1 1 00:00:02,210 --> 00:00:03,900 Let's use regular expressions 2 2 00:00:03,900 --> 00:00:08,060 to find a number within this string here. 3 3 00:00:08,060 --> 00:00:10,653 What to do is I'm going to import RE. 4 4 00:00:11,624 --> 00:00:15,010 And RE is the Python module for regular expressions. 5 5 00:00:15,010 --> 00:00:17,600 The regular expression allows us to 6 6 00:00:17,600 --> 00:00:21,390 define what the structure of a string is, 7 7 00:00:21,390 --> 00:00:24,530 so that we can get some information out of it. 8 8 00:00:24,530 --> 00:00:29,530 So we're gonna say that the pattern is RE dot compile. 9 9 00:00:30,210 --> 00:00:33,170 And then we're gonna use an R string. 10 10 00:00:33,170 --> 00:00:37,550 An R string in Python is used for regular expressions. 11 11 00:00:37,550 --> 00:00:39,405 And essentially, it allows us to define a string 12 12 00:00:39,405 --> 00:00:42,860 that uses regular expression syntax, 13 13 00:00:42,860 --> 00:00:44,570 and Python will sort of help us out 14 14 00:00:44,570 --> 00:00:45,883 with defining the string. 15 15 00:00:46,880 --> 00:00:50,294 Now what we want to do is tell the RE module 16 16 00:00:50,294 --> 00:00:52,010 that what we're looking for 17 17 00:00:52,010 --> 00:00:54,780 has the structure of this thing here, 18 18 00:00:54,780 --> 00:00:59,780 which is a number, a comma, a few numbers, 19 19 00:01:01,560 --> 00:01:05,490 a period, and a few more numbers. 20 20 00:01:05,490 --> 00:01:08,700 So we have that there. 21 21 00:01:08,700 --> 00:01:13,440 What we're gonna do is say backslash D. 22 22 00:01:13,440 --> 00:01:16,023 Backslash D means a number. 23 23 00:01:16,900 --> 00:01:19,270 And then we're gonna type a comma, 24 24 00:01:19,270 --> 00:01:24,180 then we're gonna type backslash D, backslash D, backslash D. 25 25 00:01:24,180 --> 00:01:27,290 Then we're gonna type backslash full stop. 26 26 00:01:27,290 --> 00:01:29,920 And then we're gonna type backslash D, backslash D. 27 27 00:01:29,920 --> 00:01:31,820 And then we're gonna close the brackets. 28 28 00:01:31,820 --> 00:01:35,820 So this is not very good regular expression, 29 29 00:01:35,820 --> 00:01:37,050 but we're gonna improve on it. 30 30 00:01:37,050 --> 00:01:38,968 It just wanna show you how it works first. 31 31 00:01:38,968 --> 00:01:40,823 We've got a number. 32 32 00:01:42,099 --> 00:01:43,540 A number, first of all, here. 33 33 00:01:43,540 --> 00:01:45,000 Then we've got a comma, 34 34 00:01:45,000 --> 00:01:46,940 and this comma does not have a backslash 35 35 00:01:46,940 --> 00:01:50,160 in front of it because the backslash, sorry, the comma 36 36 00:01:50,160 --> 00:01:53,623 doesn't mean anything special in regular expressions. 37 37 00:01:55,090 --> 00:01:57,400 The D has a backslash, 38 38 00:01:57,400 --> 00:02:00,160 because if we don't put the backslash in, 39 39 00:02:00,160 --> 00:02:02,430 what this means is that the first character 40 40 00:02:02,430 --> 00:02:04,600 should be the letter D. 41 41 00:02:04,600 --> 00:02:07,460 Backslash D means it should be a number. 42 42 00:02:07,460 --> 00:02:10,390 This is just regular expression syntax. 43 43 00:02:10,390 --> 00:02:12,820 So after the comma, we have three more numbers, 44 44 00:02:12,820 --> 00:02:14,530 three backslash Ds. 45 45 00:02:14,530 --> 00:02:16,330 And then we have a period. 46 46 00:02:16,330 --> 00:02:21,210 And we use backslash period, because if we don't, 47 47 00:02:21,210 --> 00:02:23,840 then this means that we want the 48 48 00:02:23,840 --> 00:02:26,710 period element in regular expressions. 49 49 00:02:26,710 --> 00:02:28,350 And the period in the regular expression 50 50 00:02:28,350 --> 00:02:32,110 means any character, so a number, a letter, anything else. 51 51 00:02:32,110 --> 00:02:34,530 So, if we don't put the backslash, 52 52 00:02:34,530 --> 00:02:38,360 then we could have one, something like this. 53 53 00:02:38,360 --> 00:02:41,820 These would be valued, if we don't put the backslash in, 54 54 00:02:41,820 --> 00:02:44,943 because this here is any character. 55 55 00:02:45,830 --> 00:02:49,160 If we put the backslash in, this would not be valued. 56 56 00:02:49,160 --> 00:02:51,800 It would have to be a full stop. 57 57 00:02:51,800 --> 00:02:54,873 Then we've got backslash D and backslash D, as well. 58 58 00:02:55,940 --> 00:02:59,960 Now what this means is that if we 59 59 00:02:59,960 --> 00:03:03,000 give the regular expression module 60 60 00:03:03,000 --> 00:03:07,020 this pattern and this value here, 61 61 00:03:07,020 --> 00:03:12,020 it's going to know that a part of this string 62 62 00:03:12,550 --> 00:03:14,690 is in this format. 63 63 00:03:14,690 --> 00:03:16,830 Essentially, it's going to ignore the pound sign 64 64 00:03:16,830 --> 00:03:18,920 because it doesn't really care about it, 65 65 00:03:18,920 --> 00:03:22,010 but it's going to say there is a portion of this string 66 66 00:03:22,010 --> 00:03:24,430 that has this pattern inside it. 67 67 00:03:24,430 --> 00:03:26,580 This number comma, number, number, number, 68 68 00:03:26,580 --> 00:03:28,713 full stop or period, number, number. 69 69 00:03:29,771 --> 00:03:32,778 And that is what the brackets are for. 70 70 00:03:32,778 --> 00:03:35,140 So the brackets are left until the end. 71 71 00:03:35,140 --> 00:03:36,450 What the brackets are going to do 72 72 00:03:36,450 --> 00:03:40,330 is they are going to allow us to tell 73 73 00:03:40,330 --> 00:03:42,790 the regular expression module that we are interested 74 74 00:03:42,790 --> 00:03:45,844 in just this part of the pattern. 75 75 00:03:45,844 --> 00:03:50,844 So then we can extract that as its own separate value. 76 76 00:03:52,333 --> 00:03:56,380 So, I'm gonna explain what that means in just a moment. 77 77 00:03:56,380 --> 00:03:59,610 Let's first find whether there are any matches 78 78 00:03:59,610 --> 00:04:02,970 for this pattern in our string price. 79 79 00:04:02,970 --> 00:04:05,950 The way we do that, we say pattern dot search 80 80 00:04:05,950 --> 00:04:07,883 and then we give it the string price. 81 81 00:04:09,420 --> 00:04:14,123 Okay, and then we're gonna say print match dot group, 82 82 00:04:14,960 --> 00:04:17,950 and then we're gonna give it one inside the brackets. 83 83 00:04:17,950 --> 00:04:22,030 So, let's run this and show you exactly what that does. 84 84 00:04:22,030 --> 00:04:24,300 You can see that it's printed out 85 85 00:04:24,300 --> 00:04:26,710 the thing within the string price 86 86 00:04:26,710 --> 00:04:29,646 that matches the pattern around the brackets. 87 87 00:04:29,646 --> 00:04:33,223 If we don't patient the brackets in, 88 88 00:04:34,060 --> 00:04:36,290 then this doesn't quite work, 89 89 00:04:36,290 --> 00:04:39,160 because we haven't told the regular expression module 90 90 00:04:39,160 --> 00:04:42,339 that we are interested only in this pattern here. 91 91 00:04:42,339 --> 00:04:46,740 Okay, so now what this has done 92 92 00:04:46,740 --> 00:04:48,680 is it's gone into the string price, 93 93 00:04:48,680 --> 00:04:51,430 it's found this pattern inside it, 94 94 00:04:51,430 --> 00:04:53,230 and then because we've got the brackets, 95 95 00:04:53,230 --> 00:04:56,150 it's created what's called a group for us 96 96 00:04:56,150 --> 00:04:59,840 that we can then go and retrieve if it exists. 97 97 00:04:59,840 --> 00:05:01,523 So in this case, it does exist. 98 98 00:05:02,530 --> 00:05:05,348 Now there are a couple of issues with this, though. 99 99 00:05:05,348 --> 00:05:09,700 The first issue is that there are some situations 100 100 00:05:09,700 --> 00:05:13,310 where the comma may not be there. 101 101 00:05:13,310 --> 00:05:15,850 The comma, for example, could be not there 102 102 00:05:15,850 --> 00:05:19,030 if we have a price like 567.95. 103 103 00:05:19,030 --> 00:05:21,630 There is no comma in this price. 104 104 00:05:21,630 --> 00:05:23,060 So what we can do is we can put 105 105 00:05:23,060 --> 00:05:25,990 a question mark directly after the comma 106 106 00:05:25,990 --> 00:05:30,990 and that means this is an optional thing in the string. 107 107 00:05:31,010 --> 00:05:34,470 So it will match whether there's a comma or not. 108 108 00:05:34,470 --> 00:05:37,199 So at the moment, if we have a price like this, 109 109 00:05:37,199 --> 00:05:39,210 it would match this pattern, 110 110 00:05:39,210 --> 00:05:42,260 because we've got a number, then we've got a comma, 111 111 00:05:42,260 --> 00:05:44,120 which is optional, which is not there, 112 112 00:05:44,120 --> 00:05:45,830 and then we've got three more numbers, 113 113 00:05:45,830 --> 00:05:46,960 and then we've got the period, 114 114 00:05:46,960 --> 00:05:49,118 and then we've got two more numbers. 115 115 00:05:49,118 --> 00:05:53,120 Now this pattern would not be valid for something like this, 116 116 00:05:53,120 --> 00:05:54,459 because we've got a number, 117 117 00:05:54,459 --> 00:05:56,740 then we've got a comma which is optional, 118 118 00:05:56,740 --> 00:05:57,670 then we've got two numbers, 119 119 00:05:57,670 --> 00:05:59,495 but we don't have the third number. 120 120 00:05:59,495 --> 00:06:03,440 So this backslash D would be missing. 121 121 00:06:03,440 --> 00:06:04,930 So what are we gonna do? 122 122 00:06:04,930 --> 00:06:09,930 Well, we're going to say that we want at least one number, 123 123 00:06:11,970 --> 00:06:15,113 but it can be any number of numbers. 124 124 00:06:16,580 --> 00:06:20,773 So one or more number is what this plus means. 125 125 00:06:21,740 --> 00:06:23,833 And if we do the same here, 126 126 00:06:24,960 --> 00:06:27,938 then it means we expect at least one number, 127 127 00:06:27,938 --> 00:06:32,070 then a comma, which may or may not be there, 128 128 00:06:32,070 --> 00:06:36,440 then at least one number, so that means two numbers, 129 129 00:06:36,440 --> 00:06:38,410 then we've got a period, 130 130 00:06:38,410 --> 00:06:40,403 and then we've got two more numbers. 131 131 00:06:41,650 --> 00:06:44,870 So this would match something like 15 95 132 132 00:06:44,870 --> 00:06:48,340 or one five eight 95, or indeed any other number 133 133 00:06:48,340 --> 00:06:52,513 that has at least two numbers in front of the period. 134 134 00:06:53,430 --> 00:06:55,030 We need at least two numbers, 135 135 00:06:55,030 --> 00:06:57,610 because we have the backslash D plus, 136 136 00:06:57,610 --> 00:07:00,080 which means one number or more. 137 137 00:07:00,080 --> 00:07:01,810 And we also to have backslash D plus, 138 138 00:07:01,810 --> 00:07:03,500 which means one number or more. 139 139 00:07:03,500 --> 00:07:05,513 So in total we have two numbers or more. 140 140 00:07:07,200 --> 00:07:12,200 So we can turn one of these into essentially 141 141 00:07:12,670 --> 00:07:14,663 zero or more numbers. 142 142 00:07:15,800 --> 00:07:18,363 And the way we do that is with the asterisk. 143 143 00:07:19,380 --> 00:07:24,380 So what this means is we're gonna have one or more number, 144 144 00:07:25,120 --> 00:07:28,990 a comma which is optional, and then zero or more numbers, 145 145 00:07:28,990 --> 00:07:31,290 and then a period, and then two more numbers. 146 146 00:07:31,290 --> 00:07:33,210 So now that we've got our pattern here, 147 147 00:07:33,210 --> 00:07:35,120 this may not be a perfect pattern, 148 148 00:07:35,120 --> 00:07:38,060 it maybe won't work for some currencies 149 149 00:07:38,060 --> 00:07:40,150 that use, for example, the period here 150 150 00:07:40,150 --> 00:07:41,970 and the comma here and so on. 151 151 00:07:41,970 --> 00:07:43,860 But we're not really aiming for perfection 152 152 00:07:43,860 --> 00:07:45,200 at this point in time. 153 153 00:07:45,200 --> 00:07:46,430 We can change this later on. 154 154 00:07:46,430 --> 00:07:48,190 I just wanted to show you a little about 155 155 00:07:48,190 --> 00:07:50,493 how regular expression work. 156 156 00:07:51,390 --> 00:07:52,970 And now that we have this, 157 157 00:07:52,970 --> 00:07:56,990 finding the price as a number is quite straight forward. 158 158 00:07:56,990 --> 00:07:59,993 We're gonna say found price is match group one. 159 159 00:08:00,850 --> 00:08:02,670 And then we're gonna remove the comma. 160 160 00:08:02,670 --> 00:08:04,090 Because as you can see down here, 161 161 00:08:04,090 --> 00:08:06,422 we've got the comma in this string, 162 162 00:08:06,422 --> 00:08:10,880 but we cannot turn this into a number in Python 163 163 00:08:10,880 --> 00:08:11,930 if it still has the comma. 164 164 00:08:11,930 --> 00:08:14,660 So we first have to remove the comma. 165 165 00:08:14,660 --> 00:08:17,040 And we're gonna say without commas is 166 166 00:08:17,040 --> 00:08:18,770 found price dot replace 167 167 00:08:21,480 --> 00:08:26,480 and we're going to give this replace a method two arguments. 168 168 00:08:27,080 --> 00:08:30,010 The first one is the element that we want to replace. 169 169 00:08:30,010 --> 00:08:32,980 The second one is what we want to replace it by. 170 170 00:08:32,980 --> 00:08:34,220 So what this is saying is 171 171 00:08:34,220 --> 00:08:37,550 take the commas and replace them by empty strings. 172 172 00:08:37,550 --> 00:08:39,600 Essentially just gonna delete the commas. 173 173 00:08:40,540 --> 00:08:45,540 And finally, we can say price equal float of without commas. 174 174 00:08:46,580 --> 00:08:48,546 So once we've stripped out the commas, 175 175 00:08:48,546 --> 00:08:51,550 we can turn that into a number in Python, 176 176 00:08:51,550 --> 00:08:53,900 a floating point number, in this case. 177 177 00:08:53,900 --> 00:08:56,533 And at the end, we can print the price. 178 178 00:08:57,470 --> 00:08:58,583 And we can run that. 179 179 00:08:59,530 --> 00:09:00,730 And you can see that now we get 180 180 00:09:00,730 --> 00:09:03,260 one four six nine point zero. 181 181 00:09:03,260 --> 00:09:05,534 No longer it is point zero zero, 182 182 00:09:05,534 --> 00:09:10,534 because Python knows that since you've only got one zero, 183 183 00:09:11,160 --> 00:09:13,770 once you've printed a floating point number, 184 184 00:09:13,770 --> 00:09:15,220 you no longer need the other decimal 185 185 00:09:15,220 --> 00:09:16,330 because it's also going to be zero. 186 186 00:09:16,330 --> 00:09:18,130 It's kina pointless to print it out. 187 187 00:09:19,001 --> 00:09:23,110 So this is how you would use regular expressions 188 188 00:09:23,110 --> 00:09:27,069 to extract the information contained in the string 189 189 00:09:27,069 --> 00:09:28,567 and turn it into a number. 190 190 00:09:28,567 --> 00:09:30,160 And the purpose is, of course, 191 191 00:09:30,160 --> 00:09:32,650 that we can then potentially say 192 192 00:09:32,650 --> 00:09:35,589 is this price under 1,000 pounds? 193 193 00:09:35,589 --> 00:09:38,060 And if it is, we can send the user an email 194 194 00:09:38,060 --> 00:09:39,310 and tell them about it. 195 195 00:09:39,310 --> 00:09:42,230 In this case, it's not, so, but yeah. 196 196 00:09:42,230 --> 00:09:44,470 So that's how the app is going to work. 197 197 00:09:44,470 --> 00:09:46,796 We're going to be doing this inside our app 198 198 00:09:46,796 --> 00:09:49,070 in order to calculate whether 199 199 00:09:49,070 --> 00:09:53,070 a price is under what we want or not. 200 200 00:09:53,070 --> 00:09:55,460 Of course, this is only going to be a small part of the app, 201 201 00:09:55,460 --> 00:09:57,390 but it is the main part. 202 202 00:09:57,390 --> 00:10:00,070 This is really what the app is all about 203 203 00:10:00,070 --> 00:10:02,480 and all the rest of our app is going to be there 204 204 00:10:02,480 --> 00:10:07,480 line:15% to allow users to very easily manage this search. 205 205 00:10:08,550 --> 00:10:10,340 line:15% Alright, so that's everything for this video. 206 206 00:10:10,340 --> 00:10:11,173 line:15% Thank you for joining me. 207 207 00:10:11,173 --> 00:10:12,520 line:15% I hope you've learned something in it. 208 208 00:10:12,520 --> 00:10:13,970 I'll see you in the next one.