WEBVTT 1 00:00:00.930 --> 00:00:02.460 Hi guys, and welcome back. 2 00:00:02.460 --> 00:00:04.960 In this video, we're going to start using Python lists 3 00:00:04.960 --> 00:00:07.930 as a database table instead of SQL Lite. 4 00:00:07.930 --> 00:00:10.470 We're going to do this first because it's simpler, 5 00:00:10.470 --> 00:00:12.460 then when we want to use SQL Lite, 6 00:00:12.460 --> 00:00:16.140 the change over will be very straightforward. 7 00:00:16.140 --> 00:00:17.050 When you think about it, 8 00:00:17.050 --> 00:00:19.640 lists and database tables are very similar. 9 00:00:19.640 --> 00:00:23.030 They are both used to store individual items. 10 00:00:23.030 --> 00:00:26.150 Inside a database table, we store rows of data. 11 00:00:26.150 --> 00:00:28.540 And each row can have multiple pieces of data, 12 00:00:28.540 --> 00:00:30.210 one per column. 13 00:00:30.210 --> 00:00:32.760 Inside the list, we can store anything we like, 14 00:00:32.760 --> 00:00:34.810 including dictionaries, 15 00:00:34.810 --> 00:00:39.110 each dictionary can contain multiple pieces of data as well. 16 00:00:39.110 --> 00:00:42.220 So here, I'm going to show you sort of a sample dictionary 17 00:00:42.220 --> 00:00:46.630 that we might store in our list. 18 00:00:46.630 --> 00:00:48.360 So here we've got our entries list, 19 00:00:48.360 --> 00:00:50.720 this is what we're going to be storing in our application. 20 00:00:50.720 --> 00:00:52.350 And you can see that it's a list, 21 00:00:52.350 --> 00:00:55.530 and inside it we've got four dictionaries. 22 00:00:55.530 --> 00:00:58.550 You can imagine that these things are things a user created, 23 00:00:58.550 --> 00:01:01.180 so we've got the content key 24 00:01:01.180 --> 00:01:03.950 that contains what the user learned on that day, 25 00:01:03.950 --> 00:01:07.450 and the date key that contains when they learned it. 26 00:01:07.450 --> 00:01:09.900 Initially, our entries list is going to be empty. 27 00:01:09.900 --> 00:01:11.860 And we will be creating a dictionary 28 00:01:11.860 --> 00:01:14.000 every time the user adds a new entry, 29 00:01:14.000 --> 00:01:16.970 and putting that dictionary into the list. 30 00:01:16.970 --> 00:01:18.290 So this is just an example. 31 00:01:18.290 --> 00:01:21.270 But let's go ahead and write this code out. 32 00:01:21.270 --> 00:01:22.103 The first thing we're going to do 33 00:01:22.103 --> 00:01:24.400 is create a separate Python file 34 00:01:24.400 --> 00:01:28.660 to host the logic that interacts with our data store. 35 00:01:28.660 --> 00:01:30.500 At the moment, as I said, this is going to be a list, 36 00:01:30.500 --> 00:01:32.310 later on it will be a database. 37 00:01:32.310 --> 00:01:34.190 So I'm going to open my file viewer there, 38 00:01:34.190 --> 00:01:37.500 create a new file called database.py. 39 00:01:37.500 --> 00:01:39.700 Then I'm going to close the file viewer. 40 00:01:39.700 --> 00:01:43.000 Here, we're going to create our entries list, 41 00:01:43.000 --> 00:01:44.910 which is this empty list initially. 42 00:01:44.910 --> 00:01:47.530 And now we're going to create a couple of functions 43 00:01:47.530 --> 00:01:50.400 just to allow us to add a new entry, 44 00:01:50.400 --> 00:01:52.053 or view existing entries. 45 00:01:54.100 --> 00:01:56.320 So here is the add_entry function. 46 00:01:56.320 --> 00:02:00.460 Notice I've used the pass keyword, which means do nothing, 47 00:02:00.460 --> 00:02:04.340 to allow Python to still process this function as valid, 48 00:02:04.340 --> 00:02:07.510 it does need the indented block in there to be valid. 49 00:02:07.510 --> 00:02:09.730 But at the moment, this function does nothing. 50 00:02:09.730 --> 00:02:12.580 And we're going to do something similar for view_entries, 51 00:02:14.350 --> 00:02:15.910 with pass as well. 52 00:02:15.910 --> 00:02:17.550 So now we've got our two functions, 53 00:02:17.550 --> 00:02:21.340 we could go into app.py and import these functions. 54 00:02:21.340 --> 00:02:24.363 And that is what we will do, indeed, in just a moment. 55 00:02:25.210 --> 00:02:29.010 To begin with, we're going to use this add_entry function 56 00:02:29.010 --> 00:02:31.690 to ask the user for what they've learned 57 00:02:31.690 --> 00:02:35.393 and when they learned it, and add that to the entries list. 58 00:02:38.100 --> 00:02:40.700 So we will create this entry content variable, 59 00:02:40.700 --> 00:02:42.200 which is going to be an input 60 00:02:42.200 --> 00:02:44.523 of what have you learned today, 61 00:02:45.730 --> 00:02:47.170 and also the entry date, 62 00:02:47.170 --> 00:02:51.380 which is another input of enter the date. 63 00:02:51.380 --> 00:02:53.620 So here, we've got two strings. 64 00:02:53.620 --> 00:02:56.220 The date is not being validated or anything like that, 65 00:02:56.220 --> 00:02:59.050 as we spoke about earlier on in the presentation, 66 00:02:59.050 --> 00:03:00.120 and what have you learned today, 67 00:03:00.120 --> 00:03:03.020 the user can enter anything they want. 68 00:03:03.020 --> 00:03:04.970 Now that we've got those two pieces of data, 69 00:03:04.970 --> 00:03:06.960 we can create a dictionary with them. 70 00:03:06.960 --> 00:03:09.410 And the dictionary should have a content key 71 00:03:09.410 --> 00:03:11.240 that is going to be the entry_content, 72 00:03:11.240 --> 00:03:14.840 and a date key, which is the entry_date. 73 00:03:14.840 --> 00:03:16.230 Now creating the dictionary on its own, 74 00:03:16.230 --> 00:03:18.380 of course, it's not going to put it into the list. 75 00:03:18.380 --> 00:03:20.740 So we do have to do that ourselves. 76 00:03:20.740 --> 00:03:24.730 Entries.append, and we will add it in there. 77 00:03:24.730 --> 00:03:26.360 So here we can see that we are appending 78 00:03:26.360 --> 00:03:27.340 into the entries list, 79 00:03:27.340 --> 00:03:30.250 our new dictionary that we create here. 80 00:03:30.250 --> 00:03:33.980 To view the entries, we can similarly go through the list 81 00:03:33.980 --> 00:03:36.290 and print out each entry information. 82 00:03:36.290 --> 00:03:38.630 So we can do for entry in entries, 83 00:03:38.630 --> 00:03:41.720 here this for loop creates the entry variable 84 00:03:41.720 --> 00:03:45.020 every time we go through one item of the entries list. 85 00:03:45.020 --> 00:03:46.280 And the entry variable initially 86 00:03:46.280 --> 00:03:48.960 will be the first item in the entries list. 87 00:03:48.960 --> 00:03:52.550 We will then run this indented block of code here. 88 00:03:52.550 --> 00:03:53.383 We will go back, 89 00:03:53.383 --> 00:03:56.060 and entry will become the second item in the entries list, 90 00:03:56.060 --> 00:03:58.860 and then we will run this block of code, and so on. 91 00:03:58.860 --> 00:04:00.790 Again, this is all covered in the Python refresher. 92 00:04:00.790 --> 00:04:02.480 So if you have any questions about for loops, 93 00:04:02.480 --> 00:04:04.560 or dictionaries, or lists, and things like that, 94 00:04:04.560 --> 00:04:06.060 do go back and check that out. 95 00:04:07.260 --> 00:04:09.500 Now, for every entry in the entries list, 96 00:04:09.500 --> 00:04:11.450 we want to print out the information. 97 00:04:11.450 --> 00:04:14.140 So we're going to say print, and then in an f string, 98 00:04:14.140 --> 00:04:17.053 we're going to put the entry, date. 99 00:04:18.230 --> 00:04:19.970 And then in a new line, 100 00:04:19.970 --> 00:04:22.573 we're going to put to the entry content. 101 00:04:23.860 --> 00:04:26.310 And then we're going to put two new lines. 102 00:04:26.310 --> 00:04:27.660 So a couple of things going on here, 103 00:04:27.660 --> 00:04:29.640 this f string is a little bit complicated. 104 00:04:29.640 --> 00:04:32.410 We are interpolating into the string, 105 00:04:32.410 --> 00:04:37.100 the value of accessing the date property of the entry. 106 00:04:37.100 --> 00:04:40.340 So notice that here, we're using double quotation marks 107 00:04:40.340 --> 00:04:42.230 at the end and the start of the string. 108 00:04:42.230 --> 00:04:45.090 The access of the data property in the dictionary 109 00:04:45.090 --> 00:04:47.220 must use single quotation marks, 110 00:04:47.220 --> 00:04:48.650 otherwise, Python would get confused 111 00:04:48.650 --> 00:04:51.420 and it would think that and this is a string, 112 00:04:51.420 --> 00:04:53.630 and this is another one, it doesn't like that. 113 00:04:53.630 --> 00:04:55.920 So make sure to use single quotation marks there. 114 00:04:55.920 --> 00:04:57.860 That's the date of the entry. 115 00:04:57.860 --> 00:05:00.960 Then we're putting a new line with a backslash n character, 116 00:05:00.960 --> 00:05:02.980 and then we're interpolating the content 117 00:05:02.980 --> 00:05:05.080 into it's a new line, 118 00:05:05.080 --> 00:05:06.800 and finally, we're putting two new lines there, 119 00:05:06.800 --> 00:05:08.240 so that when we print the next entry, 120 00:05:08.240 --> 00:05:10.470 there's going to be a bit of separation between the two. 121 00:05:10.470 --> 00:05:14.040 Okay, so now we're going to save this file, 122 00:05:14.040 --> 00:05:16.780 and we can go ahead and use it in our app.py. 123 00:05:16.780 --> 00:05:19.340 So make sure to save it, we can go over to app.py, 124 00:05:19.340 --> 00:05:21.440 and now we can import those two functions 125 00:05:21.440 --> 00:05:24.910 that allow us to interact with our data store in here. 126 00:05:24.910 --> 00:05:28.617 So we do from database import add_entry, and view_entries. 127 00:05:30.100 --> 00:05:33.370 Now once we've got that, we can go down into our menu 128 00:05:33.370 --> 00:05:36.070 and just use them instead of print adding and viewing. 129 00:05:36.070 --> 00:05:38.980 So we'll do add_entry here, make sure to call the function, 130 00:05:38.980 --> 00:05:41.590 and view_entries in here. 131 00:05:41.590 --> 00:05:43.670 Now if we save this and run it, 132 00:05:43.670 --> 00:05:45.080 you'll see that it all works. 133 00:05:45.080 --> 00:05:46.977 So I'm going to open up the terminal down here. 134 00:05:46.977 --> 00:05:48.840 I'm just going to make it a little bit bigger. 135 00:05:48.840 --> 00:05:50.040 I know the text here is a bit small, 136 00:05:50.040 --> 00:05:52.490 but hopefully you can read it there. 137 00:05:52.490 --> 00:05:55.000 And now I'm going to run Python3.8 app.py. 138 00:05:55.000 --> 00:05:56.960 Remember, we've used the walrus operator, 139 00:05:56.960 --> 00:05:58.050 or the assignment expression, 140 00:05:58.050 --> 00:06:00.363 so we need Python 3.8 for this code. 141 00:06:01.580 --> 00:06:02.920 Here we've got our menu, 142 00:06:02.920 --> 00:06:05.250 we can then add a new entry, for example. 143 00:06:05.250 --> 00:06:07.150 And when we type one, of course, 144 00:06:07.150 --> 00:06:09.630 we are running the add_entry code, 145 00:06:09.630 --> 00:06:11.450 that's taken us to database.py, 146 00:06:11.450 --> 00:06:14.250 and now we are currently on this line. 147 00:06:14.250 --> 00:06:15.260 So what have we learned today? 148 00:06:15.260 --> 00:06:19.723 We've learned how to use Python lists as a data store, 149 00:06:20.640 --> 00:06:23.690 and enter the date, the date can be today. 150 00:06:23.690 --> 00:06:25.520 Notice that there is no validation on this date, 151 00:06:25.520 --> 00:06:27.540 so we can enter whatever we want. 152 00:06:27.540 --> 00:06:30.180 Now, every one of you entries, we enter two 153 00:06:30.180 --> 00:06:32.270 and then we get today, 154 00:06:32.270 --> 00:06:35.570 and then a new line, we get the content of the entry. 155 00:06:35.570 --> 00:06:37.230 And then we get two new lines. 156 00:06:37.230 --> 00:06:39.600 And then we would get the next one if there was more, 157 00:06:39.600 --> 00:06:41.530 but now we just get the menu. 158 00:06:41.530 --> 00:06:43.800 Finally, we can enter three to exit. 159 00:06:43.800 --> 00:06:47.240 Okay, just gonna make that a bit smaller again. 160 00:06:47.240 --> 00:06:51.030 And I'm going to clear it which gets rid of all that text. 161 00:06:51.030 --> 00:06:53.040 Now there is a glaring problem 162 00:06:53.040 --> 00:06:55.070 in the way we've structured this application. 163 00:06:55.070 --> 00:06:58.670 And this problem may not be all that obvious 164 00:06:58.670 --> 00:07:00.770 if you are not that familiar with coding, 165 00:07:00.770 --> 00:07:02.840 but I'll tell you that it is a glaring problem 166 00:07:02.840 --> 00:07:04.800 for any developer that's a bit more experienced. 167 00:07:04.800 --> 00:07:08.610 The problem is that the database.py file 168 00:07:08.610 --> 00:07:10.510 is doing really two things. 169 00:07:10.510 --> 00:07:13.110 The database.py file is interacting with the user, 170 00:07:13.110 --> 00:07:16.930 gathering data and it's also storing data in a database. 171 00:07:16.930 --> 00:07:19.240 So it's doing these two separate things. 172 00:07:19.240 --> 00:07:22.400 And it can become confusing and complicated 173 00:07:22.400 --> 00:07:24.800 to then change the data that we're storing, 174 00:07:24.800 --> 00:07:26.270 or how we're gathering it. 175 00:07:26.270 --> 00:07:30.280 It's usually better to have these two things separated, 176 00:07:30.280 --> 00:07:32.540 have one part of our application 177 00:07:32.540 --> 00:07:33.940 dealing with getting the user input, 178 00:07:33.940 --> 00:07:35.380 and have a different part dealing with 179 00:07:35.380 --> 00:07:37.150 interacting with a data store. 180 00:07:37.150 --> 00:07:39.220 Similarly, the view_entries function 181 00:07:39.220 --> 00:07:42.190 is retrieving data from the data store, 182 00:07:42.190 --> 00:07:44.550 and it's also outputting data to the user. 183 00:07:44.550 --> 00:07:47.130 So it's doing those two separate things as well. 184 00:07:47.130 --> 00:07:50.220 Overall, this file here, gets data, 185 00:07:50.220 --> 00:07:52.420 processes data, and displays data. 186 00:07:52.420 --> 00:07:55.610 So yeah, it's not a great file at the moment, 187 00:07:55.610 --> 00:07:56.910 but we can make it better. 188 00:07:57.900 --> 00:08:00.850 Up until before we made this database.py file, 189 00:08:00.850 --> 00:08:04.280 the app.py was in charge of dealing with user input, 190 00:08:04.280 --> 00:08:06.490 and displaying information. 191 00:08:06.490 --> 00:08:07.810 So why don't we keep it that way, 192 00:08:07.810 --> 00:08:10.080 we will move all the user input gathering 193 00:08:10.080 --> 00:08:12.410 and data display to app.py. 194 00:08:12.410 --> 00:08:14.140 And we will keep database.py 195 00:08:14.140 --> 00:08:17.070 as only dealing with the database. 196 00:08:17.070 --> 00:08:20.030 So how to do that is we're going to move these two inputs 197 00:08:20.030 --> 00:08:22.200 over to app.py. 198 00:08:22.200 --> 00:08:25.940 And we're going to pass their contents to add_entry. 199 00:08:25.940 --> 00:08:29.140 So I'm going to add two new parameters here, 200 00:08:29.140 --> 00:08:31.820 entry_content and entry_date. 201 00:08:31.820 --> 00:08:35.230 And now, this function here is only concerned 202 00:08:35.230 --> 00:08:37.150 with taking whatever data it receives 203 00:08:37.150 --> 00:08:39.010 and putting it in a database. 204 00:08:39.010 --> 00:08:42.060 It is going to be app.py going over there now, 205 00:08:42.060 --> 00:08:45.030 that is going to ask the user for data. 206 00:08:45.030 --> 00:08:47.400 And then it's going to call the add_entry function 207 00:08:47.400 --> 00:08:51.760 with the content and the date, just like that. 208 00:08:51.760 --> 00:08:54.150 So now we're getting the user input, 209 00:08:54.150 --> 00:08:55.590 storing it in a variable, 210 00:08:55.590 --> 00:08:58.560 passing the value of that variable to add entry, 211 00:08:58.560 --> 00:09:01.040 and then add_entry is receiving that value 212 00:09:01.040 --> 00:09:02.723 and storing it in the database. 213 00:09:04.330 --> 00:09:06.610 Similarly, if we go to database.py, 214 00:09:06.610 --> 00:09:08.690 we've got here this for entry in entries 215 00:09:08.690 --> 00:09:10.160 that is displaying information. 216 00:09:10.160 --> 00:09:12.540 Instead of that, we're just going to make view_entries 217 00:09:12.540 --> 00:09:16.060 responsible for getting the data from this list, 218 00:09:16.060 --> 00:09:18.100 and giving it back to the caller, 219 00:09:18.100 --> 00:09:21.510 whoever will use this function, so we'll do return entries. 220 00:09:21.510 --> 00:09:23.760 At the moment, this may not seem all that useful. 221 00:09:23.760 --> 00:09:25.700 But later on when we're actually interacting 222 00:09:25.700 --> 00:09:28.830 with a database, you'll see why this becomes more important. 223 00:09:28.830 --> 00:09:30.510 And I've copied the for loop there. 224 00:09:30.510 --> 00:09:32.980 And I'm just going to move it down here 225 00:09:32.980 --> 00:09:34.450 for entry in entries there. 226 00:09:34.450 --> 00:09:37.250 And I'm going to get to the return value of view_entries 227 00:09:37.250 --> 00:09:39.590 and put it in a variable as well. 228 00:09:39.590 --> 00:09:42.700 Notice that you could grab this function here 229 00:09:42.700 --> 00:09:44.650 and put it directly in the for loop, 230 00:09:44.650 --> 00:09:48.860 that's totally fine as well, either option works. 231 00:09:48.860 --> 00:09:51.550 Now notice that the function is called view entries, 232 00:09:51.550 --> 00:09:53.550 which suggests that you're going to be able 233 00:09:53.550 --> 00:09:56.600 to see something, but the view_entries function 234 00:09:56.600 --> 00:10:00.130 is no longer concerned with actually displaying data, 235 00:10:00.130 --> 00:10:04.109 so we're actually going to rename it to get_entries instead. 236 00:10:04.109 --> 00:10:07.280 So we do have to rename it in database.py down here 237 00:10:07.280 --> 00:10:09.293 and in the import as well. 238 00:10:10.300 --> 00:10:13.690 This makes app.py more complicated. 239 00:10:13.690 --> 00:10:15.610 But it makes the whole application simpler 240 00:10:15.610 --> 00:10:19.090 because now reading app.py, we can have a clear idea 241 00:10:19.090 --> 00:10:21.390 of what database.py is doing. 242 00:10:21.390 --> 00:10:23.720 It adds and gets entries from a data store. 243 00:10:23.720 --> 00:10:25.289 And we've also made it clear exactly 244 00:10:25.289 --> 00:10:27.580 what data we're adding to the database, 245 00:10:27.580 --> 00:10:30.630 previously, that was hidden inside database.py 246 00:10:30.630 --> 00:10:31.630 we're calling the function, 247 00:10:31.630 --> 00:10:34.000 and we didn't really know by reading this, 248 00:10:34.000 --> 00:10:37.910 whether database.py was asking for two pieces of data or 10. 249 00:10:37.910 --> 00:10:39.520 Now it's a bit clearer. 250 00:10:39.520 --> 00:10:41.220 And app.py as you read through it, 251 00:10:41.220 --> 00:10:44.880 you can see exactly what the user is going to see as well. 252 00:10:44.880 --> 00:10:47.900 We could improve the code inside app.py a bit further 253 00:10:47.900 --> 00:10:49.890 by splitting it into functions. 254 00:10:49.890 --> 00:10:52.670 So this stuff here could go into its own function., 255 00:10:52.670 --> 00:10:54.680 this stuff here could go into its own function. 256 00:10:54.680 --> 00:10:57.110 We're going to do that just now as well. 257 00:10:57.110 --> 00:10:59.780 We need to define functions before they're used, 258 00:10:59.780 --> 00:11:01.250 so we're going to go up here 259 00:11:01.250 --> 00:11:05.950 and create a prompt_new_entry function. 260 00:11:05.950 --> 00:11:08.860 And this is going to do all of this stuff. 261 00:11:08.860 --> 00:11:11.330 So I'm going to copy that into that. 262 00:11:11.330 --> 00:11:15.283 And down in here, we're just going to call prompt_new_entry. 263 00:11:16.670 --> 00:11:19.500 So I prefix these functions with prompt 264 00:11:19.500 --> 00:11:21.310 because they're actually interacting with the user, 265 00:11:21.310 --> 00:11:23.260 I like to make that a bit clear. 266 00:11:23.260 --> 00:11:25.460 And then we're going to create another function 267 00:11:25.460 --> 00:11:26.480 for viewing entries, 268 00:11:26.480 --> 00:11:29.150 and this time it is going to be called view_entries. 269 00:11:29.150 --> 00:11:33.140 But I'm going to make it take in the entries 270 00:11:33.140 --> 00:11:35.540 from the database itself. 271 00:11:35.540 --> 00:11:39.000 Then this one here is just going to go through the entries 272 00:11:40.090 --> 00:11:41.670 and print them out. 273 00:11:41.670 --> 00:11:43.320 Now when we've got the entries, 274 00:11:43.320 --> 00:11:45.622 we can just call it view_entries 275 00:11:45.622 --> 00:11:48.520 with the entries list that we got from the database. 276 00:11:48.520 --> 00:11:51.180 Now this is starting to become a little bit too superfluous, 277 00:11:51.180 --> 00:11:52.220 this entries database, 278 00:11:52.220 --> 00:11:54.440 so I'm just going to copy that and put it in there, 279 00:11:54.440 --> 00:11:56.430 get rid of that variable. 280 00:11:56.430 --> 00:11:59.210 So while this code is now a bit longer than before, 281 00:11:59.210 --> 00:12:02.920 it is a bit simpler because it's more divided into parts. 282 00:12:02.920 --> 00:12:04.030 When you read this function, 283 00:12:04.030 --> 00:12:06.410 you know that we're going to be adding a new entry. 284 00:12:06.410 --> 00:12:07.790 And when you view this one, 285 00:12:07.790 --> 00:12:10.100 you know we're going to be displaying entry information. 286 00:12:10.100 --> 00:12:12.310 And finally, the loop now is very simple. 287 00:12:12.310 --> 00:12:14.810 If the user input is one, then we prompt for a new entry. 288 00:12:14.810 --> 00:12:17.460 And if it's two, then we view the entries. 289 00:12:17.460 --> 00:12:19.150 So hopefully you agree with that. 290 00:12:19.150 --> 00:12:20.420 Now, in the next few videos, 291 00:12:20.420 --> 00:12:24.030 we're going to be replacing the Python lists for SQL Lite. 292 00:12:24.030 --> 00:12:26.200 So let's go and do that in the next video. 293 00:12:26.200 --> 00:12:27.150 I'll see you there.