1 00:00:00,300 --> 00:00:04,830 Welcome to listen 20 which roughly covers pages one hundred twenty eight to one hundred forty one of 2 00:00:04,830 --> 00:00:07,500 the automate the boring stuff with pipe on textbook. 3 00:00:07,500 --> 00:00:13,270 Just as a quick reminder you can actually view the entire book online at automate the boring stuff dotcom 4 00:00:13,430 --> 00:00:14,000 . 5 00:00:14,100 --> 00:00:19,350 So if you don't have a print copy you can just scroll down and then click on whichever chapter that 6 00:00:19,350 --> 00:00:20,160 we're going over. 7 00:00:20,160 --> 00:00:27,390 Inside this class I'm just like listen 15 covered a lot of useful list methods. 8 00:00:27,390 --> 00:00:30,230 This lesson will cover a lot of useful string methods. 9 00:00:30,390 --> 00:00:36,330 Keep in mind that unlike list methods the stream methods return a new string value rather than modify 10 00:00:36,330 --> 00:00:37,470 the string in place. 11 00:00:37,590 --> 00:00:41,620 Since strings are immutable it's impossible to modify them in place anyway. 12 00:00:42,240 --> 00:00:50,490 Let's take a look at the upper and lower string methods like have a variable like spam hello world and 13 00:00:50,520 --> 00:00:58,540 I could call that string values up or method and it returns a uppercase version of that string. 14 00:00:58,590 --> 00:01:02,250 Remember string values are immutable so they can't be modified in place. 15 00:01:02,250 --> 00:01:05,910 Spam still contains that lower case value. 16 00:01:05,910 --> 00:01:11,280 If I actually wanted to modify the variant the value in the variable spam would have to have something 17 00:01:11,280 --> 00:01:14,180 like spam equals spam. 18 00:01:14,220 --> 00:01:14,550 Upper 19 00:01:17,430 --> 00:01:24,060 and the lower method returns a version of that string in all lowercase non-leather characters like the 20 00:01:24,060 --> 00:01:30,180 space or the exclamation mark are completely unaffected by the upper and lower methods. 21 00:01:30,180 --> 00:01:33,810 These methods are helpful if you need to make a case insensitive comparison. 22 00:01:33,810 --> 00:01:38,880 For example if I was making some sort of game program and I printed out you want to play again I expected 23 00:01:38,880 --> 00:01:41,250 a yes or no answer. 24 00:01:41,850 --> 00:01:47,300 You would have some code that calls the input function and the player types in yes or no. 25 00:01:47,880 --> 00:01:54,490 Let's say I type in yes answer stores the lower case yes string. 26 00:01:54,660 --> 00:02:00,120 The player could have easily typed in capital Y E S. 27 00:02:00,360 --> 00:02:00,810 Once 28 00:02:04,140 --> 00:02:11,640 the player could have easily typed in capital Y E S into any code that we have that looks like this 29 00:02:11,640 --> 00:02:11,830 . 30 00:02:11,850 --> 00:02:15,330 If you answer he calls y e s lowercase 31 00:02:23,720 --> 00:02:31,280 it would fail because this expression evaluates to false if answer contains a capital contains an uppercase 32 00:02:31,290 --> 00:02:32,520 version of Yes. 33 00:02:32,550 --> 00:02:38,760 So instead we could have an expression that just automatically converts it to lower case before doing 34 00:02:38,760 --> 00:02:39,790 the comparison. 35 00:02:39,920 --> 00:02:47,370 So now it doesn't matter if answer contains a capital yes or maybe lower case and upper case characters 36 00:02:48,900 --> 00:02:53,460 in code will still work the same and still have something like this. 37 00:02:53,660 --> 00:03:03,330 Books still have something like this and it works with any response string values also have an is upper 38 00:03:03,330 --> 00:03:09,550 and lower method that returns a boolean value depending on if the strings are uppercase or lowercase 39 00:03:09,570 --> 00:03:10,590 . 40 00:03:10,590 --> 00:03:15,420 Let me try again with storing hello world in inside of spam. 41 00:03:15,750 --> 00:03:22,740 I can colspan is lower and this will return false because there is a letter character that's in upper 42 00:03:22,740 --> 00:03:34,440 case so I could change this to be a lowercase letter and now it turns it evaluates to true and I can 43 00:03:34,440 --> 00:03:41,860 do the same thing with his upper altar's first make this only have uppercase characters. 44 00:03:41,950 --> 00:03:47,800 Now spam is upper for return true. 45 00:03:47,850 --> 00:03:49,950 Note that if I just have the blank string 46 00:03:52,630 --> 00:03:55,740 both spam that is upper and is lower 47 00:03:58,560 --> 00:04:05,670 both are false there needs to be at least one uppercase or one lowercase character for is upper and 48 00:04:05,880 --> 00:04:08,740 lower to return TRUE respectively. 49 00:04:08,790 --> 00:04:14,580 So if I just called this loss during value like one two three four five both is lower and is upper would 50 00:04:14,580 --> 00:04:17,960 return false because there's no letters inside the string. 51 00:04:18,080 --> 00:04:23,550 Well since the upper and lower string methods themselves return strings you can call string methods 52 00:04:23,630 --> 00:04:26,280 and those return String values as well. 53 00:04:26,280 --> 00:04:29,710 Expressions that do this will look like a chain of method calls. 54 00:04:30,090 --> 00:04:39,870 So if I have the string hello and I call its upper method it returns the string capital hello and then 55 00:04:39,870 --> 00:04:46,890 on that string I could in turn call something like Is upper which then evaluates to a boolean value 56 00:04:46,890 --> 00:04:46,920 . 57 00:04:46,920 --> 00:04:54,370 So this entire expression evaluates to true B of the string hello and then we call its string method 58 00:04:54,450 --> 00:04:55,410 upper on that. 59 00:04:55,590 --> 00:05:04,230 And this returns a string itself which we call its method is oppor which then returns a boolean value 60 00:05:04,230 --> 00:05:04,370 . 61 00:05:04,380 --> 00:05:10,780 True there are several other of these string methods that begin with the word is. 62 00:05:10,860 --> 00:05:16,950 These methods return a boolean value that describes the nature of the string we have is Alpha that returns 63 00:05:16,950 --> 00:05:20,910 true if the string consists of only letters and it's not blank. 64 00:05:20,940 --> 00:05:26,790 Is Al name which returns true if the string only consists of letters and numbers that is it consists 65 00:05:26,790 --> 00:05:27,000 of. 66 00:05:27,000 --> 00:05:31,870 Alphanumerics is decimal which returns true if there are only numeric characters. 67 00:05:32,010 --> 00:05:37,860 Is space that returns true if there is only space characters and is title that returns true if the string 68 00:05:37,860 --> 00:05:43,240 consist of words that begin with uppercase letters followed by only lower case letters. 69 00:05:43,320 --> 00:05:47,430 So I'll type all of these out into the interactive shell we have. 70 00:05:47,430 --> 00:05:54,270 The string is alpha and this will return true because it only consists of letters. 71 00:05:54,320 --> 00:05:55,590 But if I have something like. 72 00:05:55,720 --> 00:06:02,940 Hello 2:59 is off a wrong turn return false because this one two three means that it's not just alphabetical 73 00:06:02,940 --> 00:06:04,060 characters. 74 00:06:04,920 --> 00:06:11,520 Whereas if I have hello One two three and I call is l salnum which is Fern's true. 75 00:06:11,520 --> 00:06:17,150 If there is only alphanumerics that is letters and numbers only then that returns true. 76 00:06:17,360 --> 00:06:24,990 I have something like 1 to 3 and call is decimal on it and that returns true or if I have just a bunch 77 00:06:24,990 --> 00:06:29,440 of empty space I could call it space. 78 00:06:29,550 --> 00:06:32,190 I would say yes there is nothing but empty space. 79 00:06:32,210 --> 00:06:34,560 Whitespace characters inside the string. 80 00:06:34,750 --> 00:06:39,160 Although see I had something like hello world and cold space on that. 81 00:06:39,210 --> 00:06:43,660 That would return false because these are not space characters. 82 00:06:43,680 --> 00:06:47,610 However if I had a if I had an expression. 83 00:06:47,610 --> 00:06:51,030 Sort of like where is that space. 84 00:06:51,070 --> 00:06:54,020 0 1 2 3 4 5. 85 00:06:54,190 --> 00:07:02,910 I could call it space on that and that would return true because this index returns that single space 86 00:07:03,060 --> 00:07:10,810 from the middle in between Hello world and then is title is kind of crazy looking. 87 00:07:11,040 --> 00:07:20,550 It will turn true only if all of the words inside that string begin with a uppercase character and have 88 00:07:20,550 --> 00:07:25,950 nothing but lowercase characters in them. 89 00:07:27,370 --> 00:07:32,230 There is also a corresponding title string method. 90 00:07:33,600 --> 00:07:35,620 Just like there is lower and upper. 91 00:07:36,060 --> 00:07:38,180 So that's a lot of different string methods. 92 00:07:38,280 --> 00:07:40,100 You don't have to memorize all of them. 93 00:07:40,140 --> 00:07:44,660 Just remember that they exist and you can google for them later. 94 00:07:44,730 --> 00:07:50,820 Next the starts with an ends with methods return true if a string value that they're called on begins 95 00:07:50,820 --> 00:07:54,330 or ends respectively with the string that's passed to the method. 96 00:07:54,570 --> 00:08:01,560 So if we had a string like hello world we could call starts with and then passed that string. 97 00:08:01,590 --> 00:08:05,750 Hello and this will return true. 98 00:08:06,000 --> 00:08:09,670 We could even make that much simpler and say does it start with the letter H. 99 00:08:09,690 --> 00:08:11,090 And that's true. 100 00:08:12,180 --> 00:08:18,860 Whereas this would return false because it does not start with L-O. 101 00:08:18,930 --> 00:08:21,220 We need that beginning H right here. 102 00:08:21,480 --> 00:08:26,660 Similarly we have an ends with method. 103 00:08:27,590 --> 00:08:33,270 Note that it starts with an S at the end and ends with an S at the end. 104 00:08:33,750 --> 00:08:37,650 So we could ask it O does it end with world exclamation point. 105 00:08:37,770 --> 00:08:39,570 And this would return true. 106 00:08:39,600 --> 00:08:41,330 Of course if we. 107 00:08:41,700 --> 00:08:49,830 Although if we didn't have that exclamation mark at the end this would return false. 108 00:08:49,980 --> 00:08:54,960 The join method is useful when you have a list of strings that need to be joined together into a single 109 00:08:54,960 --> 00:08:56,180 string value. 110 00:08:56,280 --> 00:09:01,820 The join method is called on a string gets past a list of strings and returns a string. 111 00:09:02,550 --> 00:09:03,930 So here's a common example. 112 00:09:03,930 --> 00:09:11,470 We have the string comma and we'll use that to join together a list of strings. 113 00:09:11,810 --> 00:09:17,590 Let's say cats rats bats. 114 00:09:18,210 --> 00:09:24,810 So this method call returns a string that has each of these individual strings in this list combined 115 00:09:24,810 --> 00:09:27,720 together and joined with this string. 116 00:09:27,780 --> 00:09:30,700 So a combo appears in between each of them. 117 00:09:31,160 --> 00:09:35,550 We could change this so that we have nothing that joins them just have the blank string so that they 118 00:09:35,550 --> 00:09:37,920 all just get crammed together already. 119 00:09:37,950 --> 00:09:44,630 Or perhaps we could have a single space in them so that there is a single space there. 120 00:09:45,110 --> 00:09:52,770 Or even say to newline characters have Slash selection so that way when we passed this twig print function 121 00:09:52,770 --> 00:10:00,660 call it will print it out with a new line here and then another new line here to have a gap in between 122 00:10:00,690 --> 00:10:02,930 each of the words. 123 00:10:03,030 --> 00:10:05,250 The split method does the opposite. 124 00:10:05,250 --> 00:10:10,930 It's cold on a string value and returns a list of strings that have the string. 125 00:10:10,950 --> 00:10:19,890 My name is Simon and when I call split on it it returns a list and inside this list or all the individual 126 00:10:19,890 --> 00:10:27,890 words from inside that string it splits it on whitespace characters it we can have it split on other 127 00:10:27,890 --> 00:10:34,310 characters as well just by passing a different value to the split method say I wanted it to split on 128 00:10:34,490 --> 00:10:37,400 the letter M instead of on spaces. 129 00:10:37,400 --> 00:10:43,850 Now this list will have my number as the first string and then it splits. 130 00:10:43,850 --> 00:10:51,950 It cuts out this M set everything up to the next AM is in the second string and then the rest of that 131 00:10:51,950 --> 00:10:53,390 is the third string. 132 00:10:53,440 --> 00:11:00,980 This is just like how it used to go up to the first space character and then have the next string be 133 00:11:01,070 --> 00:11:02,840 up to the next space character. 134 00:11:03,320 --> 00:11:06,500 So you can split on anything that you want. 135 00:11:06,500 --> 00:11:12,440 The are just an L just string methods or turny padded version of a string that they're called on with 136 00:11:12,440 --> 00:11:17,000 spaces inserted to left justify or right justify the text. 137 00:11:17,000 --> 00:11:21,670 So the first argument to both methods is the integer length for the justified string. 138 00:11:21,920 --> 00:11:25,510 So if I have the string Hello I can write justify it. 139 00:11:25,940 --> 00:11:29,150 Let's say I want the total length of the return String to be 10. 140 00:11:29,150 --> 00:11:35,390 So in this case Python inserts as many space characters as needed to make the total length of this string 141 00:11:37,460 --> 00:11:39,360 to be 10. 142 00:11:40,010 --> 00:11:44,780 And I can do the same thing with the L just method to less left justified. 143 00:11:44,780 --> 00:11:47,360 This will add white space padding to the hand 144 00:11:50,300 --> 00:11:56,960 and I can try passing a different value to justify it with 20 spaces and an optional second argument 145 00:11:56,960 --> 00:12:03,050 can be passed you are just an L just to specify a difference Fille character other than a space. 146 00:12:03,200 --> 00:12:09,490 So if I had hello that are just and I wanted it to be 20 characters long. 147 00:12:09,500 --> 00:12:17,000 And then also have asterisks instead of spaces I could create a string easily with stars at the front 148 00:12:17,000 --> 00:12:27,020 of it or say I wanted the text Hello to the left justified with 25 characters and then dashes instead 149 00:12:27,020 --> 00:12:27,890 . 150 00:12:27,890 --> 00:12:33,710 And there's also a center method that works just like l just in are just what centrists the text rather 151 00:12:33,710 --> 00:12:36,780 than justifying it to the left or right. 152 00:12:37,270 --> 00:12:38,040 Second half. 153 00:12:38,390 --> 00:12:39,290 Hello. 154 00:12:39,440 --> 00:12:45,970 And then centered so that the entire string is 20 characters long with the text in the center. 155 00:12:45,980 --> 00:12:51,530 Or I could have maybe equal sign as the fill character instead. 156 00:12:51,530 --> 00:12:59,770 This is kind of nice because you could have a variable that contains something like name equals Al. 157 00:13:02,940 --> 00:13:11,060 Or it could change that to be a very long name like Wendell the law of the law. 158 00:13:11,720 --> 00:13:17,030 And that same code will put that name in the center with as many equal signs on either side as necessary 159 00:13:17,030 --> 00:13:18,260 . 160 00:13:18,310 --> 00:13:20,000 It uses the same code 161 00:13:23,630 --> 00:13:29,150 sometimes you might want to strip off whitespace characters like spaces or tabs or new lines from the 162 00:13:29,150 --> 00:13:32,900 left side or the right side or both sides of the string going back. 163 00:13:32,900 --> 00:13:40,160 If we had this hello that are just we had too much space on the on the left side of this when we want 164 00:13:40,160 --> 00:13:47,480 to get rid of that we can call the strip string method to remove that. 165 00:13:47,540 --> 00:13:58,590 So let's say I have that in spam and I could call strip on that string to remove that whitespace. 166 00:13:58,670 --> 00:14:01,330 This doesn't modify spam in place. 167 00:14:01,610 --> 00:14:03,250 Spam still has all of that in there. 168 00:14:03,260 --> 00:14:05,690 This just returns a brand new string. 169 00:14:05,990 --> 00:14:12,980 So if I wanted to change it I would have spam equals spam got strip No remove whitespace from either 170 00:14:12,980 --> 00:14:13,520 side 171 00:14:17,240 --> 00:14:19,050 of the string. 172 00:14:20,620 --> 00:14:24,620 Let's say we only want to move remove the whitespace from the left side of the string we could call 173 00:14:24,650 --> 00:14:32,150 L strip or we could call our strip turr just remove whitespace from the right side of the string. 174 00:14:32,150 --> 00:14:38,000 We could also pass the strip methods a string with characters that we want to remove instead of whitespace 175 00:14:38,000 --> 00:14:41,600 . 176 00:14:41,870 --> 00:14:51,610 So if I had a variable like spam spam Bacons spam eggs spam spam I could Colstrip on that and pass it 177 00:14:51,600 --> 00:14:51,650 . 178 00:14:51,680 --> 00:14:54,880 The letters KMP capital S.. 179 00:14:54,950 --> 00:15:01,970 I can have this in any order I'm just specifying letters not an actual word and this or move all the 180 00:15:01,970 --> 00:15:09,360 capital S is PS A's and M's from either side of the string and return that new string guy. 181 00:15:09,440 --> 00:15:11,680 There is however still spam in the middle. 182 00:15:11,840 --> 00:15:17,600 That's just because it removed those letters up to the first character that wasn't passed to strict 183 00:15:17,600 --> 00:15:18,410 method. 184 00:15:18,890 --> 00:15:22,600 And then the same on the inside it just went down to here. 185 00:15:22,700 --> 00:15:30,560 So this is the string that was returned in the replace string method takes two arguments a string to 186 00:15:30,560 --> 00:15:33,860 look for and a string to replace it with. 187 00:15:33,890 --> 00:15:42,140 So if I had a string like hello they're stored in spam I could code replace and replace every e with 188 00:15:42,500 --> 00:15:43,430 x y z 189 00:15:47,430 --> 00:15:50,260 and that's all the string methods that will cover in this lesson. 190 00:15:50,270 --> 00:15:51,770 Let's go over one more thing. 191 00:15:51,770 --> 00:15:58,370 The paperclip module has copy and paste functions that can send text to and receive text from your computer's 192 00:15:58,370 --> 00:16:03,260 clipboard so sending the output of your program to the clipboard will make it really easy to paste it 193 00:16:03,260 --> 00:16:07,730 to an email or to a word processor software or some other program. 194 00:16:08,210 --> 00:16:11,480 The paperclip doesn't come with Python to install it. 195 00:16:11,480 --> 00:16:16,500 Follow the directions for installing third party modules with the pip tool in Appendix A. 196 00:16:16,970 --> 00:16:19,690 I can show you very quickly how to do it on Windows. 197 00:16:19,700 --> 00:16:25,100 I'm just going to hit window key R and run CM D. 198 00:16:26,620 --> 00:16:28,790 I'll just go to the directory. 199 00:16:29,180 --> 00:16:37,400 So change directory to where Python is installed and go to its scripts folder that has this program 200 00:16:37,560 --> 00:16:38,800 pip dot exe. 201 00:16:39,160 --> 00:16:45,410 and I'll just type pip dot exe install paperclip and this will automatically download and install it 202 00:16:45,470 --> 00:16:46,820 onto your system. 203 00:16:46,880 --> 00:16:48,360 In this case I've already have it. 204 00:16:48,380 --> 00:16:52,890 I already have it installed so it says you don't need to install it again. 205 00:16:54,110 --> 00:16:57,230 So after installing it you can check to see if the install worked. 206 00:16:57,260 --> 00:16:59,260 Just trying to import paperclip. 207 00:16:59,260 --> 00:17:06,320 And if nothing shows up then that means it's successfully been installed and paperclip has a copy and 208 00:17:06,560 --> 00:17:11,110 paste functions that can copy text to the clipboard. 209 00:17:11,120 --> 00:17:21,050 So say I can copy this string hello with lots of exclamation marks and now when I try to paste text 210 00:17:22,850 --> 00:17:26,430 I can see that this text was indeed copied to the clipboard. 211 00:17:26,610 --> 00:17:28,970 Or I can call paperclips. 212 00:17:29,120 --> 00:17:33,320 Paste function and that will return the text that's already on the clipboard. 213 00:17:33,380 --> 00:17:40,190 So if I wanted to get that as a string value I can just call paperclips up paste to recap. 214 00:17:40,190 --> 00:17:48,540 Upper and lower return in uppercase or lowercase version of the string is upper is lower is alpha. 215 00:17:48,560 --> 00:17:52,360 Is Al knowm is decimal is space is title. 216 00:17:52,640 --> 00:17:58,310 All of those is string for methods return true or false depending on if the string is that respective 217 00:17:58,310 --> 00:18:01,610 kind of string starts with and ends with. 218 00:18:01,610 --> 00:18:03,280 Also return balls. 219 00:18:03,680 --> 00:18:08,760 The join method will return a string that combines the strings from a list. 220 00:18:08,870 --> 00:18:15,800 The split method will return a list of strings are just eldest and center will return a string that's 221 00:18:15,800 --> 00:18:22,280 padded with spaces or some other character that you specify the strip are strip and L strip methods 222 00:18:22,280 --> 00:18:25,880 will return a string with the whitespace stripped off from the sides. 223 00:18:25,880 --> 00:18:30,800 Replace will replace all occurrences of the first string argument with the second string argument that 224 00:18:30,800 --> 00:18:36,860 you pass it and the paperclip module has copy and paste functions so that your programs can use the 225 00:18:36,860 --> 00:18:38,730 computer's clipboard.