1
00:00:00,330 --> 00:00:08,130
So now the world sees this particular fight scene drive and let us see which by the name.

2
00:00:10,960 --> 00:00:13,690
Substitution cipher Benmore.

3
00:00:18,950 --> 00:00:20,510
Not Levi.

4
00:00:21,620 --> 00:00:28,340
In the same folder, you'll see it and now let us try and execute them or you find it is double is equal

5
00:00:28,340 --> 00:00:28,880
to here.

6
00:00:29,630 --> 00:00:36,290
So again, let us save it and try to run this in an error or this implicit fine.

7
00:00:36,320 --> 00:00:37,430
Let us check this.

8
00:00:37,530 --> 00:00:38,490
What is the error?

9
00:00:38,900 --> 00:00:43,990
Let's see if the key that we have taken is proper and it should not be repeated.

10
00:00:44,030 --> 00:00:46,640
So let us just validate that key first.

11
00:00:47,090 --> 00:00:53,210
So here, the key that we have taken is L.F. w o a ViiV.

12
00:00:53,720 --> 00:01:04,550
Then you have you I s we he and then you have a, b, b, d, c are.

13
00:01:05,300 --> 00:01:09,910
Then you have g, d, q he said.

14
00:01:10,460 --> 00:01:14,530
So as far as we see that is more characters repeating over here.

15
00:01:15,140 --> 00:01:17,930
So let us check what we have passed.

16
00:01:18,320 --> 00:01:19,400
He is what it is.

17
00:01:19,670 --> 00:01:29,060
We have the Michy orbit and when in this particular function that this is what it is, we are passing

18
00:01:29,060 --> 00:01:32,480
the list asdf that's equal to the list.

19
00:01:32,750 --> 00:01:34,310
Start here and let us.

20
00:01:34,310 --> 00:01:38,150
This list is equal to the letter this year that we have created.

21
00:01:38,150 --> 00:01:44,960
And the list as you are sorting it, and this is also something, then we are returning the test which

22
00:01:44,960 --> 00:01:46,880
is equal to that of this test.

23
00:01:47,160 --> 00:01:53,600
OK, so if this is coming us valuable here, then we are giving a system.

24
00:01:53,600 --> 00:01:55,180
Not in that case.

25
00:01:55,760 --> 00:02:02,540
Now what are we supposed to do is we have missed here, if not valid, then I'm going to give an ETA

26
00:02:02,900 --> 00:02:06,440
if it is valid, because this would if it is regarding this, are valid.

27
00:02:07,070 --> 00:02:11,240
So if it is a valid ticket, then we are moving for encryption.

28
00:02:11,420 --> 00:02:15,590
So now if we try to execute this, we get the encrypted message.

29
00:02:16,460 --> 00:02:23,930
Now we would copy down this message here and paste it or substitute that over here.

30
00:02:23,960 --> 00:02:29,200
So let's add it below my message of.

31
00:02:30,490 --> 00:02:41,530
They start here and we will just come into this for the time, let's save this and let us execute one

32
00:02:41,530 --> 00:02:42,600
more mistake we made.

33
00:02:43,090 --> 00:02:46,130
This is not and this is different.

34
00:02:46,570 --> 00:02:49,030
Save it and run it.

35
00:02:49,510 --> 00:02:51,850
So this is all we are decrypting.

36
00:02:51,850 --> 00:02:54,590
It got the same message that we from within.

37
00:02:54,850 --> 00:02:55,220
Right.

38
00:02:55,600 --> 00:02:59,510
So now let us understand the food that we have written here.

39
00:02:59,800 --> 00:03:06,940
First thing is we are importing the paperclip system and random modules and the letters are variable

40
00:03:06,940 --> 00:03:13,210
is set to a string of all the uppercase letters, which is this implicit for a simple substitution cipher

41
00:03:13,210 --> 00:03:13,660
program.

42
00:03:14,200 --> 00:03:20,590
Then we have the main function, which is similar to the main function of cipher program in which we

43
00:03:20,590 --> 00:03:27,880
basically call when the program is run first and it contains variable that stores the messages and immodesty

44
00:03:27,880 --> 00:03:29,410
are used for the program.

45
00:03:29,740 --> 00:03:36,310
Now the keys for a simple substitution cipher are easy to get wrong because it's fairly long and need

46
00:03:36,310 --> 00:03:38,680
to have every letter in the alphabet.

47
00:03:38,980 --> 00:03:45,850
So, for example, it is easy to enter a key that is missing, a key that has the same letter twice,

48
00:03:45,850 --> 00:03:53,080
for example, and then check that if your key is valid function, make sure the keys usable by the encryption

49
00:03:53,290 --> 00:03:55,900
decryption functions so the function exists.

50
00:03:55,900 --> 00:03:58,930
A program with an error message of the key is not valid.

51
00:03:59,470 --> 00:04:06,360
Now in this case, if this particular statement returns false, then the murkiest is contains an invalid

52
00:04:06,610 --> 00:04:12,610
and the program is terminated all over Europe and we are checking whether the mind is still variable,

53
00:04:12,610 --> 00:04:18,640
is said to encrypt or decrypt, and we accordingly, given particular methods, will adhere to the total

54
00:04:18,640 --> 00:04:24,160
value of this particular method would be a string which is encrypted or decrypted message that is stored

55
00:04:24,160 --> 00:04:26,710
in your translated Istria variable.

56
00:04:27,100 --> 00:04:35,500
Now after that, we are copying the value over here, using our copy method on the label so the encrypted

57
00:04:35,500 --> 00:04:39,510
or the decrypted message is printed to the screen and also copied to the clip.

58
00:04:40,420 --> 00:04:47,080
Now after that now next, we will look at how the key is whether this function uses this sort of method

59
00:04:47,080 --> 00:04:49,180
to test whether the key is valid.

60
00:04:49,570 --> 00:04:53,440
So, first of all, we will see understand what is this awfullest material.

61
00:04:53,830 --> 00:04:59,820
Now, the list have a sort of a code that rearranges the list items into numerical order.

62
00:05:00,160 --> 00:05:06,400
And this ability to sort items in the list comes in handy when you have to check whether Doulis contains

63
00:05:06,400 --> 00:05:09,970
the same items, but don't list them in the same order.

64
00:05:10,360 --> 00:05:16,180
So in this particular program, a simple substitution key string value is valid only four times each

65
00:05:16,180 --> 00:05:20,320
time it goes in the symbols set with no duplicate or missing letters.

66
00:05:20,650 --> 00:05:25,600
We can check whether the string value is a valid key by sorting it and checking whether it's equal to

67
00:05:25,600 --> 00:05:27,150
the sorted list or letters.

68
00:05:27,610 --> 00:05:31,410
But we can only list and not strings.

69
00:05:31,690 --> 00:05:36,410
OK, we'll open list of origin of the string values by passing them to the list method.

70
00:05:36,880 --> 00:05:42,250
Then after sorting this list, we can compare the two to see whether or not they are equal.

71
00:05:42,430 --> 00:05:47,380
Now, although later this year is already in the alphabetical order, we will sort it because we will

72
00:05:47,380 --> 00:05:50,160
expand it to contain other characters later.

73
00:05:50,680 --> 00:05:57,280
So hence we are saying string key is passed on to the list method here and the list value written is

74
00:05:57,280 --> 00:05:59,170
stored in the variable named list.

75
00:06:00,490 --> 00:06:07,180
Then the letters constant that we have created this past on again to the list method in the next line,

76
00:06:07,420 --> 00:06:10,670
which is on the list in again all sorted order.

77
00:06:10,690 --> 00:06:17,080
That is again in ABCDE that now after this we are doing here the list in the list.

78
00:06:17,080 --> 00:06:23,770
SDR and the letters list are then sorted in the alphabetical order by calling the sort list method on

79
00:06:23,770 --> 00:06:23,990
them.

80
00:06:24,370 --> 00:06:30,310
Now note that similar to the appendix method, short list also modifies the list in the place and doesn't

81
00:06:30,310 --> 00:06:31,400
have a written value.

82
00:06:31,840 --> 00:06:39,160
So when the list and the letter list SDR values should be the same because he lists SDR will simply

83
00:06:39,160 --> 00:06:42,130
be correct later this year with an order scramble.

84
00:06:42,610 --> 00:06:50,710
So when we check whether the values of Aschiana letters this year are equal, the values are then after

85
00:06:50,710 --> 00:06:55,450
checking it, they are basically written values, then passed on to the matter there.

86
00:06:55,840 --> 00:07:02,740
So over here, in case this returns true if they are equal and have no duplicates, but if your list

87
00:07:02,740 --> 00:07:04,930
is there and that does, it still doesn't match.

88
00:07:04,940 --> 00:07:10,890
The key is invalid and it is written for what's now coming to the wrapper function.

89
00:07:11,110 --> 00:07:15,310
The encryption or the decryption code in the program are almost identical.

90
00:07:15,310 --> 00:07:20,320
If you can see here when you have two similar pieces of code, it's best to put them into a function

91
00:07:20,320 --> 00:07:23,070
and call it twice rather than enter the court.

92
00:07:23,650 --> 00:07:29,060
So not only does this save your time, but also more importantly, it avoids introducing books like

93
00:07:29,060 --> 00:07:29,590
Copying and.

94
00:07:30,740 --> 00:07:38,420
So it's also advantageous because that is very small every quarter and you have to only fix one book

95
00:07:38,420 --> 00:07:41,510
at a time instead of looking at for multiple places.

96
00:07:41,810 --> 00:07:47,510
So this rappel function helps you avoid having to enter duplicate code by wrapping the code of another

97
00:07:47,510 --> 00:07:49,540
function and returning the value.

98
00:07:49,550 --> 00:07:56,120
The wrapped function with often the wrapper function makes a slight change to the arguments of the return

99
00:07:56,120 --> 00:07:57,940
values of the wrapper function.

100
00:07:58,160 --> 00:08:02,750
Otherwise, there would be no need for wrapping because you could just call the function directly.