1 00:00:05,550 --> 00:00:11,340 To finish off this section of the course I want to discuss these two ideas of name and then the string 2 00:00:11,410 --> 00:00:17,780 main so often confusing part of Python is when you start looking at larger dot pie scripts that you 3 00:00:17,780 --> 00:00:22,610 haven't written yourself you often see at the very bottom this mysterious line of code that says if 4 00:00:22,980 --> 00:00:28,610 underscore underscore name underscore underscore is equal to the string underscore underscore main underscore 5 00:00:28,610 --> 00:00:32,340 underscore colon and then there's a block of code to be executed. 6 00:00:33,550 --> 00:00:38,890 So sometimes the whole idea behind that line of code is that we're importing from a module. 7 00:00:39,010 --> 00:00:44,440 You would actually like to know whether a modules function is being used as an import or if you're using 8 00:00:44,440 --> 00:00:46,880 the original but py file of that module. 9 00:00:48,020 --> 00:00:50,750 So we're work to do is explore all of this a little bit more. 10 00:00:50,960 --> 00:00:55,280 But make sure to check the full explanatory text file that has a written explanation of everything we're 11 00:00:55,280 --> 00:00:56,410 going to cover here. 12 00:00:56,660 --> 00:01:01,340 Well we're going to do basically is just create two simpled up postscripts and try to show you the idea 13 00:01:01,370 --> 00:01:02,280 behind that. 14 00:01:02,360 --> 00:01:08,430 If name is equal to main block of code that is usually at the end a larger dot PI script files. 15 00:01:08,450 --> 00:01:09,330 Let's get started. 16 00:01:10,370 --> 00:01:15,390 OK let's begin by actually creating two new files will create them at my desktop. 17 00:01:15,470 --> 00:01:21,040 I will say for this first file save as and I'm going to say this as one dot pi. 18 00:01:21,260 --> 00:01:24,240 So this one is one of pi. 19 00:01:24,350 --> 00:01:32,750 Then I'll create a new file and I'm going to save this one as to that pi to that PI again at my desk 20 00:01:33,090 --> 00:01:35,180 will level this one to that pi. 21 00:01:35,500 --> 00:01:37,790 So make sure you have those saved. 22 00:01:38,440 --> 00:01:43,510 So let's think about what actually happens when you call a Python script at your command line. 23 00:01:43,570 --> 00:01:47,960 You go to your command line you type python space the name your script the PI. 24 00:01:47,980 --> 00:01:54,940 So what's actually happening when you call Python my script that pi all the code that's the indentation 25 00:01:54,940 --> 00:01:59,860 level 0 essentially something like this is going to get run. 26 00:01:59,860 --> 00:02:03,870 So that means any code that takes the level 0 is going to get run. 27 00:02:03,910 --> 00:02:09,250 And that would mean that your functions which are automatically usually going to be defined in the notation 28 00:02:09,250 --> 00:02:11,010 a little 0 in your classes. 29 00:02:11,020 --> 00:02:14,670 Also the indentation level 0 are all going to be defined. 30 00:02:14,710 --> 00:02:21,040 So unlike other languages in Python there's no main function that you call somewhere at the top of your 31 00:02:21,040 --> 00:02:23,530 script that gets run automatically. 32 00:02:23,530 --> 00:02:29,500 Instead what happens is just implicitly all the code at the indentation level 0 gets run when you call 33 00:02:29,500 --> 00:02:34,180 the script file and you probably have an intuition of that by now since we've been working through that 34 00:02:34,180 --> 00:02:35,020 strategy. 35 00:02:35,020 --> 00:02:43,720 The entire first half of the Course now in Python there is actually a built in variable called name. 36 00:02:43,720 --> 00:02:48,520 So just like there's built in functions this is a built in variable and it's quite obvious that it's 37 00:02:48,520 --> 00:02:53,010 built in because we have two sets of double underscores in the beginning and in the back of it. 38 00:02:53,020 --> 00:02:57,600 So that would allow you to have to really try to overwrite it by accident. 39 00:02:57,610 --> 00:03:04,690 So what happens is this variable name gets assigned a string the pending on how you're running the actual 40 00:03:04,690 --> 00:03:05,460 script. 41 00:03:05,590 --> 00:03:08,170 And if you run the script directly. 42 00:03:08,170 --> 00:03:14,800 So if I went to the command line and I wrote out Python space one that PI with Python is going to do 43 00:03:14,800 --> 00:03:20,110 it's going to assign this builtin variable called name to be equal to 44 00:03:22,820 --> 00:03:24,310 underscore underscore mean. 45 00:03:24,320 --> 00:03:26,310 So Python does this in the background. 46 00:03:26,480 --> 00:03:28,280 Well it really does this. 47 00:03:28,280 --> 00:03:31,100 It assigns the string to the name variable. 48 00:03:31,130 --> 00:03:37,280 When you run it directly and that allows you to have an IF block to check if they're equal to each other 49 00:03:37,910 --> 00:03:39,530 so often will you do something like this. 50 00:03:39,530 --> 00:03:46,880 You say if name is equal to Main and then you can do something because you know that this particular 51 00:03:47,010 --> 00:03:49,520 pipe file is being run directly. 52 00:03:49,760 --> 00:03:53,930 And if you ever run something directly of Python you know this case happens to be true. 53 00:03:54,230 --> 00:03:59,420 So happens is often people just at the very bottom of their code they'll say if name is equal to Main 54 00:03:59,600 --> 00:04:03,690 and then they say kind of run a bunch of functions that they defined here. 55 00:04:03,740 --> 00:04:09,980 So at top they do a bunch of function definitions so function of one function and two so on and so on. 56 00:04:09,980 --> 00:04:13,820 So you can imagine hundreds of lines of function definitions or classes and then all the way at the 57 00:04:13,820 --> 00:04:19,040 bottom they're actually organized or code on what they actually want to execute and they know that they 58 00:04:19,040 --> 00:04:23,750 want to execute it because they say if this built in variable called name happens to be equal to the 59 00:04:23,750 --> 00:04:28,320 string main then I know I'm running this py file directly. 60 00:04:28,640 --> 00:04:33,680 So we're going to explore this whole idea a little further and to do that we're going to do the following 61 00:04:34,100 --> 00:04:35,550 in one pie. 62 00:04:35,570 --> 00:04:37,410 So let's go back here. 63 00:04:37,490 --> 00:04:38,650 This is one that pi. 64 00:04:38,780 --> 00:04:40,150 I will write out the following code. 65 00:04:40,160 --> 00:04:45,890 I will say DPF create a function and this function is going to be very simple. 66 00:04:45,890 --> 00:04:50,780 It will say func in one PI. 67 00:04:50,840 --> 00:04:57,020 So when you call that function it says func in one that pi just printed that out and then I'm also going 68 00:04:57,020 --> 00:05:00,530 to do here is at an indentation level of 0. 69 00:05:00,530 --> 00:05:09,250 So outside of this function I will say top level in one dot pi. 70 00:05:09,290 --> 00:05:14,790 So now I have a function definition as well as a global print statement top level and one that pi. 71 00:05:14,810 --> 00:05:19,400 Then at the bottom of this I will say if you'll notice that's a blind text that will actually autocomplete 72 00:05:19,400 --> 00:05:22,890 this for you if name is equal to mean. 73 00:05:23,030 --> 00:05:24,430 I'm going to delete this. 74 00:05:24,590 --> 00:05:26,450 So I have an IF block of code here. 75 00:05:27,590 --> 00:05:31,410 So if name is equal to made that I know I'm running this directly. 76 00:05:31,430 --> 00:05:42,150 So I will say one that pi is being run directly and then I'm actually going to lineup in ELSE block 77 00:05:42,150 --> 00:05:43,440 with this if statement. 78 00:05:43,500 --> 00:05:47,060 You don't see this that often usually you see if and then you execute your code. 79 00:05:47,190 --> 00:05:51,890 But just to make it clear how this variable is working will also add in an else there will say. 80 00:05:51,960 --> 00:05:52,840 Else. 81 00:05:52,980 --> 00:06:00,140 Prince one PI has been imported. 82 00:06:00,260 --> 00:06:01,390 So I'm going to save that. 83 00:06:01,520 --> 00:06:03,350 And let's take a look at what happens. 84 00:06:03,350 --> 00:06:04,940 I defined this function. 85 00:06:05,000 --> 00:06:10,790 I print out this statement whenever you call 1 that pi and then depending if one PI is the main script 86 00:06:11,080 --> 00:06:16,970 meaning and calling one PI directly at the command line I will print this out else that means the variable 87 00:06:16,970 --> 00:06:21,920 name was not sent to Maine and I will print this out when that pie has been imported. 88 00:06:21,980 --> 00:06:30,670 So now let's work with our second file to that pie what do here is say import 1 and I will print out 89 00:06:30,760 --> 00:06:34,850 at the very top level. 90 00:06:35,080 --> 00:06:45,550 Let's print out something like top level in two dot pie and since I just imported one let's execute 91 00:06:45,550 --> 00:06:52,140 the function that's from one or say one that funk and here are going to have an if statement will autocomplete 92 00:06:52,150 --> 00:06:56,700 this if name is equal to mean. 93 00:06:56,890 --> 00:06:59,180 I will print two. 94 00:06:59,370 --> 00:07:06,110 The pie is being run directly else. 95 00:07:06,300 --> 00:07:14,450 Prince to the pie has been imported. 96 00:07:14,630 --> 00:07:18,810 So let's save the changes in both of these and then open up our command line. 97 00:07:20,310 --> 00:07:26,640 All right so the first thing we're going to do at our command line is actually run one up PI directly. 98 00:07:26,820 --> 00:07:27,620 So we run this. 99 00:07:27,660 --> 00:07:28,770 And we notice what happens. 100 00:07:28,770 --> 00:07:35,580 We get that print statement top level in one PI and then we see from that if name is equal to mean one 101 00:07:35,580 --> 00:07:37,210 that pi is being run directly. 102 00:07:37,320 --> 00:07:41,670 So we can see here that that built in variable underscore underscore name underscore underscore has 103 00:07:41,670 --> 00:07:43,950 been assigned that main string. 104 00:07:43,950 --> 00:07:49,440 So Paice on the nose and the entire script canel that one that has been called directly. 105 00:07:49,530 --> 00:07:54,270 But now let's check out Python to that pi. 106 00:07:54,270 --> 00:07:58,650 So now when I run this notifier happens I get back toplevel and one that PI. 107 00:07:58,890 --> 00:08:07,450 But now one that PI it's built in variable name has not been set to mean because it's been imported. 108 00:08:07,470 --> 00:08:13,350 So now we get back one that pi has been imported and then I get top level and to that pie funk in one 109 00:08:13,530 --> 00:08:16,620 pie and then to that Pye's being run directly. 110 00:08:16,620 --> 00:08:23,260 So that built in variable actually allows you to see whether something is being imported or run directly. 111 00:08:23,320 --> 00:08:29,130 So that's the idea in concept behind the variable name name and checking in physical to main. 112 00:08:29,140 --> 00:08:34,600 Typically however what you see is people they don't really do it the way we've done here with a check 113 00:08:34,920 --> 00:08:36,770 is something being run directly or not. 114 00:08:36,790 --> 00:08:42,980 Instead if we come back to Sublime Text Editor what they do is instead of having an L statement here 115 00:08:44,530 --> 00:08:50,880 since they just say if name is equal to me this is the same thing as saying run the script right. 116 00:08:50,960 --> 00:08:54,900 Because we already know that if this happens to be the case and someone is running one that PI script 117 00:08:54,900 --> 00:08:55,800 directly. 118 00:08:55,850 --> 00:09:00,650 So what they do is they define a bunch of functions up here or find their classes. 119 00:09:00,680 --> 00:09:03,290 So here's another function pass. 120 00:09:03,460 --> 00:09:08,420 You write some other function function to say and then down here at the bottom what you end up doing 121 00:09:08,420 --> 00:09:14,180 is you just call your function so you'll say OK execute function to then execute function 1 and then 122 00:09:14,180 --> 00:09:19,060 maybe have a little bit of logic here but the main idea is that this is more for code organization. 123 00:09:19,130 --> 00:09:23,330 You have all your functions and classes defined up here and then your logic where you actually execute 124 00:09:23,330 --> 00:09:24,640 things are defined. 125 00:09:24,680 --> 00:09:29,540 Here at the bottom and this is a really common structure you will see for larger that by scripts especially 126 00:09:29,540 --> 00:09:32,870 when you begin to use modules and packages. 127 00:09:32,880 --> 00:09:33,300 All right. 128 00:09:33,320 --> 00:09:35,000 That's the basics of this line. 129 00:09:35,000 --> 00:09:36,670 If name is equal to main. 130 00:09:36,710 --> 00:09:40,210 Definitely check out the explanation that textfile that goes along with this lecture. 131 00:09:40,220 --> 00:09:43,310 And if you have any questions feel free to post the Q&A forums. 132 00:09:43,310 --> 00:09:44,420 I'll see you at the next lecture.