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
Count and Index are two other Python sequence methods that give us useful information about our sequence data.
This video doesn't have any notes.
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
In addition to membership testing, we can
also use methods to determine how many
0:00
times a given object
appears in a sequence.
0:04
And then finally, where or what index
a particular object falls in a sequence.
0:06
A method is just a function that
is called on a specific object.
0:12
Sequences, like most everything in Python,
are objects.
0:15
And they have special methods
that can be called on them.
0:18
For the first part of this video,
we'll be talking about the count method.
0:21
Count is a built-in sequence method.
0:25
It receives one argument,
the object that we're counting.
0:27
Let's pick up with the last example.
0:30
Now that we know the string
tuple is inside docs,
0:32
let's figure out how
many times it appears.
0:34
To use the count method,
0:37
we'll first provide the sequence
we wish to count from.
0:38
Then we have a dot and
then the name of the method,
0:42
Followed by parens,
just like with regular functions.
0:48
And then we pass in our argument,
which is the string tuple.
0:51
All of this code together says that we
want to know how many times the string
0:55
tuple occurs in docs.
0:59
I'll wrap this in a print statement so
we can see the result, and
1:01
then I'll save it and run it.
1:03
Okay, the Python interpreter says that
the count method returned the number 1,
1:17
meaning the string tuple appears
in this excerpt one time.
1:21
But I'm looking at it right now, and
I see tuple in there three times.
1:24
Is the method wrong?
1:30
Nope, all of these operators and
methods are looking for exact matches.
1:32
When it comes to strings,
that means everything is case sensitive.
1:35
This excerpt only includes the string
tuple with a lower case t one time.
1:39
Both other times,
tuple begins with a capital t, and
1:43
thus aren't considered a match.
1:46
See the following instruction step for
1:48
more examples on how to use count
with different sequence types.
1:50
Python also gives us a way to find the
index of the first occurrence of an object
1:54
inside a sequence.
1:58
This is done using the index method.
1:59
The syntax is very similar
to the count method.
2:01
And just like the count method,
2:04
the index method takes a single argument,
the object we want to find.
2:05
So in our example here,
I'll just change count to index.
2:09
Then I'll save it and run it.
2:15
Cool, it printed out 105.
2:20
What does that mean?
2:22
It means that the lowercase string tuple
is first found at the 105 index in
2:24
the docs string.
2:28
Or in other words, our matched tuple
string starts at the 106th character.
2:30
I'm gonna erase all this and
2:35
show another example of the index
method with a short list.
2:36
Here, I'm going to make an alphabetized
list of a few Treehouse teachers.
2:43
I want to find the index that
Nicole appears in this list.
3:00
So to do that, I'll do teachers.index,
3:03
and then I'll pass Nicole as my argument.
3:08
I'll wrap this in a print statement.
3:15
And then now we'll run.
3:20
Okay, this code printed out the number 2,
3:28
meaning that the index of the item
that matches Nicole is 2.
3:30
That makes sense, we can see that Nicole
is the third element in the list.
3:34
So what happens if we add Nicole's
name to the list a second time?
3:38
Let's run this again.
3:47
It's still printing out 2.
3:51
That's because the index method only
returns the index of the very first
3:53
occurrence of an object, no matter how
many times its present in a sequence.
3:56
And now what happens if we delete
the Nicole items from the list altogether?
4:01
Okay, we're getting a ValueError.
4:16
It says, 'Nicole' does not exist in list.
4:18
This is important to remember.
4:21
If you're using this method,
always account for
4:22
the fact that if the object doesn't exist,
you'll get an error, not an integer.
4:25
And your code won't run.
4:29
All right, when you're ready, join me
in the final video of Python Sequences
4:31
to learn about concatenation and
multiplication.
4:34
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