1
00:00:00,000 --> 00:00:02,790
Good, we were able to transform our

2
00:00:02,790 --> 00:00:05,280
script, which was built using functions.

3
00:00:05,820 --> 00:00:09,120
And we created a class and put those

4
00:00:09,120 --> 00:00:11,070
functions inside that class. So they are

5
00:00:11,070 --> 00:00:14,520
now called methods. And while this is a

6
00:00:14,520 --> 00:00:17,520
use of a class, it's still not the

7
00:00:17,520 --> 00:00:19,920
best use of Object Oriented Programming

8
00:00:19,920 --> 00:00:23,340
paradigm. Because we have a database

9
00:00:23,340 --> 00:00:25,650
here, a database object that is being

10
00:00:25,680 --> 00:00:29,010
created, but we are not treating it as a

11
00:00:29,010 --> 00:00:33,780
solid object. So we are opening it and

12
00:00:33,780 --> 00:00:37,590
closing it in every method. So what I'm

13
00:00:37,590 --> 00:00:41,820
thinking is, we create a connection when

14
00:00:41,820 --> 00:00:44,670
we call the class. So when this function

15
00:00:44,670 --> 00:00:47,310
is executed, we create a connection

16
00:00:47,310 --> 00:00:49,110
there, and we keep that connection

17
00:00:49,140 --> 00:00:53,850
opened. So I don't include this close

18
00:00:54,030 --> 00:00:56,790
method there. But I'll leave the commit

19
00:00:56,790 --> 00:01:01,020
method in case there is no table and a

20
00:01:01,020 --> 00:01:03,060
table will be created, and the changes

21
00:01:03,060 --> 00:01:04,980
will be committed to the open

22
00:01:04,980 --> 00:01:07,590
connection. Now, because we have a

23
00:01:07,590 --> 00:01:09,960
connection open there, we don't need to

24
00:01:09,960 --> 00:01:14,370
establish a new one in each method. We

25
00:01:14,370 --> 00:01:16,500
don't even need to create a cursor

26
00:01:16,500 --> 00:01:18,720
object, because the cursor object is

27
00:01:18,720 --> 00:01:21,420
being created in here. So we get rid of

28
00:01:21,450 --> 00:01:26,520
those two lines in every single method.

29
00:01:28,350 --> 00:01:31,410
So in view, we have a cursor object when

30
00:01:31,410 --> 00:01:34,380
we go here, and then we execute this

31
00:01:34,800 --> 00:01:36,990
statement to that cursor object. So that

32
00:01:36,990 --> 00:01:42,450
is good. There we go down here, these

33
00:01:42,450 --> 00:01:46,188
two also and for the delete method

34
00:01:46,189 --> 00:01:50,278
[Author typing]

35
00:01:50,280 --> 00:01:55,290
and update as well. Great. Now let's see how

36
00:01:55,290 --> 00:01:58,050
this goes. Let me make this closer.

37
00:01:58,052 --> 00:02:03,628
[Author typing]

38
00:02:03,630 --> 00:02:05,850
So we call the frontend script where we

39
00:02:05,850 --> 00:02:08,340
are creating an instance of our object.

40
00:02:09,090 --> 00:02:12,476
So far, so good View all.

41
00:02:12,477 --> 00:02:14,829
[No audio]

42
00:02:14,831 --> 00:02:21,054
And it says that name cur is not defined in line 17.

43
00:02:23,210 --> 00:02:28,680
So we executed the view method. And

44
00:02:28,680 --> 00:02:30,990
what the view method does is it tries to

45
00:02:30,990 --> 00:02:34,200
find a variable or declared variable

46
00:02:34,230 --> 00:02:36,930
inside the function. So the cur

47
00:02:36,930 --> 00:02:38,730
variable it doesn't find, so then it

48
00:02:38,730 --> 00:02:41,640
looks if there is a variable outside the

49
00:02:41,640 --> 00:02:44,160
function, and it doesn't find it.

50
00:02:44,160 --> 00:02:46,140
Actually, there is a variable that has

51
00:02:46,140 --> 00:02:49,380
been declared in this init function, but

52
00:02:49,410 --> 00:02:52,650
this is a local variable. So this has

53
00:02:52,650 --> 00:02:56,671
value only inside this function. So you cannot

54
00:02:56,672 --> 00:03:01,863
access this outside of the init function. But if we

55
00:03:01,864 --> 00:03:04,797
[Author typing]

56
00:03:04,798 --> 00:03:09,990
refer to the self argument, which is the database object

57
00:03:11,640 --> 00:03:16,230
and see what we get and we close this, save.

58
00:03:16,231 --> 00:03:20,368
[No audio]

59
00:03:20,370 --> 00:03:23,280
That works and View all. Now we get

60
00:03:23,310 --> 00:03:25,770
another type of error. And it says

61
00:03:25,770 --> 00:03:30,090
attribute error. So let me close this. So

62
00:03:30,090 --> 00:03:32,352
look carefully here, and it says

63
00:03:32,399 --> 00:03:35,460
a database object has no attribute cur.

64
00:03:36,090 --> 00:03:39,210
And that's in line 17. So this one

65
00:03:39,210 --> 00:03:42,570
here, the database object, this one is

66
00:03:42,570 --> 00:03:46,320
this one here. So self has been replaced

67
00:03:46,320 --> 00:03:50,250
by database, which is the object created

68
00:03:50,250 --> 00:03:54,600
by this class. This is an attribute of

69
00:03:54,630 --> 00:03:57,930
this object. To fix that, we need to

70
00:03:57,930 --> 00:04:01,710
create an attribute there. So we say

71
00:04:01,710 --> 00:04:05,730
self.cursor .cur equals to

72
00:04:05,730 --> 00:04:08,520
connection.cursor. So the cursor

73
00:04:08,520 --> 00:04:11,820
method or the connection object of the

74
00:04:11,820 --> 00:04:17,557
sqlite3 library. Now if we try again, the code

75
00:04:17,558 --> 00:04:20,149
[No audio]

76
00:04:20,151 --> 00:04:23,703
it says name cur is not defined in line 8.

77
00:04:25,432 --> 00:04:29,037
So now that's we created an attributes this is

78
00:04:29,054 --> 00:04:31,680
trying to find the variable cur. So the

79
00:04:31,680 --> 00:04:34,170
local variable cur, which is not in

80
00:04:34,170 --> 00:04:36,360
this function, because now this is an

81
00:04:36,360 --> 00:04:40,080
attribute of the class. So that means we

82
00:04:40,080 --> 00:04:43,080
need to refer to self here as well. So

83
00:04:43,080 --> 00:04:46,140
to the object and then cur.execute and

84
00:04:46,140 --> 00:04:50,910
so on. So, if we try this now, View all we

85
00:04:50,910 --> 00:04:52,920
get another line code is not defined in

86
00:04:52,920 --> 00:04:57,300
line 18. So here, that means you need to

87
00:04:57,300 --> 00:05:01,770
do the same and we don't have any

88
00:05:01,800 --> 00:05:04,410
cur variable anymore, we have the

89
00:05:04,410 --> 00:05:07,260
cur attribute. So now if I run this,

90
00:05:07,260 --> 00:05:09,750
again, I'll get probably an error about

91
00:05:09,750 --> 00:05:12,990
the connection this time, the conn

92
00:05:13,410 --> 00:05:16,890
variable, View all here, conn is not

93
00:05:16,890 --> 00:05:21,150
defined in line 19. So again, this view

94
00:05:21,150 --> 00:05:23,190
function is trying to find the variable

95
00:05:23,190 --> 00:05:27,090
conn connection. So self commit there,

96
00:05:27,660 --> 00:05:30,416
and here as well. So you declare the attribute

97
00:05:30,418 --> 00:05:34,852
there, and it can be the changes down here.

98
00:05:34,853 --> 00:05:38,283
[No audio]

99
00:05:38,285 --> 00:05:42,480
self.connection.close. So

100
00:05:42,480 --> 00:05:44,910
that looks good now. rows equals to

101
00:05:44,910 --> 00:05:47,370
this rows is just a local variable

102
00:05:47,580 --> 00:05:49,830
that is created here and then we return

103
00:05:49,860 --> 00:05:53,682
the fetched rows from this expression.

104
00:05:54,647 --> 00:05:57,269
So this method returns this when it is being

105
00:05:57,270 --> 00:06:03,694
called in this script, just here. Good.

106
00:06:03,695 --> 00:06:05,820
[No audio]

107
00:06:05,822 --> 00:06:09,757
And let me try what do we have at this point?

108
00:06:09,758 --> 00:06:12,786
[No audio]

109
00:06:12,788 --> 00:06:18,360
Line 7 name conn is not defined. Yeah, we

110
00:06:18,360 --> 00:06:22,740
need to do the same for these two. And

111
00:06:22,740 --> 00:06:25,710
everything looks good now. So let's try

112
00:06:25,740 --> 00:06:28,440
again. Yeah, View all and now we get the

113
00:06:28,440 --> 00:06:32,100
data there. But when I press it for a

114
00:06:32,100 --> 00:06:34,920
second time, we get yet another error.

115
00:06:35,940 --> 00:06:38,610
And so it says cannot operate on a close

116
00:06:38,640 --> 00:06:43,290
database. So why is that? Now well, I press

117
00:06:43,290 --> 00:06:46,050
the View button once, and this method was

118
00:06:46,050 --> 00:06:50,310
executed, so the cursor object was able

119
00:06:50,310 --> 00:06:54,510
to fetch these data. And then we close

120
00:06:54,510 --> 00:06:57,180
the connection or return the rows. So we

121
00:06:57,180 --> 00:07:00,780
were able to get those three rows there.

122
00:07:01,470 --> 00:07:03,210
But then when I press the View button

123
00:07:03,210 --> 00:07:06,660
for a second time, the view method faces

124
00:07:06,840 --> 00:07:09,750
close connection. So that's why you get

125
00:07:09,750 --> 00:07:11,910
this cannot operate on a close database

126
00:07:11,940 --> 00:07:15,934
error. So and see what we get.

127
00:07:17,674 --> 00:07:22,710
So View all it's working well. Yep. That means

128
00:07:22,710 --> 00:07:26,670
we can go ahead and modify the other

129
00:07:26,670 --> 00:07:30,970
methods. So self.cursor and

130
00:07:31,259 --> 00:07:35,730
self.connection and remove this close. Let's

131
00:07:35,730 --> 00:07:37,470
think about closing the connection later

132
00:07:37,470 --> 00:07:41,280
on. So don't focus on that now. Just try

133
00:07:41,280 --> 00:07:44,970
to make this method to work self here,

134
00:07:45,224 --> 00:07:51,014
self there, and there. Again, for the

135
00:07:51,060 --> 00:07:56,610
delete methods and remove the connection.close.

136
00:07:56,612 --> 00:08:02,368
[Author typing]

137
00:08:02,370 --> 00:08:04,920
And everything should work fine at this

138
00:08:04,920 --> 00:08:08,760
point. So let's see View all, well this is

139
00:08:08,760 --> 00:08:11,250
working, let's search for something to

140
00:08:11,250 --> 00:08:17,970
see and Search entry. We got one cursor there.

141
00:08:19,491 --> 00:08:25,281
So cur is now defined in search. Yeah. Sorry.

142
00:08:25,282 --> 00:08:27,400
[Author typing]

143
00:08:27,402 --> 00:08:29,652
Again, View all, View all,

144
00:08:29,653 --> 00:08:32,250
[Author typing]

145
00:08:32,250 --> 00:08:36,870
see Search entry. And yet another name

146
00:08:36,870 --> 00:08:39,750
error, name rows is not defined.

147
00:08:41,610 --> 00:08:46,680
So by mistake, I converted this local

148
00:08:46,680 --> 00:08:50,490
variable to an attributes. So rows here, rows

149
00:08:50,490 --> 00:08:56,340
there. Okay, one more time. View all, View all.

150
00:08:56,341 --> 00:08:58,978
[Author typing]

151
00:08:58,980 --> 00:09:00,585
And now seems to be working.

152
00:09:02,491 --> 00:09:04,050
So let's add some data.

153
00:09:04,051 --> 00:09:09,833
[Author typing]

154
00:09:09,835 --> 00:09:12,720
Add entry there and cannot operate on a

155
00:09:12,720 --> 00:09:19,440
close database. Why? Because all in

156
00:09:19,440 --> 00:09:21,780
the search method, we have a close

157
00:09:21,810 --> 00:09:24,851
database. So we close database there. And

158
00:09:24,852 --> 00:09:28,879
I overlooked that so we don't have any more.

159
00:09:28,880 --> 00:09:32,154
[No audio]

160
00:09:32,156 --> 00:09:35,402
close methods that are knew. So let's

161
00:09:35,403 --> 00:09:39,540
try one more time there. Sorry about that.

162
00:09:39,541 --> 00:09:46,168
[Author typing]

163
00:09:46,170 --> 00:09:48,649
Add entry and now it seems to be working fine.

164
00:09:48,650 --> 00:09:51,026
[Author typing]

165
00:09:51,028 --> 00:09:54,990
Great. So everything looks good.

166
00:09:55,380 --> 00:09:58,200
Except of we don't have the close

167
00:09:58,200 --> 00:10:00,840
method anymore because we can't keep

168
00:10:00,840 --> 00:10:03,300
that method, either method of our

169
00:10:03,300 --> 00:10:05,820
class. Because you saw that when we have

170
00:10:05,820 --> 00:10:08,490
that method there, and we end up with this

171
00:10:08,520 --> 00:10:11,910
error. Or you can leave the code without

172
00:10:12,780 --> 00:10:16,350
close method, but you'd done up with

173
00:10:16,350 --> 00:10:18,870
some problems later, because if you have

174
00:10:19,080 --> 00:10:20,550
some methods that have not been

175
00:10:20,550 --> 00:10:23,010
committed, then when another

176
00:10:23,010 --> 00:10:24,870
program connects to your database, and

177
00:10:24,870 --> 00:10:28,260
then these data will be committed with

178
00:10:28,260 --> 00:10:30,570
the next operation, so it messes some

179
00:10:30,570 --> 00:10:34,110
things up sometimes. So, as a rule, you

180
00:10:34,110 --> 00:10:37,140
should close the connection. And to do

181
00:10:37,140 --> 00:10:41,100
that very similar spatial methods that

182
00:10:41,100 --> 00:10:44,400
you can add to your class like this one

183
00:10:44,400 --> 00:10:47,730
here, but this other one is for

184
00:10:48,210 --> 00:10:52,140
destructing your object that is called

185
00:10:52,380 --> 00:10:57,090
del. So for delete, and this also gets

186
00:10:57,900 --> 00:11:00,630
the object thesis as a parameter. So

187
00:11:00,660 --> 00:11:05,070
this method is applied, is executed when

188
00:11:05,070 --> 00:11:08,040
you call them an instance of the class

189
00:11:08,040 --> 00:11:10,650
like we are doing in frontend script,

190
00:11:11,130 --> 00:11:15,090
just here. While this one here, this is

191
00:11:15,090 --> 00:11:18,690
executed when this instance is deleted

192
00:11:18,720 --> 00:11:21,750
from the script, which happens to be

193
00:11:21,750 --> 00:11:24,960
when the script is executed. So before

194
00:11:24,960 --> 00:11:29,390
the script exits this method will be executed. And

195
00:11:29,391 --> 00:11:33,808
what we want to do here is self.connection.close.

196
00:11:33,809 --> 00:11:35,872
[No audio]

197
00:11:35,874 --> 00:11:38,797
So that should do the trick. Now if you

198
00:11:38,798 --> 00:11:41,269
try out this, we should get the same

199
00:11:41,270 --> 00:11:43,743
[Author typing]

200
00:11:43,745 --> 00:11:47,500
results. So I added this by mistake. But

201
00:11:47,501 --> 00:11:51,570
anyway, so let's see, you can search for that and

202
00:11:51,570 --> 00:11:55,620
get the rows with that particular value.

203
00:11:57,420 --> 00:12:00,120
So this is my solution. And that's

204
00:12:00,120 --> 00:12:02,610
not standard way to write a script. So

205
00:12:02,850 --> 00:12:04,980
there may be other alternatives to

206
00:12:04,980 --> 00:12:08,040
solve this problem. So to build this

207
00:12:08,070 --> 00:12:11,040
application, so you may also choose to

208
00:12:11,670 --> 00:12:15,660
add the method there or here in the

209
00:12:16,110 --> 00:12:18,030
Graphical User Interface. So you could

210
00:12:18,030 --> 00:12:19,920
do something like you add a button like

211
00:12:19,950 --> 00:12:22,950
commit button, and then, here you add

212
00:12:22,950 --> 00:12:26,700
another method called commit. And then

213
00:12:26,700 --> 00:12:30,090
you remove probably all this commit

214
00:12:30,090 --> 00:12:32,850
methods from these methods from the

215
00:12:32,850 --> 00:12:36,180
methods of your SQLite operations,

216
00:12:36,210 --> 00:12:38,190
and then you put that method, so one

217
00:12:38,190 --> 00:12:42,720
method commit inside that commit method

218
00:12:42,750 --> 00:12:45,990
of your class. So when the user presses

219
00:12:45,990 --> 00:12:47,490
commit, and then you can make the changes

220
00:12:47,490 --> 00:12:49,320
to the database. So that would be

221
00:12:49,320 --> 00:12:52,380
another solution. But this is what we

222
00:12:52,380 --> 00:12:56,640
came up with in this particular case. So

223
00:12:56,640 --> 00:12:58,620
I hope you understand a few things. Now,

224
00:12:59,040 --> 00:13:01,530
Alice is rarely used. So normally, you

225
00:13:01,590 --> 00:13:03,630
only have to use init, and then the

226
00:13:03,630 --> 00:13:06,210
other methods, but this is appropriate

227
00:13:06,210 --> 00:13:09,090
when you want to apply something just

228
00:13:09,090 --> 00:13:11,700
before exiting the program. So that's

229
00:13:11,700 --> 00:13:14,640
great. And in the next lecture, how we will

230
00:13:14,670 --> 00:13:17,700
write another class. So we will think

231
00:13:17,700 --> 00:13:20,100
about how to model a problem, which is

232
00:13:20,100 --> 00:13:23,670
about creating some sort of bank account

233
00:13:23,700 --> 00:13:26,430
object where we store a balance of

234
00:13:26,430 --> 00:13:30,060
money. And then we withdraw and deposit

235
00:13:30,060 --> 00:13:32,940
the money into this balance. Now as an

236
00:13:32,940 --> 00:13:37,170
exercise, you can convert this script,

237
00:13:37,650 --> 00:13:40,800
solid tkinter part of the program of the

238
00:13:40,800 --> 00:13:44,220
frontend, into an Object Oriented

239
00:13:44,280 --> 00:13:48,180
form. So you put these inside a class

240
00:13:48,180 --> 00:13:50,760
and try to come up with a good

241
00:13:50,760 --> 00:13:53,430
solution. I'll also provide you a

242
00:13:53,430 --> 00:13:56,130
solution to this. But before that I would

243
00:13:56,130 --> 00:13:58,080
like to try out yourself. So you

244
00:13:58,080 --> 00:14:00,090
practice Object Oriented Programming a

245
00:14:00,090 --> 00:14:03,120
little bit. Yeah, that's good. We

246
00:14:03,120 --> 00:14:04,950
that's, I'll see you in the next lecture.

247
00:14:04,951 --> 00:14:06,995
[No audio]