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[MUSIC PLAYING]

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SPEAKER: Well, hello, one and all, and
welcome to our short on capture groups.

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Now, those of you who have
made international calls

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might be familiar with what's
called a country calling code.

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And I have here three of them up above
in a dictionary called locations.

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I have 1 plus 1, which
often involves numbers

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from the United States and Canada.

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I have 1 plus 62, which often
involves numbers from Indonesia,

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and 1 plus 505 that involves
numbers from Nicaragua.

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And I have down below here, in
main, a program that in this case

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validates phone numbers internationally.

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So I have here a pattern
that I'm going to look

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for within each of
these phone numbers I'm

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going to enter into my
program down below on line 7.

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In this case, notice what I'm expecting.

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I'm expecting the literal
actual character plus here.

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I've escaped it with this backslash
because plus has other meaning

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meanings within regular expressions.

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I'm not expecting any kind of
number, in this case, 0 through 9,

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between 1 and 3 times.

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So notice here, the country code for
the US and Canada, that's plus 1.

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So only one number here.

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For Indonesia, it's two, 62.

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And for Nicaragua, it's three, 505.

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So between, in this case, one and
three numbers following some plus.

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Thereafter, there will hopefully
be a space for this invalid number,

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and then there will be exactly three
numbers, a dash, again, exactly three

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numbers, followed by a dash again,
and then exactly four numbers.

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So this is the pattern
we are looking for.

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And down below, on lines
9 through 13, well, this

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is the code doing that work for us.

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We've stored, within number, the user's
phone number that they have entered,

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and we're going to
check, using re.search,

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if we found a match for our
pattern within the number string.

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If we do have a match is returned
to us, we'll print valid.

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If we don't, we'll print invalid.

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Let me go ahead, down below
here, let me type "main"

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to ensure I call main
when I run this program.

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And I'll go ahead and
run Python of groups.py.

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And if I hit Enter, now I should
be able to enter a number.

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I'll test one here, plus 1.

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And I'll type in that 617-495-1000.

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I'll hit Enter here, and
we'll see that is valid.

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Maybe I'll try it, too, for Indonesia.

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I'll do plus 62, and I'll
enter in my phone number again.

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And I'll hit Enter, and I'll
see if that's valid as well.

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And just for good measure,
I'll test Nicaragua.

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I'll do plus 505, and
I'll type in this number,

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and we'll see that is valid as well.

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So it seems like our pattern
is working, but there's

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more we could do with this program,
I think, thanks to this feature

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called a capture group.

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Well, maybe what I want
to do is not just share

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if this number is valid
or invalid, but maybe tell

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somebody from what country, in this
case, this number is calling from.

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You can think of your phone.

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When it receives some call
from an unknown number,

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it might at least tell you the location
or the area that number is calling from.

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What if we could write
the same thing here

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where people call us internationally
and we show the user,

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in this case, what country
they are calling from?

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Well, in this case, we
don't want to just test

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to see if we find the pattern
within our phone numbers here.

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We also want to extract
some portion of it,

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in this case, the very first
portion, the country calling

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code-- plus 505 for Nicaragua,
plus 62 for Indonesia,

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or plus 1 for the US and Canada.

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But we run into a problem here if we to
use maybe simple a string manipulation.

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If I enter in some number
and was trying to extract,

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in this case, the country calling
code, well, I wouldn't immediately

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know whether I should extract, in this
case, the first two characters, plus 1,

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the first three characters, plus 62, or,
in this case, the first four characters,

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plus 505.

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But thankfully, I actually use
regular expressions and capture

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groups to dynamically capture the
portion of the content I'm looking for.

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Now, the way I can make a capture
group is by using parentheses inside

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of a regular expression.

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So really I want to capture
or extract, in this case,

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the country calling code, which we
said the pattern exists for right here,

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a literal plus sign
followed by on to e numbers.

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Now, I can encase this
inside of parentheses,

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and this becomes my own capture group.

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But how could I maybe find
the information I capture?

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Well, if I find a match here, turns
out that this match object in Python

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comes with another one called group--

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group.

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If I were to do--

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let me do match.group.

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Well, this would help me find
all of the capture groups

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I've actually implemented
in my regular expression

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and extract them from this match.

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Because, let's say, this is the
first capture group we have,

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I could go ahead and type 1 here.

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Capture groups, at least in Python, in
this particular case, are one index.

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So I'm saying here, if there is
a match, go ahead and give me,

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in this case, the result that I
found within the first capture group.

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I'll go ahead and store this in
a variable called country_code.

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And I could-- instead
of printing valid here,

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maybe I'll go ahead and print
something like country_code

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and see what we can find.

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Well I'll go ahead and
run Python of groups.py,

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and I'll go ahead and do plus 1,
followed by my phone number, hit Enter.

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And now we'll see plus 1.

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So it seems like we extracted, in
this case, the portion of our content

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that matched the pattern
within these parentheses.

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I'll try it with another one here.

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I'll do Python of groups.py plus 62.

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And we'll see plus 62.

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So it is dynamic.

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And it's not looking for the
first two characters all the time

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or the first three
characters all the time.

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It's looking for this pattern.

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And when it finds it, it's
returning it to us as appropriate.

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Now, what else could we do with this?

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Well, country_code
literally is a string here.

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So if I wanted to, in this
case, find the country somebody

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is calling from based on their
country calling code, well,

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I could perhaps use country_code as
the key for this dictionary here.

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I could type locations bracket
locations bracket country_code.

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And because each of these country
calling codes is a key in my dictionary,

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I should hopefully find, in
this case, the actual location

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they are calling from.

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Let's try this out.

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I'll run Python of groups.py,
and I'll now type-- oops.

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I'll now type-- let's do plus 1 again,
followed by the number, hit Enter.

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And now we'll see United
States and Canada.

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I could do this again.

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I could try, let's say, a
plus 62 and number again--

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Indonesia.

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I'll now try plus 505,
and I'll see Nicaragua.

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So the capture group
here is doing the work

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of finding the portion of
our content that matches

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some pattern we were looking for.

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Well, I think we've really seen
a lot of what this can do for us,

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but there is one more
feature to take a look at.

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Here, notice how on line 11 I am
really using indices, indexes, to find

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the capture group I'm looking for.

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But a more complex regular expression
might involve more than one

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capture group, could involve up
to, I don't know, more than one,

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two, three, four, could get up to 10.

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However many it is, it can be
helpful to have a better way

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to refer to these capture groups.

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So if this capture group has
some particular meaning to it,

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I could actually give it
a name to refer to later

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on within the regular expression.

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And the way I do this is
with the following syntax.

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Within my capture group, after the first
parentheses, I can type question mark p

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and then open bracket close
bracket, or, in this case, less than

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sign, greater than sign, and then
some name for this capture group.

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I could call this
country_code just like this.

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So now this pattern here
and the capture group

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has a name I can refer to
later to extract it with.

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Down here on line 11, I
could, in this case, use 1,

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but now I could actually make
use of country_code, the name I

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gave for this particular capture group.

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And I could type in
country_code just like this,

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which will say, find for me, in this
case, the capture group that I named

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country_code and use that instead.

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I'll type Python of groups.py.

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I'll go ahead and type
plus 1, same number here.

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And now we'll see United
States and Canada.

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Seems to work but is now a little more
readable, even some name something

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that we might later hope
to capture in our programs.

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So this was our brief
foray into capture groups.

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And this was our short.

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We'll see you next time.

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