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Python has some very powerful facilities for working with strings.

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And in fact, in Python 3, they become refined, and in some cases even more powerful.

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Let's get right into strings, and we'll start by making a working copy of variables.py.

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And we can call this variables-strings.py,

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go ahead and open that working copy,

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and we'll start by defining a String.

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I'll just call it s, and I'll say 'This is a string!' and we'll go ahead, and

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we'll print(s) and save that and run it.

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And there we have the string.

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Strings in Python are immutable objects,

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and they're created with either single quotes or double quotes.

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And so if we change those single quotes to double quotes, we'll see - if we

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save and run, we'll see that we get exactly the same result.

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You can use Escape characters in a string, as you can in many languages.

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So if I put in here a \n, that'll introduce a new line in the middle of the string.

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And if I save that and run it, we see that there is a new line now between the a

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and the s of string.

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On the other hand, if I want this \n to actually be a part of the string, rather

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than getting replaced with a new line, I can put the letter r before the

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definition of the string like that,

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and if I save that and run it, I get the \n as part of the string.

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This is called a raw string, and the place where this gets used the most is when

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creating regular expressions.

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And we'll get into regular expressions in some detail in another chapter.

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In addition to these sorts of Escapes with the backslashes, you can also do some

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formatting and replacing of variables in the string.

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For example, if I create a number and call this, say n, and give it a value of

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42, I could put that 42 right in the middle of the string here.

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And I'm going to show you the Python 3 way to do this.

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And we'll look briefly at the Python 2 way to do it as well, because you'll see that a lot.

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For all your new code, you want to use the Python 3 way, which is with the

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format method of the string object, because the Python 2 way is going to go away.

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It's considered obsolescent, and it will be dropped in the next version of Python.

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So I'm going to save this and run.

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And you'll see what this does.

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This actually inserts the value of n in the middle of the string.

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We have these curly braces here, and those get replaced with the format.

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So format is a method of the string object.

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And so this literal string is actually an object.

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Remember, everything in Python is an object.

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We can use this objecty-referencing operator, this period, to access a method

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of that object, and do this variable replacement.

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So this is very powerful, and this is very common.

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And you'll see it done this way in new Python 3 code.

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In Python 2 code, you'll see it's done this other way.

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I'm going to put %s here, and over here a % sign and the letter n. And so we'll

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save that and we'll run it.

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And you see we get the same result.

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This is the way that it was done in Python 2.

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And this is a bit of a hack.

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It's perfectly valid, and you'll see it a lot.

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You'll even see it some in Python 3 code that's written by people who are used

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to Python 2, and that's fine.

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The reason you don't want to use this construct is because it is considered

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obsolescent, and it will be dropped in the next version of Python.

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So you'll see this, you want to know what it does, but the right way to do it in

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Python 3 is to use the new format method of the string object.

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And that will look like this.

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I'll save that and run it.

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And that's how that works.

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There's one more way I want to show you for defining a string, and this is

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using the triple quotes.

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And you can triple either the single quotes or the double quotes.

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So I can either do it this way, or instead of these triple quotes, I can do it

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this way with the double quotes, like this.

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And you'll see it's done both ways.

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I tend to use the singles tripled instead of the doubles tripled.

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Now what this does is it allows you to have a string that spans several lines.

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And so, what I'll often do is I'll start with a backslash and a new line and go

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all the way back to the end of the line like that,

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and this will allow me to just have line after line of text and more text,

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and to have it actually started at the beginning of it.

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I'll explain what this does in a moment.

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Let's save this and run.

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And then you can see what this does.

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This is useful if you have lines and lines and lines of text.

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And so the way you do this is with three quotes, either single quotes or double

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quotes, at the beginning and the end.

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And the result will be a string that has the new lines, and it's all formatted

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exactly like you type it in.

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What this here does, this backslash and a new line, is that it escapes the new

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line, so that it doesn't actually show up in the string.

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If I didn't have this, and I save this and run it - that's scrolled out of the way -

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there you see that we get a black line at the beginning, because this blank line

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here is actually inserted in the string.

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The way to get that not to happen is to use the backslash before it.

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The backslash has to be the very last character on the line, so that it's escaping

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the new line and not a space or something.

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So I save that and I run it,

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and you can see that we don't have a scrollbar over here.

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This is actually at the top,

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and there is no new line at the beginning of the string.

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So that's the triple quote way of defining strings.

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And that's often used in docstrings in function, which we'll get to later on in

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the chapter on functions.