --> 00:05:01,700
And you can see here that if you would click on it.

55
00:05:02,070 --> 00:05:06,990
So first of all, we know the name of the file and we have also indication what line happened.

56
00:05:06,990 --> 00:05:07,710
Line one.

57
00:05:09,130 --> 00:05:15,420
And also, we have a small error pointing up here, pointing us to where exactly the exception happened.

58
00:05:15,430 --> 00:05:22,270
So it's basically here in the statement of values and also we have the exception itself, syntax error.

59
00:05:30,000 --> 00:05:34,390
Right here, and we need to fix it, so this is for syntax error.

60
00:05:34,890 --> 00:05:39,220
Let's see the second example of zero division error.

61
00:05:39,570 --> 00:05:41,390
OK, the name speaks for itself.

62
00:05:41,700 --> 00:05:48,390
Basically, we are getting this exception once we're doing an illegal mathematical action, which is

63
00:05:48,570 --> 00:05:50,800
dividing a certain number by zero.

64
00:05:51,090 --> 00:05:56,180
So in the real world, regardless of programming, you cannot divide anything by zero.

65
00:05:56,370 --> 00:05:58,010
It's an illegal math action.

66
00:05:58,260 --> 00:06:03,510
So Python will tell us that zero division error division by zero.

67
00:06:03,540 --> 00:06:05,690
OK, so this is also an exception.

68
00:06:05,970 --> 00:06:09,240
This will cause our code stop running.

69
00:06:09,430 --> 00:06:15,000
So if we have these two lines and then we have a hundred more lines, the code will stop here.

70
00:06:17,290 --> 00:06:25,090
Third one in line is tie power, and it will occur once using a wrong type of object and it can appear

71
00:06:25,090 --> 00:06:27,670
in many scenarios, I just gave you a one here.

72
00:06:28,540 --> 00:06:32,050
We already encountered this scenario many times.

73
00:06:32,050 --> 00:06:39,190
In the course we have here, X equals five, and then we're trying to print a string together with an

74
00:06:39,190 --> 00:06:39,780
integer.

75
00:06:39,940 --> 00:06:49,960
And this would cause us the type error you can see here can only concatenate string nuttiness to string.

76
00:06:51,040 --> 00:06:56,380
And also pointing out here the line and also pointing out the name of the file.

77
00:06:58,360 --> 00:07:00,290
So how can we fix it?

78
00:07:00,630 --> 00:07:02,290
We already did it many times.

79
00:07:02,530 --> 00:07:06,510
We should fix it by using casting in that order.

80
00:07:09,400 --> 00:07:17,200
All right, fourth in line, name error name is caused when a variable cannot be found in local or global

81
00:07:17,200 --> 00:07:17,710
scope.

82
00:07:17,980 --> 00:07:25,900
So here we have a math accident, X plus five, but we never created X, so Python does not know what

83
00:07:25,900 --> 00:07:27,330
to do with the statement.

84
00:07:27,340 --> 00:07:32,860
He's stuck, he's confused, and he's going to fail the execution once we do that.

85
00:07:33,130 --> 00:07:39,790
So we, first of all, need to create a variable and then to put value to it.

86
00:07:39,790 --> 00:07:42,130
And only then we can use in the math section.

87
00:07:43,420 --> 00:07:51,820
So we never created the X here and we have here name error, name X is not defined also line number

88
00:07:51,820 --> 00:07:52,930
and filename as well.

89
00:07:54,550 --> 00:08:02,220
Index error is caused when reaching out for a sell off collection by index and that index does not exist.

90
00:08:02,650 --> 00:08:06,070
OK, so we have a list here that at least have three.

91
00:08:06,070 --> 00:08:07,570
Index three is the last one.

92
00:08:07,750 --> 00:08:12,040
And here we try out to pull index six, which is.

93
00:08:13,090 --> 00:08:17,920
Does not exist, basically, so we have index our list, index out of range.

94
00:08:21,970 --> 00:08:29,830
All right, so we have indention error, as you already know, Python has indention rules and these

95
00:08:29,830 --> 00:08:36,720
inventions, they basically give us the hierarchy of the code and the flow of code.

96
00:08:36,730 --> 00:08:42,700
And we need to keep you keep implementing according to indention rules.

97
00:08:43,160 --> 00:08:49,420
So in this case, you can see here that equals force equals four does not have an intention, but the

98
00:08:49,420 --> 00:08:52,650
print afterwards has indention, and that's wrong.

99
00:08:52,660 --> 00:08:58,870
This will cause our code to fail and raise the exception in the error least index out of range.

100
00:09:00,760 --> 00:09:09,010
Kierra wants to try to call out a dictionary cell with a wrong or nonexistent key, so we have the key

101
00:09:09,220 --> 00:09:15,700
here, A, B, C, the value one, and then we try to reach out by using the key Z, and that key does

102
00:09:15,700 --> 00:09:16,360
not exist.

103
00:09:16,510 --> 00:09:18,880
So we're going to get an indention error.

104
00:09:19,000 --> 00:09:28,420
Unexpecting indent eight one in line value error will be caused by using a wrong value, a value that

105
00:09:28,420 --> 00:09:30,140
cannot be used in a certain command.

106
00:09:30,400 --> 00:09:33,370
So we're trying to cast the string dog.

107
00:09:33,710 --> 00:09:40,060
Dog is obviously letters and we're trying to to make it to convert it to Cassity to an end.

108
00:09:40,690 --> 00:09:42,040
This cannot be possible.

109
00:09:42,370 --> 00:09:46,630
And we're going to have this exception value for dog.

110
00:09:49,110 --> 00:09:56,100
OK, so these items were the common exceptions that you're going to encounter in your code, basically

111
00:09:56,790 --> 00:10:01,700
you're going to have many more exceptions in general in Python.

112
00:10:01,950 --> 00:10:07,770
And once you encountered the you just Google it and you find the exact explanation why the exception

113
00:10:07,770 --> 00:10:08,350
happened.

114
00:10:08,370 --> 00:10:14,660
And once you know why, you can either fix it or to overcome it in some different techniques.

115
00:10:15,030 --> 00:10:15,510
Thank you.

116
00:10:15,510 --> 00:10:16,920
And I will see you in the next lecture.