1 00:00:04,780 --> 00:00:07,430 Python's got some built-in functions 2 00:00:07,430 --> 00:00:09,309 that can be used as an alternative 3 00:00:09,309 --> 00:00:12,530 to comprehensions. Generally, I suggest using 4 00:00:12,530 --> 00:00:15,170 comprehensions instead, and in fact Guildo 5 00:00:15,170 --> 00:00:17,540 van Rossum wanted to remove map and 6 00:00:17,540 --> 00:00:20,180 filter from Python altogether, but was 7 00:00:20,180 --> 00:00:22,460 instead persuaded to keep them. Now you 8 00:00:22,460 --> 00:00:24,380 can find his reasoning about this at the 9 00:00:24,380 --> 00:00:25,580 link that I've got on the screen there 10 00:00:25,580 --> 00:00:27,770 now, and this link is in the resources 11 00:00:27,770 --> 00:00:29,539 section of the video. This is well worth 12 00:00:29,539 --> 00:00:30,890 a read, even if you're one of those 13 00:00:30,890 --> 00:00:33,440 Python programmers who like to use map. 14 00:00:33,440 --> 00:00:35,510 So we're going to take a look at these 15 00:00:35,510 --> 00:00:37,400 functions, because you need to be 16 00:00:37,400 --> 00:00:38,989 familiar with them in order to 17 00:00:38,989 --> 00:00:41,360 understand code that uses them. So we'll 18 00:00:41,360 --> 00:00:43,820 start with Map, and I'll use an earlier 19 00:00:43,820 --> 00:00:46,370 comprehension example from the course, so 20 00:00:46,370 --> 00:00:48,290 that we can see both methods producing 21 00:00:48,290 --> 00:00:50,900 the same results. We're going to swing 22 00:00:50,900 --> 00:00:52,699 over to IntelliJ and I'm going 23 00:00:52,699 --> 00:00:56,390 to create a new project. Make sure that I 24 00:00:56,390 --> 00:00:58,489 select the right project SDK which will 25 00:00:58,489 --> 00:01:01,760 be the latest version of Python, and I'm 26 00:01:01,760 --> 00:01:06,409 going to call this one map and I'll make 27 00:01:06,409 --> 00:01:07,460 sure I've got it in the right folder 28 00:01:07,460 --> 00:01:16,100 here, Finish, and then we'll create the 29 00:01:16,100 --> 00:01:19,659 actual project, the Python file, as well. 30 00:01:19,659 --> 00:01:21,979 I'm going to call that 31 00:01:21,979 --> 00:01:28,969 map_intro. Okay, then I'm going to paste 32 00:01:28,969 --> 00:01:31,009 this code, that I talked about from an earlier 33 00:01:31,009 --> 00:01:32,869 video in this course, to save a bit of 34 00:01:32,869 --> 00:01:35,840 time, and what I'll do is run the program 35 00:01:35,840 --> 00:01:37,340 to make sure that it actually works. 36 00:01:37,340 --> 00:01:41,359 So I right-click and select Run and you 37 00:01:41,359 --> 00:01:42,979 can see we've now got the results 38 00:01:42,979 --> 00:01:44,090 appearing at the bottom of the screen. 39 00:01:44,090 --> 00:01:46,219 Now this program is using two 40 00:01:46,219 --> 00:01:49,280 comprehensions. The first produces a list 41 00:01:49,280 --> 00:01:50,799 of all the characters in the text, 42 00:01:50,799 --> 00:01:53,659 capitalized. The second produces a list 43 00:01:53,659 --> 00:01:55,789 of all the words in the text, again 44 00:01:55,789 --> 00:01:58,310 capitalized. Alright, so we can do the 45 00:01:58,310 --> 00:02:01,280 same thing with the map function. So what 46 00:02:01,280 --> 00:02:02,299 I'll do is I'll put the corresponding 47 00:02:02,299 --> 00:02:04,909 map code after each one then we'll see 48 00:02:04,909 --> 00:02:06,770 what it's doing. So I come down 49 00:02:06,770 --> 00:02:10,850 here firstly and we'll just make a comment - 50 00:02:10,850 --> 00:02:12,319 the fact that we're using map here - so 51 00:02:12,319 --> 00:02:15,290 use map, and this will be map underscore 52 00:02:15,290 --> 00:02:16,040 capitals 53 00:02:16,040 --> 00:02:17,960 is equal to 54 00:02:17,960 --> 00:02:20,420 list left parentheses map left 55 00:02:20,420 --> 00:02:25,730 parentheses str dot upper comma space 56 00:02:25,730 --> 00:02:28,640 text and then closing off the two, 57 00:02:28,640 --> 00:02:30,290 closing off by selecting the two right 58 00:02:30,290 --> 00:02:32,060 parentheses. Then we'll just print that 59 00:02:32,060 --> 00:02:36,020 out, map underscore capitals. We'll go down 60 00:02:36,020 --> 00:02:38,600 below the second comprehension and put 61 00:02:38,600 --> 00:02:41,690 some map equivalent code, so we'll put a comment 62 00:02:41,690 --> 00:02:43,760 there to that effect - map underscore 63 00:02:43,760 --> 00:02:46,970 words, this time, is equal to list left 64 00:02:46,970 --> 00:02:50,660 parentheses map left parentheses str 65 00:02:50,660 --> 00:02:54,310 dot upper comma space text dot split 66 00:02:54,310 --> 00:02:57,140 parentheses is going to be, two single 67 00:02:57,140 --> 00:02:58,820 quotes with a the space in between them, 68 00:02:58,820 --> 00:03:02,750 and the three closing right parentheses. Then 69 00:03:02,750 --> 00:03:04,280 we'll just print out at the value of 70 00:03:04,280 --> 00:03:07,820 map underscore words. So if we run the 71 00:03:07,820 --> 00:03:10,040 program again now, you can see there 72 00:03:10,040 --> 00:03:12,950 that we've got the identical output. So map 73 00:03:12,950 --> 00:03:15,320 takes two arguments. The first is a 74 00:03:15,320 --> 00:03:17,870 function and I've used the upper 75 00:03:17,870 --> 00:03:19,870 function from the string class str. 76 00:03:19,870 --> 00:03:22,490 Remember that when passing a function as 77 00:03:22,490 --> 00:03:24,410 an argument, you don't include the 78 00:03:24,410 --> 00:03:26,690 opening and closing parentheses. When you 79 00:03:26,690 --> 00:03:28,580 use parentheses you're passing the 80 00:03:28,580 --> 00:03:31,010 result of calling the function, but here 81 00:03:31,010 --> 00:03:32,570 we want to pass the function itself. 82 00:03:32,570 --> 00:03:35,150 The second argument's an iterator. 83 00:03:35,150 --> 00:03:36,650 You can use anything that can be 84 00:03:36,650 --> 00:03:38,810 iterated over, such as a string or a list. 85 00:03:38,810 --> 00:03:41,300 So map underscore capitals is using the 86 00:03:41,300 --> 00:03:44,210 string text and map iterates over each 87 00:03:44,210 --> 00:03:46,400 character in the string and calls the 88 00:03:46,400 --> 00:03:49,190 str dot upper function for each one. It 89 00:03:49,190 --> 00:03:51,410 then builds up another interable which we 90 00:03:51,410 --> 00:03:53,930 convert to a list. Map underscore words 91 00:03:53,930 --> 00:03:56,030 is doing the same thing but creates an 92 00:03:56,030 --> 00:03:58,220 interable by splitting the text into 93 00:03:58,220 --> 00:04:00,590 words. Split returns the list, remember, 94 00:04:00,590 --> 00:04:03,110 so the split list is an interable that 95 00:04:03,110 --> 00:04:05,060 map's iterating over, and that's 96 00:04:05,060 --> 00:04:07,130 basically what map does. It calls the 97 00:04:07,130 --> 00:04:09,590 function for each item in the interable 98 00:04:09,590 --> 00:04:12,380 and stores the result in a new interable. 99 00:04:12,380 --> 00:04:14,390 So we've used that interable to create a list, 100 00:04:14,390 --> 00:04:16,339 but we could have, instead, just iterated 101 00:04:16,339 --> 00:04:19,579 over it. So as an example there, 102 00:04:19,579 --> 00:04:23,270 we could type for x in map parentheses str 103 00:04:23,270 --> 00:04:28,150 dot upper comma text dot split, 104 00:04:28,150 --> 00:04:31,190 then in left and right parentheses, single 105 00:04:31,190 --> 00:04:33,259 quote and a space between, and the two 106 00:04:33,259 --> 00:04:35,449 closing right parentheses and a colon on 107 00:04:35,449 --> 00:04:37,130 the end there, so we iterate over 108 00:04:37,130 --> 00:04:41,020 each element, and then print and in parentheses, x. 109 00:04:41,020 --> 00:04:44,810 So if you run that, you can see that this 110 00:04:44,810 --> 00:04:47,210 is exactly the same map code, but instead 111 00:04:47,210 --> 00:04:49,639 of converting the interable to a list, we 112 00:04:49,639 --> 00:04:52,430 iterate over it and print each item. 113 00:04:52,430 --> 00:04:53,720 And you can see there that the output was 114 00:04:53,720 --> 00:04:56,750 the capitalized words from text. So is 115 00:04:56,750 --> 00:04:58,430 there anything to be gained from using 116 00:04:58,430 --> 00:05:00,380 map instead of a comprehension? In my 117 00:05:00,380 --> 00:05:02,449 opinion, I'd say there isn't. 118 00:05:02,449 --> 00:05:04,610 The comprehensions are easier to write 119 00:05:04,610 --> 00:05:07,669 and more importantly, easier to read. It's just 120 00:05:07,669 --> 00:05:09,409 more obvious what they're doing, 121 00:05:09,409 --> 00:05:11,720 which was Guido's main reason for wanting to 122 00:05:11,720 --> 00:05:14,990 remove map from Python 3. But what about 123 00:05:14,990 --> 00:05:17,150 performance? Well you now know how to 124 00:05:17,150 --> 00:05:19,639 test that performance yourself. However, 125 00:05:19,639 --> 00:05:21,740 there are ways to make timing functions 126 00:05:21,740 --> 00:05:24,080 even easier, and it may not have been 127 00:05:24,080 --> 00:05:26,210 obvious from the earlier video. It's a 128 00:05:26,210 --> 00:05:27,710 technique I'm going to rely on in the 129 00:05:27,710 --> 00:05:29,569 next few videos, and I'll take the 130 00:05:29,569 --> 00:05:31,699 opportunity to introduce it and explain 131 00:05:31,699 --> 00:05:35,509 it here. So it's now challenge time. 132 00:05:35,509 --> 00:05:37,070 So the challenge is to wrap each of the 133 00:05:37,070 --> 00:05:39,199 four blocks of code in function 134 00:05:39,199 --> 00:05:41,599 definitions then use the timeit module 135 00:05:41,599 --> 00:05:44,719 to time each one. Remember to import timeit 136 00:05:44,719 --> 00:05:47,240 at the start of the file. Now my 137 00:05:47,240 --> 00:05:48,740 solution will use a slightly different 138 00:05:48,740 --> 00:05:51,830 approach, to save time in the video. The 139 00:05:51,830 --> 00:05:53,150 test of whether your solution works, 140 00:05:53,150 --> 00:05:55,460 though, is if it successfully times all 141 00:05:55,460 --> 00:05:57,650 four approaches to capitalizing the 142 00:05:57,650 --> 00:05:59,990 characters and words in text. Alright 143 00:05:59,990 --> 00:06:01,490 so that's the challenge. Pause the video 144 00:06:01,490 --> 00:06:03,229 and see how you go with it, and when 145 00:06:03,229 --> 00:06:04,490 you're ready come back and you can view 146 00:06:04,490 --> 00:06:07,999 my solution. So pause the video now. 147 00:06:07,999 --> 00:06:10,039 Alright, so welcome back. Let's go 148 00:06:10,039 --> 00:06:11,839 through the solution to the challenge, 149 00:06:11,839 --> 00:06:14,779 step by step. So the first step is 150 00:06:14,779 --> 00:06:17,059 to include each code block in a function 151 00:06:17,059 --> 00:06:19,639 definition, so let's do that. So starting 152 00:06:19,639 --> 00:06:21,889 at the top here, on line 3, we're going to 153 00:06:21,889 --> 00:06:23,389 make that a function. I'm going to add a 154 00:06:23,389 --> 00:06:26,829 line, def space comp underscore caps 155 00:06:26,829 --> 00:06:29,019 parentheses colon 156 00:06:29,019 --> 00:06:32,239 and then we'll indent the code, the next 157 00:06:32,239 --> 00:06:34,669 two lines, and we'll change the print to 158 00:06:34,669 --> 00:06:39,860 a return capitals. That's the first one, 159 00:06:39,860 --> 00:06:41,889 and we need to make sure that we're 160 00:06:41,889 --> 00:06:43,939 spacing this out correctly. We need two 161 00:06:43,939 --> 00:06:48,559 lines, like so, to avoid those warnings or 162 00:06:48,559 --> 00:06:50,419 to get rid of those warnings. Next we 163 00:06:50,419 --> 00:06:52,459 want to create the map underscore caps 164 00:06:52,459 --> 00:06:54,739 function, so def space map underscore 165 00:06:54,739 --> 00:06:57,769 caps parentheses colon. We'll indent these 166 00:06:57,769 --> 00:07:00,169 two lines again, converting the second 167 00:07:00,169 --> 00:07:04,459 line, instead of a print to a return, 168 00:07:04,459 --> 00:07:06,409 and remembering to add two spaces or two 169 00:07:06,409 --> 00:07:08,419 lines between the end of the function and 170 00:07:08,419 --> 00:07:10,429 the start of the next one. Next one we're 171 00:07:10,429 --> 00:07:13,489 going to call def comp underscore words 172 00:07:13,489 --> 00:07:16,039 because it's a comprehension version, so 173 00:07:16,039 --> 00:07:17,659 comp underscore words parentheses 174 00:07:17,659 --> 00:07:28,819 colon, indent again and return words. Okay, 175 00:07:28,819 --> 00:07:30,800 and then the fourth one, making sure 176 00:07:30,800 --> 00:07:32,449 we've got two lines there separating it, 177 00:07:32,449 --> 00:07:34,849 and it's going to be def map underscore 178 00:07:34,849 --> 00:07:38,029 words parentheses colon. 179 00:07:38,029 --> 00:07:40,369 We'll indent these two lines, and this time we 180 00:07:40,369 --> 00:07:43,309 want to change the variable name here, to 181 00:07:43,309 --> 00:07:45,469 avoid any problems. I'm going to call 182 00:07:45,469 --> 00:07:48,319 that map underscore x instead, or map 183 00:07:48,319 --> 00:07:50,149 underscore w it should say, for map 184 00:07:50,149 --> 00:07:51,979 underscore words, and then we're going to 185 00:07:51,979 --> 00:07:56,089 return on the next line, map underscore w. 186 00:07:56,089 --> 00:07:59,569 And then ww want a two line space there. 187 00:07:59,569 --> 00:08:01,129 Well actually, what we can do now 188 00:08:01,129 --> 00:08:03,589 is delete that, because you no longer need 189 00:08:03,589 --> 00:08:06,679 that other code. Before attempting to time 190 00:08:06,679 --> 00:08:08,059 the function, we should really call each 191 00:08:08,059 --> 00:08:09,259 one just to make sure that it still 192 00:08:09,259 --> 00:08:11,479 works. So let's do that. So I'm going to add 193 00:08:11,479 --> 00:08:15,169 if on line 26, underscore underscore name 194 00:08:15,169 --> 00:08:19,009 underscore underscore equals equals single quotes 195 00:08:19,009 --> 00:08:20,940 underscore main underscore 196 00:08:20,940 --> 00:08:22,890 underscore so, we've done that a 197 00:08:22,890 --> 00:08:25,860 number of times now, a colon, and let's print them 198 00:08:25,860 --> 00:08:27,840 out. So print comp underscore caps, the first 199 00:08:27,840 --> 00:08:31,170 function, results, second one, print map 200 00:08:31,170 --> 00:08:32,750 underscore caps, 201 00:08:32,750 --> 00:08:35,400 third one print, it's going to be 202 00:08:35,400 --> 00:08:38,820 comp underscore words and the fourth 203 00:08:38,820 --> 00:08:43,820 one, print map underscore words. Okay. 204 00:08:43,820 --> 00:08:45,900 Let's run the program to make sure 205 00:08:45,900 --> 00:08:49,170 it works, and you can see that it's working 206 00:08:49,170 --> 00:08:51,420 nicely. Alright so let's finish the video 207 00:08:51,420 --> 00:08:53,280 here. In the next one, we'll move on 208 00:08:53,280 --> 00:08:55,890 and we'll start timing the call to these 209 00:08:55,890 --> 00:08:57,630 functions. So I'll see you in the next 210 00:08:57,630 --> 00:08:59,870 video.