Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
Patterns, sets, groups, oh my! Now that we have so much control over what our patterns find and what we can create from the Matches we get back, let's look at a way to turn regular expressions into a variable and then loop over our results.
New terms
-
re.compile(pattern, flags)- method to pre-compile and save a regular expression pattern, and any associated flags, for later use. -
.groupdict()- method to generate a dictionary from aMatchobject's groups. The keys will be the group names. The values will be the results of the patterns in the group. -
re.finditer()- method to generate an iterable from the non-overlapping matches of a regular expression. Very handy forforloops. -
.group()- method to access the content of a group.0or none is the entire match.1through how ever many groups you have will get that group. Or use a group's name to get it if you're using named groups.
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
Eventually, you're going to be in a
situation where you need to
0:00
use a pattern on 100 different items in a
big loop.
0:02
Or maybe it'll be 500, or 1000.
0:05
You don't wanna have to build and match
the pattern every single time.
0:08
So the regular expression library has
given us a way to compile a pattern into
0:11
an object that we can match against.
0:15
Let's look at how to do that.
0:17
We've already seen that we can make
patterns as strings.
0:18
We stored them as a variable back, way,
way back in the first video.
0:21
But, that's not really the most useful
thing in the world.
0:25
I mean like, if we have, say this string,
yeah, it's handy having this as
0:27
a variable, but it doesn't save us a lot
of time or trouble.
0:32
It'd be better if we could say that
pattern in a state where it
0:36
was ready to go.
0:40
It's ready to be used as a regular
expression.
0:41
And we can do that.
0:44
That's what the Compile method let's us
do.
0:46
So that's actually change line here.
0:49
Instead of Search, we'll wanna say
Compile.
0:52
And what that does is this is gonna take
the regular expression and compile it,
0:55
get it ready for use.
0:59
Now the one other thing we have to change,
is we have to take out where it says data.
1:01
Because when we compile a regular
expression,
1:06
we don't compile it with the data it's
gonna be run against.
1:08
It's like making the regular expression a
bit more generic.
1:11
We can now run it against a lot of
different things.
1:13
Not just the one thing that we did the
search against, or the match or whatever.
1:16
So, I'm gonna take out this line one and
let's look at this one.
1:21
So we've got line.groupdict and
1:24
that no longer makes sense because line
isn't a match.
1:26
So let's go ahead and do a match.
1:29
We'll do re.search, line, data, and then
groupdict.
1:31
So what we did here, is we created a
regular expression search,
1:39
just like before, and we said, okay, your
pattern is this compiled one, it's line.
1:43
And the string you're gonna match it
against is data.
1:49
And now notice, we didn't specify any
flags.
1:51
You specify the flags when you do the
compile, not when you do the search.
1:54
So let's save that and let's Run.
1:59
And there we go, we got that same thing.
2:03
So, that's great.
2:06
But what's really, really, really cool,
2:07
at least I think so, is we don't have to
do this re.search stuff.
2:10
What we can do, instead, is we can just
use line directly.
2:14
[BLANK_AUDIO]
2:19
So we can just say, okay, take line.
2:23
It's a pattern.
We know it's a pattern.
2:25
Do a search with it against data.
2:27
So let's take that out.
2:31
Run this again, and we should get the
exact same content, and we do.
2:33
So, that's pretty cool.
2:37
But, we've only got one thing.
2:39
We're only, we're only getting my line.
2:41
How do we get the rest of the lines?
2:42
Well, this is the last part of the r-a
library that I wanna go over with you.
2:44
But there's still more in there to
explore.
2:49
Go check the docs.
2:51
They're awesome.
2:52
It's a method that's named finditer.
2:53
And it gives us back an iterable of each
non-overlapping match.
2:55
It's kind of like giving us back a list,
but it's not exactly a list.
2:59
It's also kinda like using Find All, but
instead of getting back topples,
3:02
we get back a match object, like when we
use re.match or re.search.
3:07
So let's try this out.
3:11
Let's come back up here and let's say for
3:13
match in line.search, oops sorry.
3:18
Not line.search.
3:22
Line.finditer against data.
3:24
We want to print match.group.
3:29
Name.
3:32
So, this .group method,
3:33
when you have a match object says, show me
whatever is inside of the group.
3:36
Now, I can say, group with a, with
nothing, and
3:41
it'll show me the whole thing that it
captures.
3:44
I can do group with a number, and it'll
show me the group at that index.
3:47
So, 0, 1, 2, so on.
3:50
Or I can give it a name and it'll show me
the group at that name.
3:52
All right, so let's try that out.
3:56
So there we go.
4:00
There's everybody's names.
4:01
You can see Ryan Carson, The Doctor,
Exampleson, Example, so on.
4:03
All right, that's all of our names.
4:06
We can of course ask for any group that we
want or do all sorts of other stuff.
4:09
For example, let's make a fully qualified
email to headers.
4:14
You, you've seen this before where it's
like a name and then less than,
4:17
their email address and greater than,
right?
4:21
Okay, so before we do that,
4:23
I want to actually come back and edit our
pattern, and add two things.
4:25
So what's cool is we can have subpatterns,
or subgroups, sorry.
4:30
So we can do here last, and that's the
last name.
4:34
And we can do here first, and that of
course is the first name.
4:42
So there's our first name, there's our
last name, as these little sub patterns.
4:49
'Kay?
4:52
So now in our.
4:53
For loop, we need to print out a new
thing.
4:55
And let's print out first, last, email.
5:00
'Kay.
5:09
And we wanna format this.
5:10
With the match.groupdict.
5:12
Right?
It'll go ahead and
5:17
find those keys in the groupdict, it'll
use those as keyword arguments.
5:19
All right, so let's try this out, we
should have email addresses for everybody.
5:26
Check it out, we've got email addresses.
5:30
There's the name, and an email address.
5:32
That works pretty well, and it's a lot
simpler than I
5:35
would have actually expected it to be if
you were just like hey,
5:38
turn this into a bunch of email addresses.
5:41
Hopefully this will give you some ideas on
how to take our address book further.
5:43
You can build all sorts of things out of
dictionaries.
5:47
Made from strings through regular
expressions.
5:50
In this course, compiling our pattern
doesn't actually save us a lot of time or
5:53
memory, but it's a good habit to get into,
so
5:56
you won't forget to do it when it actually
matters.
5:59
And using things like finditer helps us to
save even more memory.
6:01
Compiling patterns also lets you make
patterns available for
6:06
import in other parts of your
applications, or even in other packages.
6:08
This way, you can make your pattern as
perfect as possible in just one place and
6:12
reap the benefits anywhere else that you
need it.
6:16
I think we're done.
6:18
We've gone over pretty much every area of
regular expressions in Python, and
6:20
we've turned a block of text that no one
would want to wade through into super
6:24
useful dictionaries that we can put into
classes or transform into a new text file.
6:27
In fact, that's your extra credit for this
course.
6:32
Take the regex we wrote and the text and
make a class for
6:34
a person to find by the data.
6:37
Give them names and a phone number and an
email address.
6:39
Maybe make another class for an address
book that collects all these
6:41
people together and let's the user search
them.
6:44
Be sure to share it on the forums.
6:46
Thanks so much for being part of this
course.
6:48
I'll see you next time.
6:50
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up