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The string format method is very powerful and useful tool.

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You'll see it used a lot and you will use it a lot.

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It looks like this.

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Let's start by assigning a couple of variables a and b = 5 and 42.

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And then we'll print them out.

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If I were to just say print a, b like that then we get the numbers.

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But that's not terribly useful or descriptive.

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And you might want to look at it more like this.

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You might want to say this is and put in a placeholder and that is and put in

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another placeholder.

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And then use the format method and say a and b. And now you get a string,

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'this is 5 and that is 42.'

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So this is what the format method does.

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It allows you to put placeholders in a string and then replace those

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placeholders with values and return a new string.

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It's important to note that the string that's returned is a new string.

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Strings are immutable in Python.

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So this string is an entirely different string than that string.

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So if I had a string that just had this in it, do a copy and paste here, and say

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s = and put that in it.

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Now I have that string.

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If I just look at s, that's what's in it.

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If I say s.format(a, b), I get a new string.

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So the id of s is this.

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And if I say new = s.format(a, b) and look at the id of that, I have a different id.

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Those are two entirely different strings.

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So format returns a new string.

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It's also important to note that format is new as of Python 3.

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Format was not available in Python 2.

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In Python 2 things were done differently.

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In Python 2 you might have done some thing like this.

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this is %d, that %d. And then use a % operator and have a and b.

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So this was overloading the % operator and it was using C style format strings.

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And we just felt that this is obsolescent, and it needed to be replaced with

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something more powerful.

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And that's what happened in Python 3.

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The format method is more powerful.

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It's a more consistent syntax and it's actually a lot easier to use.

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One thing in particular that you can note here is that using this old way you

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needed to know a type.

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This %d represents a decimal type.

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And using this new way it uses the repr method, repr, to look at the value and

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decide what type it is and print it out based on its type.

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So you don't need to know what type the variables are in order to use format.

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Another thing worth noting is that this method that we are using here, and this

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gets used a lot in this course and you will see it a lot in new code with the

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bare curly braces, is actually new in Python 3.1.

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In Python 3.0, you needed some sort of a indicator inside of the curly braces,

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a positional indicator or a name indicator.

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And we'll look at how those work in a moment.

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But in Python 3.1 and later, you don't need anything inside of those curly

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braces, and it simply takes the positional arguments based on their order.

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So if I wanted to print a and b in the opposite order, I would actually have to

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put them in the opposite order in the format.

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I'd have to change them here, and say b, a and then I will get 42 and 5.

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On the other hand if I wanted to, I could say 1 here and 0 here, and not change

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their order and it will print them in the opposite order.

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So you can specify positional arguments inside the curly braces that will allow you, [00:03:49.1] for example if you wanted to print the same value several times, you could

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say, this is 1 and that is {0} and this too is {1}.format(a, b).

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And now I am actually getting this 1 value twice and the 0 value once.

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So these numbers represent the positional order in which the arguments

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are provided to format.

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You can also use names.

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You can say this is {bob} and that is {fred}.

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And then name your arguments in format. bob = a, fred = b and that can be useful.

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In fact you could put them in a dictionary d= dictionary, bob = a and fred = b

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and then use that dictionary.

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'this is {bob} and that is {fred}'.format and you use this double asterisk to

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refer to the dictionary.

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So format is very powerful in this way.

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And in fact, it's an extremely rich language all on its own.

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The full documentation for format is available on the Python

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documentation website.

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And it has all kinds of ways that data can be formatted and ways that you can specify type.

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It's an extremely rich language in its own.

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And it's actually more powerful and more flexible than the old way of

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doing things in Python 2. So that's format.

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These are the things about it that are essential to know in order to be able use it.

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You can get a lot of power out of it just knowing what I have shown you here.

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And in fact, nine times out of ten, this is all you are going to need in order

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to use format effectively.