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Python 3.6 introduced another way of
formatting values in a string.

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These are called f-strings or formatted string literals. Now at the moment I won't be

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using f-strings in the course. That's
because there's no plans to back port

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them to earlier versions of Python 3.
Python 3.4 is still very common,

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and f-strings won't work with that version, or
earlier versions. But with that said,

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it is worth being familiar with them. So let's
have a quick look. I'm going to use the

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strings.py file from an earlier
video, so I'm going to select that,

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and we're going to work with this file. Now at the moment, we've got an error on the last line.

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I used that to demonstrate that you
can't concatenate a string and an int.

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So let's firstly just check this by running
it again, confirming we've still got the error.

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And you can see we've still got this type
error "can only concatenate strings,

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not an int to string".

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So let's fix that using
an f-string. So all we really need to do

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to fix that, is to put the letter f
before is up here. Put an f before the

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double quote and that's literally all we
need to do. So an f-string is defined

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by putting the letter f before the
opening quotes. Now that we've done that,

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we can use a variable name, inside curly
braces, in a similar way that we've used

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replacement fields. So what we can do is
delete this extra double quote here,

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come up and put age there. We can put age in
left and right curly braces, like so.

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We can remove the other double quote there,
so we've got it all in the one string, now

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So as you can see, it looks very
similar to a replacement field. It's a lot

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cleaner, because we don't have to use
.format at the end anymore. So if we run

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the program, let's do that just to make
sure that it works, and you can see we've no

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longer got an error. The output is
showing Tim is 24 years old - and Tim

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wishes he was 24 years old. Alright, so
all the formatting for replacement

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fields also works with f-strings. So, for
example, I could do some formatting

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along these lines. So let's just type
some code in. So on line 24 I'm going to type

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print parentheses f double quotes Pi is
approximately,

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and then in left and right curly braces,
noting that the right one's added for us

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automatically, I can type in an
expression 22 / 7:12.50f, and then we've got

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our double quote and then our right
parenthesis. Now clearly you can see that

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I've used an expression rather than a
variable name there. So let's just try

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running that first, and you can see we've
got the value showing.

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Now what we can also do is calculate 22 / 7 first, and then use a variable,

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so let's do that.
So PI on line 25 is equal to 22 divided

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by 7. Line 23, we'll do a print parenthesis f
double quotes Pi is approximately

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and left and right curly braces, and this
time we'll use the variable, so pi:12.50f

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for formatting,

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and, sorry for precision,  and then we'll run that again,

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and you can see we've got the
identical output. So now that you

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understand replacement fields, you can
change to using f-strings instead, if you

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want. But be aware that your code won't
run on Python 3 versions, earlier than 3.6,

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if you do use them. In the next video,
we'll finish this section with a quick

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look at yet another way to format strings.

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See you in the next video.