WEBVTT 0 00:00.230 --> 00:06.320 Previously, we saw how the len() function gives us a TypeError when we give it a number instead of 1 00:06.320 --> 00:07.160 a string. 2 00:07.280 --> 00:11.330 So let's talk a little bit more about data types and functions. 3 00:11.480 --> 00:17.600 And the way I think about functions is kind of like some sort of fancy machine that you might see in 4 00:17.600 --> 00:18.440 a factory. 5 00:18.440 --> 00:18.800 Right? 6 00:18.800 --> 00:24.530 So in this case, we've got some sort of machine that's going to take potatoes into chips, and we don't 7 00:24.530 --> 00:28.970 really care how it does it, but it's probably going to have to peel the potatoes, wash the potatoes, 8 00:28.970 --> 00:34.920 cut it up, fry it, and then finally return it to us as an output in the form of fries. 9 00:35.100 --> 00:41.070 And if this is the first time that you're watching one of my tutorials, this is probably a health 10 00:41.070 --> 00:41.670 warning, 11 00:41.670 --> 00:43.290 I talk about food a lot. 12 00:43.410 --> 00:47.250 So be prepared if you haven't eaten. 13 00:47.430 --> 00:53.730 Now, let's say that we took the same machine that normally processes potatoes, and we decide to give 14 00:53.740 --> 00:59.410 it a rock, and we just pass this through the function, then we're going to get an error. 15 00:59.410 --> 00:59.980 Right? 16 00:59.980 --> 01:02.290 This is basically what happened here. 17 01:02.290 --> 01:06.760 This len() function doesn't like working with integers, 18 01:06.760 --> 01:13.480 and by forcing this through we end up with an error and our code breaks and it gives us this thing, a 19 01:13.480 --> 01:14.470 TypeError. 20 01:14.470 --> 01:20.530 Now if we hover over this yellow warning we also get the explanation here. 21 01:20.530 --> 01:27.190 Expected type...something called, 'Sized', and got 'int' or an integer instead. 22 01:27.190 --> 01:33.160 So this is already pretty clear where our mistake is even before we hit Run. 23 01:33.160 --> 01:40.390 And the other helpful thing is, when you hover over any function in PyCharm, it gives you the definition 24 01:40.390 --> 01:40.900 of it, 25 01:40.900 --> 01:46.380 and in between the brackets, you can see the data type that that function expects. 26 01:46.380 --> 01:51.840 So the len() function expects a data type with something that's called, Sized. 27 01:51.840 --> 01:59.580 And we can actually click on this link to see the documentation on docs.python.org, which is the official 28 01:59.580 --> 02:01.080 Python documentation. 29 02:01.080 --> 02:07.230 Now I know previously I told you to try using something like W3Schools or using StackOverflow, and 30 02:07.230 --> 02:15.600 the reason is because the documentation from the official Python organization is very, very short. 31 02:15.600 --> 02:18.480 So sometimes it can be enough, 32 02:18.480 --> 02:26.160 but very often I find that it's helpful to find another source to back up this very, very brief explanation. 33 02:26.910 --> 02:30.690 But in our case, in this situation, it does help us. 34 02:30.690 --> 02:37.220 For example, it tells us that len() will return the length, which is the number of items of an object, 35 02:37.220 --> 02:44.900 and the argument, which is what you put in between the brackets may be a sequence such as a string, 36 02:44.900 --> 02:50.480 byte, tuple, list or range, or a collection such as a dictionary set or frozen set. 37 02:50.510 --> 02:54.680 Don't worry about these other data types that we haven't come across yet. 38 02:54.680 --> 02:59.630 We're going to come across them in due time and we're going to be learning all about them. 39 02:59.630 --> 03:03.560 But for now, you already see one that you recognize which is string. 40 03:03.560 --> 03:05.120 So it can take string, 41 03:05.120 --> 03:11.780 but nowhere in this list does it say it can take an integer or any other number data type. 42 03:13.820 --> 03:21.620 So as the first pause exercise, I want you to fix this len() function so that we actually give it data 43 03:21.620 --> 03:23.390 type that it recognizes. 44 03:23.390 --> 03:28.700 And we fix this TypeError so that when we run it, it works as expected. 45 03:28.700 --> 03:32.750 And you can put anything in there as long as it gets rid of the warnings and errors. 46 03:32.750 --> 03:34.040 Pause the video now. 47 03:35.720 --> 03:36.170 All right. 48 03:36.170 --> 03:37.850 This should be relatively easy. 49 03:37.850 --> 03:44.240 We can change this to any string, which we already know is a data type that this function can accept. 50 03:44.240 --> 03:49.180 So we can simply change it to "Hello" or whichever string you can think of. 51 03:49.180 --> 03:54.760 And now when we hit run, all our errors and warnings should now go away. 52 03:54.760 --> 04:01.780 If you see something like "PEP 8 blank line at end of file," and it bothers you, don't worry about it too 53 04:01.780 --> 04:02.110 much, 54 04:02.110 --> 04:09.220 but it's basically saying that in an ideal situation, a Python file should only have one blank line 55 04:09.220 --> 04:10.270 at the very bottom. 56 04:10.270 --> 04:15.190 So if I hit Run again, that will clear up that warning. For everybody out there who has a little bit 57 04:15.190 --> 04:18.010 of OCD like me, this can be a lifesaver. 58 04:18.820 --> 04:27.670 So now that we've seen that in Python, each function expects to work with a specific set of data types, 59 04:27.670 --> 04:34.860 so there's only certain data types that can go into the parentheses of a particular function. 60 04:34.890 --> 04:36.540 Now here comes the question, 61 04:36.540 --> 04:41.940 "Well, how would we know what data type a particular piece of data has?" 62 04:41.940 --> 04:44.940 So how would we know what is the data type of 63 04:44.940 --> 04:45.510 "Hello"? 64 04:45.510 --> 04:49.680 Well it's very easy to visually see it because it has the double quotes around it, 65 04:49.680 --> 04:55.080 and anything with double quotes around it, even if it's a number, is in fact a string. 66 04:55.320 --> 05:03.390 But there is also one function in Python that allows us to check the data type of any piece of data 67 05:03.390 --> 05:04.380 or variable. 68 05:04.380 --> 05:08.400 So all we need to do is to use the keyword "type", 69 05:08.400 --> 05:12.480 and then in between the parentheses we can put in any piece of data. 70 05:12.480 --> 05:14.460 It can accept any data type. 71 05:14.460 --> 05:18.570 And then it will give us in return the data type. 72 05:18.570 --> 05:25.550 But as always in order to see it we have to wrap this inside a set of parentheses and use the print 73 05:25.550 --> 05:29.120 statement to put this into the output area. 74 05:29.120 --> 05:30.350 So let's run that. 75 05:30.350 --> 05:35.030 And you can see it tells us that this is something called a class 'str'. 76 05:35.030 --> 05:39.920 So this is basically saying it checked the data type of this piece of data 77 05:39.920 --> 05:40.640 we gave it, 78 05:40.640 --> 05:45.500 and it told us that it's actually a string which is what we expected as well. 79 05:45.500 --> 05:48.320 So we can do this with various different data types. 80 05:48.320 --> 05:49.880 Let's check it with the number. 81 05:49.880 --> 05:52.400 Well in this case we gave it a whole number, 82 05:52.400 --> 05:53.780 so no decimal places. 83 05:53.780 --> 05:56.000 And it told us it's an integer. 84 05:56.000 --> 05:59.570 We could do this with floats with booleans, 85 05:59.570 --> 06:04.700 and it will always very, very helpfully tell us what is the data type. 86 06:04.700 --> 06:07.490 And this is something called type checking. 87 06:07.670 --> 06:10.760 So now it's time for another quick pause 88 06:10.760 --> 06:13.340 check to make sure you understood what's going on. 89 06:13.340 --> 06:21.110 I want you to write out four lines of code to print out the four different data types that we have already 90 06:21.110 --> 06:22.010 learned about. 91 06:22.010 --> 06:27.230 So it's going to be the string, the integer, the float, and the boolean. 92 06:27.230 --> 06:33.680 And we want all four of these printed out in four lines in the output area, using what you've learned 93 06:33.680 --> 06:40.090 and the correct data type to put in inside the parentheses before the type check. 94 06:40.090 --> 06:42.700 So pause the video now and give this a go. 95 06:46.150 --> 06:49.690 All right so we've got already the integer type. 96 06:49.690 --> 06:53.200 So let's put the string one above it. 97 06:53.560 --> 06:58.750 And we know that all strings go inside a set of double quotes. 98 06:58.750 --> 07:01.750 And then we want a floating point number. 99 07:01.750 --> 07:05.530 So we could do a 3.14. 100 07:05.530 --> 07:12.910 And finally, we want a boolean type which we know is either True or False with a capital T and capital 101 07:12.910 --> 07:13.390 F. 102 07:13.390 --> 07:17.890 So now if I hit Run, we should see class str, int, float and bool. 103 07:17.890 --> 07:25.650 The full collection of all the major primitive Python data types that we learned about in the last lesson. 104 07:25.650 --> 07:31.590 If that was confusing at all, review the last lesson and hopefully this all makes perfect sense. 105 07:32.550 --> 07:37.230 Now what if we aren't happy with the assigned data type? 106 07:37.260 --> 07:42.330 What if we want to convert a piece of data into a different data type? 107 07:42.330 --> 07:48.030 Well, then we would need to learn about something called type conversion, also known as type casting 108 07:48.030 --> 07:49.020 in Python. 109 07:49.020 --> 07:53.550 So let's go ahead and clear the board to make this less confusing. 110 07:53.550 --> 07:56.850 And let's start out with a very simple string. 111 07:56.850 --> 08:03.180 So we all know that this is a string because it's enclosed in a set of double quotes. 112 08:03.180 --> 08:07.320 But what if I wanted to turn it into an integer? 113 08:07.320 --> 08:16.640 Well, I can use one of the built-in functions called "int" and I can convert this into a number. 114 08:17.030 --> 08:25.760 So whereas previously we saw that if we tried to print the string "123" + "456", 115 08:25.760 --> 08:31.460 then we would end up with 1, 2, 3, 4, 5, 6. 116 08:31.460 --> 08:40.730 And because both of these pieces of data are string data types, the plus sign does concatenation instead 117 08:40.730 --> 08:43.700 of maths and adding these two together. 118 08:43.700 --> 08:50.960 But now that we've converted this 1, 2, 3 into an integer, you can see that if we replace 119 08:50.960 --> 08:59.240 this string with this type casted integer and we could do the same for 4, 5, 6. 120 08:59.240 --> 09:05.630 Now if I hit Run, you'll see that it actually treats them as numbers and adds them together. 121 09:05.630 --> 09:08.840 So this is the power of type conversion. 122 09:08.840 --> 09:16.370 Now, one of the dangerous things about this is of course sometimes you can't convert things into a 123 09:16.370 --> 09:17.600 different data type. 124 09:17.690 --> 09:26.090 For example, if I tried to convert, "ABC" into a number, well, that doesn't really make sense. 125 09:26.090 --> 09:30.100 If I gave that to you, what would ABC be as a number? 126 09:30.100 --> 09:30.910 I don't know. 127 09:30.910 --> 09:35.740 So if we run this, you can see we get something called a ValueError. 128 09:35.740 --> 09:40.600 So I hope you're collecting these errors in a notebook somewhere because we're coming across lots of 129 09:40.600 --> 09:40.930 them, 130 09:40.930 --> 09:45.010 and you will come across more in your lifetime as a Python developer. 131 09:45.100 --> 09:55.120 So this is saying that there is an invalid literal for the int, which is ABC, and so it doesn't really 132 09:55.120 --> 09:58.840 make sense to convert this into a number is what it's trying to tell you. 133 09:58.870 --> 10:04.300 So you have to be really careful when you're doing type conversions because sometimes you can end 134 10:04.300 --> 10:08.350 up with errors and sometimes you can just simply lose data. 135 10:08.350 --> 10:14.500 But we can use this method to convert things into all of the four major primitive types that we've learned 136 10:14.500 --> 10:21.210 about. So we can convert to an integer, we can convert into a float, we can convert into a string, 137 10:21.210 --> 10:24.780 and we can even convert into a bool. 138 10:26.100 --> 10:33.030 So to check that you've understood how to convert between different data types and why we get different 139 10:33.030 --> 10:40.260 type errors, I have a final pause challenge for you, which is to make this line of code run without 140 10:40.260 --> 10:40.830 errors. 141 10:40.830 --> 10:46.770 So I want you to go ahead and copy this line of code, paste it into your code file, and try to hit run. 142 10:46.770 --> 10:55.740 Now go ahead and enter a name triggered by this input, and then you will see that you get a TypeError. 143 10:55.740 --> 10:57.810 So read through the TypeError, 144 10:57.840 --> 11:03.600 see if you can understand what it's trying to tell you, and fix this code so that it does what you 145 11:03.600 --> 11:09.920 expect it to do, which is to print out the number of letters in the name that the user submits into 146 11:09.920 --> 11:10.610 the input. 147 11:10.640 --> 11:11.900 Pause the video. 148 11:11.900 --> 11:12.830 Give this a go. 149 11:17.150 --> 11:17.750 All right. 150 11:17.750 --> 11:24.140 So in order to break this problem down, let's use some variables to simplify things and make it easier 151 11:24.140 --> 11:24.770 to read. 152 11:24.770 --> 11:32.720 Let's take this second part of this print statement, and let's take it out into separate variables. 153 11:32.720 --> 11:42.320 So we know that we can get the name_of_the_user by using this input() function, 154 11:42.620 --> 11:48.170 and I'm making these variable names extra wordy just so that when you read it, it makes it a little 155 11:48.170 --> 11:49.250 bit more sense. 156 11:49.250 --> 11:54.240 And I'm actually going to delete the rest of this as well, just to make everything easy to read. 157 11:54.270 --> 12:00.120 So next we need the length_of_name, 158 12:01.320 --> 12:05.580 and this is done by using the len() function, 159 12:05.580 --> 12:09.720 and we pass in the name of the user that we got from line one. 160 12:09.870 --> 12:16.980 So now finally, what we have here is the length of the name which we want to tag to the end of this print 161 12:16.990 --> 12:17.800 statement. 162 12:17.830 --> 12:20.740 Now what is this error trying to tell us? 163 12:20.740 --> 12:28.930 It's saying you can only concatenate string to a string, not an integer, which is what it sees in 164 12:28.930 --> 12:30.730 this line of code. 165 12:30.730 --> 12:32.740 So where is the integer? 166 12:32.740 --> 12:38.920 Well, we know that when we calculate the length of something it gives us a number. 167 12:38.920 --> 12:40.180 It gives us a whole number. 168 12:40.180 --> 12:43.060 So this is probably an integer. 169 12:43.060 --> 12:43.480 well, 170 12:43.480 --> 12:46.510 we can verify this by using a type check. 171 12:46.510 --> 12:46.900 Right? 172 12:46.900 --> 12:50.530 We can print the first part of this concatenation, 173 12:50.530 --> 12:58.960 and we can put it inside a type function to check what is the data type of this first part. 174 12:58.960 --> 13:06.930 And then we can also check the data type of the second part, which is now called, length_of_name. 175 13:07.500 --> 13:09.330 So let's comment this out. 176 13:09.330 --> 13:11.190 Let's go ahead and run this code. 177 13:11.190 --> 13:16.650 Enter a name and you can see the first one is a string and the second one is an integer. 178 13:16.650 --> 13:19.950 So this is a type str, 179 13:19.950 --> 13:22.110 and this is a type int. 180 13:22.110 --> 13:29.190 So now it makes sense that when we're printing, we can't simply concatenate a string to a number, 181 13:29.190 --> 13:30.690 it doesn't know how to do that. 182 13:30.720 --> 13:38.880 So how can we convert this length_of_name into the same data type as this first part, which is a string? 183 13:38.880 --> 13:41.040 Well, you learnt how to do that already. 184 13:41.040 --> 13:50.010 All we need to do is to wrap this inside a set of parentheses, which is the string type conversion. 185 13:50.010 --> 13:53.970 And so now we have this part which is now a string, 186 13:53.970 --> 13:56.420 and then we add it to another string. 187 13:56.420 --> 14:01.490 And now if I run this code again then you'll see that it works without any issues. 188 14:01.490 --> 14:04.700 Number of letters in your name: 6, printed out. 189 14:05.390 --> 14:13.370 So hopefully, this makes sense to you and you'll be able to understand in the future how to do type conversions, 190 14:13.370 --> 14:16.880 and how to understand when you have different type errors 191 14:16.880 --> 14:18.620 what has gone wrong.