1 00:00:05,200 --> 00:00:09,520 In the previous video, we saw how to access files in the current directory. 2 00:00:09,520 --> 00:00:13,861 Your first question is probably, "How do I know what is the current directory?". 3 00:00:13,861 --> 00:00:18,814 Your operating system tries to help there. Have a look at your operating system's prompt. 4 00:00:18,814 --> 00:00:22,876 That's the text that appears, just before where you type your commands. 5 00:00:22,960 --> 00:00:27,040 On Windows, the prompt ends with a greater-than symbol. Everything before 6 00:00:27,040 --> 00:00:33,120 that is the full path to the current directory. So my current directory is called Functions_Intro. 7 00:00:33,120 --> 00:00:37,330 That's inside a directory called current-python-masterclass-remaster. 8 00:00:37,330 --> 00:00:41,360 The current-python-masterclass-remaster directory is in the root of drive Y. 9 00:00:41,360 --> 00:00:45,680 On your Windows computers, you should see the complete path in your prompt. 10 00:00:45,680 --> 00:00:50,400 Note though, that the prompt can be changed. If you're using a company computer, 11 00:00:50,400 --> 00:00:54,480 the prompt might be different. Please don't ask how to change it. 12 00:00:54,480 --> 00:00:58,160 A bit of googling will get you there, but if your company has changed the prompt, 13 00:00:58,160 --> 00:01:00,800 then you may not be able to change it back. 14 00:01:00,800 --> 00:01:03,600 So you can use the prompt to keep track of where you are. 15 00:01:03,600 --> 00:01:08,327 On a Mac or Linux, the terminal prompt only shows the name of the current directory. 16 00:01:08,400 --> 00:01:12,080 You don't get to see the full path. It also abbreviates the name of your 17 00:01:12,080 --> 00:01:16,762 home folder to ~, a tilde character. If you lose track of where you are, 18 00:01:16,762 --> 00:01:21,992 or just want to check, you can use the PWD command – short for Print Working Directory: 19 00:01:24,320 --> 00:01:28,514 That's a useful command, to check the full path to the directory you're in. 20 00:01:28,640 --> 00:01:32,400 On Windows, if you need to check, you can use the cd command, 21 00:01:32,400 --> 00:01:35,239 without giving it a directory to change into: 22 00:01:37,120 --> 00:01:41,120 That produces the same output as the terminal's PWD command. 23 00:01:41,120 --> 00:01:44,720 Well, almost the same. There is a slight difference, 24 00:01:44,720 --> 00:01:50,000 and this is the second difference between paths on Windows and paths on Linux or Mac. 25 00:01:50,800 --> 00:01:55,840 Windows paths use the backslash character, to separate the various parts of the path. 26 00:01:55,840 --> 00:02:01,520 We start with a drive letter, followed by a colon. That's optional, and if a path doesn't contain a 27 00:02:01,520 --> 00:02:06,480 drive letter (followed by a colon) then it refers to something on the current drive. 28 00:02:06,480 --> 00:02:10,639 After the drive letter, if there is one, we have a \. 29 00:02:10,639 --> 00:02:16,898 Each of the directories, in the path, are separated from the previous one with a backslash. 30 00:02:18,480 --> 00:02:22,640 The path above represents a file called course_notes.txt. 31 00:02:22,640 --> 00:02:27,360 The file is in a folder called Documents, which is in a folder called timbuchalka. 32 00:02:27,360 --> 00:02:33,835 The timbuchalka folder is inside a folder called Users, which is in the root folder on Drive C. 33 00:02:35,360 --> 00:02:38,960 On Linux or Mac OS, the slash character is used. 34 00:02:38,960 --> 00:02:41,920 This is what the path might look like on a Mac computer. 35 00:02:41,920 --> 00:02:45,040 It will be very similar on a Linux machine; the main difference is 36 00:02:45,040 --> 00:02:49,840 that users' home folders are usually in a directory called home, rather than Users. 37 00:02:52,080 --> 00:02:56,240 The path above represents a file called course_notes.txt. 38 00:02:56,240 --> 00:03:00,960 The file is in a folder called Documents, which is in a folder called timbuchalka. 39 00:03:00,960 --> 00:03:06,630 The timbuchalka folder is inside a folder called Users, which is in the root folder. 40 00:03:08,240 --> 00:03:11,280 I've used the term root folder in both of the last two slides, 41 00:03:11,280 --> 00:03:16,720 so I should explain what the root directory is. The root directory (or folder) is the top 42 00:03:16,720 --> 00:03:21,680 level directory on a drive (in Windows). Each drive has its own root directory, 43 00:03:21,680 --> 00:03:25,945 which is represented by the \ character. So on a Windows computer, 44 00:03:25,945 --> 00:03:30,640 you might have C:\ and Y:\ These represent the top level 45 00:03:30,640 --> 00:03:36,640 directory on drive C and drive Y, respectively. Linux and Mac don't use drive letters. 46 00:03:36,640 --> 00:03:40,000 That means there's only one root directory for the whole file system. 47 00:03:40,000 --> 00:03:44,926 On those operating systems, the root directory is represented by a slash /. 48 00:03:47,040 --> 00:03:52,594 I'll demonstrate using the root directory shortly. First, there's one more thing you need to know about – 49 00:03:52,594 --> 00:03:56,160 absolute and relative paths. An absolute path will get you to your 50 00:03:56,160 --> 00:04:00,640 destination, no matter where you start from. A relative path will get you there from where 51 00:04:00,640 --> 00:04:05,895 you are now. If you use it from somewhere else, you won't get where you want to be. 52 00:04:07,760 --> 00:04:13,360 We use relative paths often, in everyday life. You might be trying to find a particular shop, 53 00:04:13,360 --> 00:04:18,640 in a strange city. You ask for directions, and might be told something like: 54 00:04:18,640 --> 00:04:23,040 "Take the next left, turn right at the church, and it's straight in front of you". 55 00:04:23,040 --> 00:04:27,520 Those directions will only work from where you are. The path from your current location, 56 00:04:27,520 --> 00:04:31,803 to the shop, is relative to your current location. 57 00:04:33,280 --> 00:04:38,240 If I was already in my home directory, and wanted to find that course_notes.txt file, 58 00:04:38,240 --> 00:04:43,680 I can use the relative path: Documents\course_notes.txt 59 00:04:43,680 --> 00:04:49,095 or Documents/course_notes.txt, in a terminal. 60 00:04:50,400 --> 00:04:54,880 When working with relative paths, there are two useful shortcuts you can use. 61 00:04:54,880 --> 00:05:00,400 A dot, or period, refers to the current directory. That's not something that Windows users will need 62 00:05:00,400 --> 00:05:06,640 very often, but it can be useful on Linux or Mac. On those operating systems, you use dot slash, 63 00:05:06,640 --> 00:05:10,560 to tell the operating system to execute a file in the current directory. 64 00:05:10,560 --> 00:05:14,960 That's all I'm going to say about dot. dot dot – two periods – refers 65 00:05:14,960 --> 00:05:21,208 to the directory above the current one. We'll see an example of that, after these slides. 66 00:05:22,960 --> 00:05:27,680 An absolute path specifies the location of a resource regardless of where you start from. 67 00:05:27,680 --> 00:05:33,360 The most common use of absolute paths, in everyday life, is probably internet URLs. 68 00:05:33,360 --> 00:05:38,240 We have to provide the name of the server we want to connect to – for example python.org. 69 00:05:38,240 --> 00:05:42,560 We then provide the name of a page – possibly with some directories before it. 70 00:05:42,560 --> 00:05:45,137 For example, and I'll switch to my browser, 71 00:05:45,468 --> 00:05:47,167 I can type 72 00:05:50,400 --> 00:05:54,867 into the address bar, and we'll get to the page for downloading Python. 73 00:05:56,720 --> 00:06:00,640 Note that the internet is Unix based. So we use slashes, 74 00:06:00,640 --> 00:06:04,800 not backslashes, in the paths. Wherever we are in the world, 75 00:06:04,800 --> 00:06:10,455 that path provides the absolute location of that page, on the python.org server. 76 00:06:11,280 --> 00:06:16,136 The original examples I used, in these slides, were absolute paths. 77 00:06:16,136 --> 00:06:19,040 The path below will find the course notes file, 78 00:06:19,040 --> 00:06:23,198 no matter which drive I'm on, or which directory I happen to be in. 79 00:06:24,400 --> 00:06:28,560 Ok, let's see some examples of using absolute and relative paths. 80 00:06:28,560 --> 00:06:32,800 I'm on Drive Y, in the folder for the Functions_Intro project. 81 00:06:32,800 --> 00:06:37,040 I can check which other project directories I have, by providing the full path to my course 82 00:06:37,040 --> 00:06:40,416 remaster directory. That would be 83 00:06:47,440 --> 00:06:51,120 That uses the absolute path, and it's a lot of typing. 84 00:06:51,120 --> 00:06:54,800 Because I'm already on Drive Y, I can shorten that slightly. 85 00:06:54,800 --> 00:06:58,136 There's no need to specify the drive letter of the drive you're on: 86 00:07:04,960 --> 00:07:09,680 We get the same results. This time, the path is relative. 87 00:07:09,680 --> 00:07:14,400 It doesn't specify the drive letter, so it only works from a location on Drive Y. 88 00:07:14,400 --> 00:07:20,425 In a terminal, the path would be absolute. Linux and Mac operating systems don't use drive letters, 89 00:07:20,425 --> 00:07:25,514 so the slash at the start of the path would mean an absolute path, from the root directory. 90 00:07:25,514 --> 00:07:28,160 What if I wanted to check what was in my home folder? 91 00:07:28,160 --> 00:07:31,611 I'm on Drive Y, so I have to provide the drive letter: 92 00:07:36,960 --> 00:07:41,680 Once again, that's an absolute path. But if you remember, I was in my home 93 00:07:41,680 --> 00:07:45,663 directory before I switched to drive Y. The system knows that, 94 00:07:45,663 --> 00:07:48,957 so I only need to provide the drive letter (with a colon): 95 00:07:52,347 --> 00:07:57,439 Once again, we get the same listing – all the files and directories in my home folder. 96 00:07:57,439 --> 00:08:03,489 Note that I didn't use a backslash there. If I had, we'd get a directory of the root of the C drive: 97 00:08:08,240 --> 00:08:12,800 Alright, I'm going to stop using drive letters now. We'll pretend that I only have one drive on 98 00:08:12,800 --> 00:08:17,680 this computer, and work just with Drive Y. For Linux and Mac users, everything we've 99 00:08:17,680 --> 00:08:22,640 covered so far, with the exception of drive letters, also applies in a terminal. 100 00:08:22,640 --> 00:08:25,656 Let's check what files are in my HelloWorld folder. 101 00:08:25,656 --> 00:08:28,351 I can use an absolute path: 102 00:08:37,001 --> 00:08:41,945 Remember that's not really absolute, on Windows, unless you only have a single drive. 103 00:08:41,945 --> 00:08:44,819 Once again, that's a lot to type. 104 00:08:44,819 --> 00:08:50,720 I can use a relative path, from my current folder. To do that, we need to go back one level, 105 00:08:50,720 --> 00:08:56,216 then go forwards to the HelloWorld directory. We can use .. (dot dot) to do that: 106 00:09:01,120 --> 00:09:07,539 The same thing works in a terminal. I just have to remember to use a slash, rather than a backslash: 107 00:09:12,720 --> 00:09:17,200 Dot dot is very useful, when you want to go back one level from your current directory. 108 00:09:17,200 --> 00:09:22,189 You can chain dot dot, if you want to go back more than one level. For example: 109 00:09:27,200 --> 00:09:31,009 Or, if you're using a Windows command prompt rather than a terminal: 110 00:09:34,880 --> 00:09:39,520 will produce a directory listing of the root. You probably won't use that very often – going 111 00:09:39,520 --> 00:09:44,320 back one level is usually all you want to do. Alright, I'll finish this brief discussion about 112 00:09:44,320 --> 00:09:49,112 file paths with a third difference between Windows, and Mac or Linux. 113 00:09:50,160 --> 00:09:55,676 The title of this slide says it all. On Windows, filenames aren't case sensitive. 114 00:09:55,676 --> 00:09:58,960 HelloWorld.py refers to the same file as helloworld.py 115 00:09:58,960 --> 00:10:06,160 (or any mix of case, eg. hElLowoRlD.PY). On Linux, file names are always case-sensitive. 116 00:10:06,160 --> 00:10:09,840 The 3 names I've just used would refer to 3 separate files. 117 00:10:09,840 --> 00:10:13,120 That's a common source of problems, especially for people moving from 118 00:10:13,120 --> 00:10:20,960 Windows to one of the other operating systems. On Mac OS, by default, file names are not 119 00:10:20,960 --> 00:10:26,640 case-sensitive. But they are case-preserving. You can't create those 3 files in the same 120 00:10:26,640 --> 00:10:31,360 directory, because the names would clash. If you attempted to, you'd end up with 121 00:10:31,360 --> 00:10:35,920 just the contents of the last one – but preserving the case of the first filename. 122 00:10:35,920 --> 00:10:41,280 That can be very confusing! As a guide, treat all filenames as case-sensitive. 123 00:10:41,280 --> 00:10:43,920 Your code will then work on all three operating systems, 124 00:10:43,920 --> 00:10:48,240 and you won't wonder why you can't find a file that you're sure exists. 125 00:10:50,000 --> 00:10:53,680 These few videos have been a quick introduction to file paths. 126 00:10:53,680 --> 00:10:56,580 Experiment with the directories on your own computer. 127 00:10:56,580 --> 00:10:59,680 You may want to browse some files in your operating system's file manager, 128 00:10:59,680 --> 00:11:04,093 then try to do the same thing from the command prompt, or terminal. 129 00:11:05,840 --> 00:11:09,200 If all this is new to you, you'll want to learn more about your filesystem, 130 00:11:09,200 --> 00:11:12,160 and using the command line. Here are some suggestions 131 00:11:12,160 --> 00:11:17,920 for things to google, to find out more: File names and paths on 132 00:11:17,920 --> 00:11:22,400 Using the Windows command prompt Using the terminal 133 00:11:22,400 --> 00:11:25,260 Command line completion 134 00:11:26,800 --> 00:11:29,920 Getting comfortable with file paths, and the command line, 135 00:11:29,920 --> 00:11:34,960 will make your life as a programmer much easier. It's especially important when working with files, 136 00:11:34,960 --> 00:11:38,428 which is what we'll be doing for the rest of this section. 137 00:11:39,120 --> 00:11:41,840 I'll see you in the next video.