0
1
00:00:00,790 --> 00:00:07,720
Now that we've covered the theory behind the Naive Bayes Classifier in detail, it's time to get our hands
1

2
00:00:07,720 --> 00:00:11,430
dirty and write some Python code. In this lesson,
2

3
00:00:11,440 --> 00:00:17,080
we've got a big and important topic coming up, namely how do you get your code to talk to your computer's
3

4
00:00:17,170 --> 00:00:18,650
operating system?
4

5
00:00:18,670 --> 00:00:21,480
How do you read a file?
5

6
00:00:21,500 --> 00:00:25,850
Now a lot of this knowledge is going to be transferable to whatever programming language you're working
6

7
00:00:25,850 --> 00:00:27,900
in and whatever project you're working in.
7

8
00:00:28,040 --> 00:00:32,540
But with Python and machine learning, you're gonna be working with a lot of data and that data is gonna
8

9
00:00:32,540 --> 00:00:33,710
be stored somewhere.
9

10
00:00:34,250 --> 00:00:40,700
Most likely that's going to be stored locally on your computer or it's gonna be stored on a server. For
10

11
00:00:40,700 --> 00:00:45,890
many of our projects, our Python code is going to need to interact with our own computer's operating
11

12
00:00:45,890 --> 00:00:50,700
system and actually be able to read the files from the disk.
12

13
00:00:50,720 --> 00:00:55,580
So while we're on this topic about learning how to read files, we're also going to cover quite a few
13

14
00:00:55,580 --> 00:01:01,530
other topics as well, namely file paths, file locations, file extensions.
14

15
00:01:01,580 --> 00:01:06,650
We're also going to see how our email data is actually structured and we're also going to see how we
15

16
00:01:06,650 --> 00:01:11,120
can extract a message body from a raw email.
16

17
00:01:11,150 --> 00:01:12,810
But first things first.
17

18
00:01:12,950 --> 00:01:18,860
Whenever you're referencing a file in your Python code you're going to need to specify exactly where
18

19
00:01:18,860 --> 00:01:21,820
that file is and what that file is called.
19

20
00:01:21,980 --> 00:01:31,430
And this means you have to specify two things, namely the file path and the file name. In the lesson resources
20

21
00:01:31,550 --> 00:01:35,120
that you've downloaded and added to your projects folder,
21

22
00:01:35,120 --> 00:01:38,260
I included a practice email.
22

23
00:01:38,270 --> 00:01:48,230
So taking a peek inside the spam data folder and then opening "01_Processing", you should see a file called
23

24
00:01:48,320 --> 00:01:52,150
"practice_email.txt".
24

25
00:01:52,280 --> 00:01:56,450
Now, the file name for this file should be pretty obvious because we're looking right at it.
25

26
00:01:56,510 --> 00:02:04,280
It's "practice_email.txt". That "txt" part is called the file extension and this signals
26

27
00:02:04,370 --> 00:02:08,340
what kind of file this is. A txt file
27

28
00:02:08,420 --> 00:02:16,520
is just a boring old text file, but the thing is, these file extensions are key to the computer or you
28

29
00:02:16,520 --> 00:02:20,270
or me understanding what kind of file it is that we're working with.
29

30
00:02:20,360 --> 00:02:24,710
The extension tells us something about a file's format.
30

31
00:02:24,710 --> 00:02:33,980
So for example, Microsoft Word documents have the extension "doc" or "docx" and PDFs have the extension
31

32
00:02:34,310 --> 00:02:41,920
".pdf". Windows executable files on the other hand have the very dangerous extension ".exe".
32

33
00:02:42,260 --> 00:02:50,110
So if you ever receive an email that has an attachment with a ".exe" extension, don't open the attachment.
33

34
00:02:50,120 --> 00:02:55,310
This was always the classic way that people installed viruses on their computers back in the day.
34

35
00:02:55,490 --> 00:03:00,560
I was going through my spam directory recently and one thing I noticed actually was that more and more
35

36
00:03:00,560 --> 00:03:07,400
folks are sending out their malicious code with the ".js" or JavaScript extension instead of 
36

37
00:03:07,430 --> 00:03:08,330
"exe".
37

38
00:03:08,360 --> 00:03:16,760
So yeah, it's always good to pay close attention to these file extensions. Now that we've talked about
38

39
00:03:16,880 --> 00:03:20,070
the file name and the file extension,
39

40
00:03:20,090 --> 00:03:21,860
what about this other thing that I've mentioned?
40

41
00:03:21,860 --> 00:03:29,270
What about the path? The path or the file path is the location of the file.
41

42
00:03:29,270 --> 00:03:33,920
Let me quickly show you how you can actually view the file path on Mac
42

43
00:03:33,920 --> 00:03:37,250
and afterwards I'll show you how to see it on Windows.
43

44
00:03:37,250 --> 00:03:42,550
If you're using a Mac, then you can open Finder and you can go to this "practice_
44

45
00:03:42,560 --> 00:03:50,300
email.txt" file in Finder and then you can go to "File" > "Get Info" or Command+I
45

46
00:03:50,360 --> 00:03:56,820
and what you can see right here is the location of this file.
46

47
00:03:56,890 --> 00:04:02,590
It's on my hard drive, under my username, inside my projects folder,
47

48
00:04:02,740 --> 00:04:06,340
then SpamData and then 01_Processing.
48

49
00:04:06,340 --> 00:04:12,160
This here is the location of the "practice_email.txt" file.
49

50
00:04:12,220 --> 00:04:19,810
This right here is my file path. If you're running Windows on the other hand, you can always see the file
50

51
00:04:19,810 --> 00:04:24,490
path and the location in this address bar right up here.
51

52
00:04:24,490 --> 00:04:27,430
So right now this is the project's folder,
52

53
00:04:27,430 --> 00:04:35,700
double clicking on SpamData will open my folder and you can see now that the location here has updated.
53

54
00:04:35,770 --> 00:04:44,800
If I open "Processing" then I can clearly see the full file path to this practice email right here in
54

55
00:04:44,800 --> 00:04:53,800
my address bar. If I click inside the address bar, then we can see the names of the folders and the sub
55

56
00:04:53,800 --> 00:04:57,910
folders separated by a backslash.
56

57
00:04:57,910 --> 00:05:04,630
In other words, my Processing folder is inside SpamData which is inside my projects folder which is
57

58
00:05:04,630 --> 00:05:10,780
inside my username folder under Users and then on my C drive.
58

59
00:05:11,140 --> 00:05:17,850
This long piece of text that we're looking at right here is the full path. And this brings me to the
59

60
00:05:17,850 --> 00:05:21,510
two different kind of paths that you'll be encountering.
60

61
00:05:21,570 --> 00:05:30,190
The first one is actually called an absolute path. Think of the absolute path as the long form.
61

62
00:05:30,250 --> 00:05:34,090
This is the full path to the file or folder. On Windows,
62

63
00:05:34,090 --> 00:05:40,330
you often see the absolute path starting with C and then going to your particular user profile and then
63

64
00:05:40,330 --> 00:05:44,050
down to a particular folder. On Mac,
64

65
00:05:44,050 --> 00:05:49,070
the absolute path to the practice email would look something more like this.
65

66
00:05:49,430 --> 00:05:49,880
All right.
66

67
00:05:49,930 --> 00:05:58,000
I think that's easy enough. But, while the absolute path is the long form, there is also a shorthand. You
67

68
00:05:58,000 --> 00:06:02,050
see, you don't always have to work with an absolute path.
68

69
00:06:02,050 --> 00:06:10,860
Instead, you can work with what's called a relative path. A relative path uses your current location as
69

70
00:06:10,860 --> 00:06:16,680
the starting location and then points to a file or folder from there.
70

71
00:06:16,710 --> 00:06:24,780
So suppose I'm in my MLProjects folder in Finder, then the relative path to the practice email would
71

72
00:06:24,780 --> 00:06:28,850
be SpamData, 01_Processing
72

73
00:06:29,100 --> 00:06:30,510
and there it is.
73

74
00:06:30,600 --> 00:06:38,110
There is my "practice_email.txt" file. As such, the relative path from my MLProjects
74

75
00:06:38,110 --> 00:06:44,620
folder to my practice_email.txt file would look something like this.
75

76
00:06:44,800 --> 00:06:50,700
What you're looking at here is actually the formatting for windows. On a Mac,
76

77
00:06:50,710 --> 00:06:55,720
you'd have a relative path that would look more like this. Notice,
77

78
00:06:55,780 --> 00:07:02,620
the only difference are the slashes. Mac uses the forward slash and Windows uses the backslash in front
78

79
00:07:02,620 --> 00:07:04,900
of the file and folder names.
79

80
00:07:04,900 --> 00:07:08,980
Now this might be a small thing to point out, but the direction of the slashes actually matters when
80

81
00:07:08,980 --> 00:07:10,820
you're writing your Python code.
81

82
00:07:10,870 --> 00:07:16,930
So even though in Windows you see backslash is used in the path on the address bar,
82

83
00:07:16,990 --> 00:07:24,040
it's actually a little problematic to try and just copy paste what's in here and the reason is is that
83

84
00:07:24,130 --> 00:07:30,940
in Python you actually want to use a forward slash, because the backslash has a special purpose in the
84

85
00:07:30,940 --> 00:07:33,150
Python programming language.
85

86
00:07:33,220 --> 00:07:39,370
Let's fire up a new Python notebook and I'll show you exactly what I mean and why we want to use forward
86

87
00:07:39,370 --> 00:07:46,130
slashes. In Jupyter navigate to your MLProjects folder and then click "New" >
87

88
00:07:46,370 --> 00:07:59,540
"Python 3" notebook. Let's rename this notebook to "06 Bayes Classifier" and click "Rename". Say we print a line
88

89
00:07:59,750 --> 00:08:02,970
'What is up?' and hit Shift+Enter.
89

90
00:08:02,990 --> 00:08:04,790
Then we see this text printed below.
90

91
00:08:05,630 --> 00:08:08,930
But what if we wanted to write 'What's up?'.
91

92
00:08:08,930 --> 00:08:13,130
So if I wanted to write "What's up?" with an apostrophe,
92

93
00:08:13,130 --> 00:08:22,940
you can see that I now have three single quotes in this string and that means that my string starts
93

94
00:08:22,940 --> 00:08:30,920
here, ends here and this part onwards here is considered Python code and then it starts another string
94

95
00:08:30,920 --> 00:08:31,800
here.
95

96
00:08:31,850 --> 00:08:39,030
In other words, Python needs to know that it should ignore this single quote and for that we use the
96

97
00:08:39,030 --> 00:08:44,480
backslash. The backslash escapes the character that follows it.
97

98
00:08:44,580 --> 00:08:50,130
So by using the backslash, this single quote here is treated as part of the string
98

99
00:08:50,280 --> 00:08:55,980
and if I hit Shift+Enter, I can get that apostrophe to show up in my output.
99

100
00:08:56,190 --> 00:09:03,960
And that's also why when you're providing a path as a string, you want to make sure use forward slashes
100

101
00:09:04,230 --> 00:09:11,690
instead of backslash is that you get from copy and pasting from the Windows address bar. Okay,
101

102
00:09:11,710 --> 00:09:20,420
so so much for the theory behind relative paths, file names, file extensions and absolute paths. In the next
102

103
00:09:20,420 --> 00:09:21,050
lesson,
103

104
00:09:21,170 --> 00:09:25,760
I'll show you how to read that practice email into Jupyter notebook.
104

105
00:09:25,760 --> 00:09:29,630
I'm gonna go ahead and get some coffee, but I hope I'll see you on the next lesson.