Python Variables and Print()

Quick reference

• 00:05 Okay, in this video I want to talk about variables.
• 00:07 And variables are one of the most key fundamental things in computer
• 00:10 programming.
• 00:11 Every program you ever create will have lots and lots of variables.
• 00:15 And a variable is like a bucket.
• 00:17 It's a box, it holds things.
• 00:18 And they can hold all different types of things.
• 00:20 They can hold words.
• 00:21 They can hold letters.
• 00:22 They can hold numbers.
• 00:23 They can hold other variables.
• 00:25 They can hold lists.
• 00:27 They can hold tumbles.
• 00:28 They can hold dictionaries.
• 00:29 We don't know what any of those things are, but
• 00:31 we're going to learn them pretty soon.
• 00:32 They're just all around very important items.
• 00:36 So in Python to create a variable all you have to do is name it.
• 00:39 So I'm going to call this one first underscore name, all right?
• 00:43 So this is now a variable.
• 00:45 And to assign something to it, we use an assignment operator.
• 00:48 In this case, the equal to sign.
• 00:51 And then we can just put whatever we want in there.
• 00:53 So I'm going to type in John.
• 00:55 So now we've created a variable, first_name.
• 00:58 And we've assigned some text, which Python calls strings.
• 01:03 We've assigned this string, a string of characters to this variable.
• 01:07 So now anytime we reference first underscore name, we are referencing John.
• 01:13 So we can come down here and we can for instance, print it out.
• 01:16 So we can print first underscore name.
• 01:19 So let's go ahead and save this control S to save it,
• 01:22 headed back over to our terminal.
• 01:25 And let me clear the screen.
• 01:27 And let's run this file Python Hello.pi, and it says Hello World and
• 01:32 then it prints out John, which makes sense.
• 01:35 We told it to just print out John.
• 01:36 Now I can comment out this line, this little hashtag,
• 01:40 this number sign this comments things out.
• 01:44 Comments are useful in that we can describe what our texts, what our code is.
• 01:49 So for instance, I could go a create variable to hold first names, right?
• 01:55 So this is a comment.
• 01:57 So Python will ignore this, but it's good for
• 01:59 us as we look back over our code in the future.
• 02:02 It helps us know what we were doing when we actually wrote the code.
• 02:06 So you can see we've created this first name variable.
• 02:09 We've called it John, and we printed it out.
• 02:11 So very cool.
• 02:12 Like I mentioned, you can assign anything to variables.
• 02:15 So let's call, let's create another one called favorite underscore number.
• 02:20 Let's set that equal to 41.
• 02:21 Now you notice this time I didn't put quotation marks around
• 02:25 it because with text, we always put quotation marks around it.
• 02:28 With numbers we don't.
• 02:30 So now we can just come down here and just like before,
• 02:33 instead of first name, we can print out favorite number.
• 02:38 So let's head over to our terminal and run this guy.
• 02:41 And you can see it prints out 41.
• 02:43 Notice it did not print out John.
• 02:46 We've created a variable.
• 02:48 We've set John in it, but
• 02:49 we're not actually doing anything with that variable.
• 02:52 We're not printing it out.
• 02:53 We're just printing out favorite number.
• 02:55 So it's sort of there.
• 02:56 It's in our program.
• 02:57 It's been saved to memory, but we haven't actually used it and
• 03:00 we can use it later on if we want.
• 03:02 But that's how that works.
• 03:04 So variables, like I said, are just super important and
• 03:07 creating them is just as easy.
• 03:09 Now let's take a look at how I name this thing.
• 03:12 You'll notice I put an underscore between these two words.
• 03:16 I could just as easily have done it like this, but
• 03:19 that's not the convention in Python.
• 03:21 And if you think about it, this is really kind of hard to read.
• 03:24 It's a good idea to separate these things somehow.
• 03:27 And so we separate them with underscores.
• 03:30 You cannot use spaces.
• 03:32 Python won't know what to make of this.
• 03:35 It has to be connected with something.
• 03:36 Now you might be tempted to do something like that.
• 03:39 You can't really do that because that's the subtract sign, right?
• 03:43 Just like the addition sign.
• 03:45 So in this case, Python would try to subtract number from favorite,
• 03:50 and it would get very confused by trying to do that.
• 03:54 So, there are some characters we can't use when naming a variable.
• 03:58 You also wouldn't go favorite plus number, right?
• 04:01 For the same reasons, but underscores work well.
• 04:04 Some people like to do something called camel case,
• 04:07 which would be something like favorite number equals 41.
• 04:11 And you notice we call it camels because the second number is always capitalized,
• 04:17 sort of like the hump of a camel, right?
• 04:19 A lot of programming languages use this.
• 04:22 I know this is popular with JavaScript, they like to do things like this.
• 04:25 Python generally doesn't use camel case.
• 04:28 I mean you can, it's perfectly valid, but
• 04:31 the convention is to use underscores when using more than one word.
• 04:35 Also mention when naming variables, try to be as descriptive as possible.
• 04:40 You'll notice up here, we're saving a first name, so I called it first name.
• 04:45 I could just as easily have called this variable, 31
• 04:50 equals John, right?
• 04:55 This is valid too.
• 04:57 But this doesn't tell me anything, variable 31.
• 04:59 I don't know what that is.
• 05:01 On the other hand, I know exactly what first name is.
• 05:03 It's likely to be a first name, right?
• 05:06 So you want to be as descriptive as possible when you're creating variable
• 05:09 names, and it just makes life easier.
• 05:11 So finally, you'll notice this is lowercase and not uppercase.
• 05:15 You can use uppercase,
• 05:16 but again, the convention is to use lowercase when naming variables.
• 05:21 It's just sort of what Python people do.
• 05:22 Uppercase works, this is valid, but the convention is to use lowercase.
• 05:27 So that's a crash course in variables.
• 05:29 We'll use these throughout the course and you get very familiar with them and
• 05:32 very used to using them, and really not much to them.
• 05:35 Just remember, they're sort of like a box.
• 05:37 They're a bucket, you can put things in, you can take them out,
• 05:40 you can use them again.
• 05:41 You can add new things in later on, you can delete what's in there.
• 05:44 And we'll get into all that if we need to throughout the course.
• 05:47 But really, this is all you need to know about variables right now.
• 05:50 And that's all there is to it.
• 05:52 So in the next video, we'll start to look at the Python list.

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