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Add and change values in Python dictionaries.
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Welcome back.
0:00
The topic of discussion for this video
is updating and mutating dictionaries.
0:01
Dictionaries are mutable,
that means we can change them in place.
0:05
And these changes are done using
syntax we've already covered.
0:08
Let's keep working with our previous
example down in the console.
0:12
The course dictionary here
has three key value pairs.
0:16
To change the value for any of these keys,
we access it using the key.
0:19
And then,
like we assign a value to a variable,
0:22
we assign a new value to the key.
0:25
So say I want to change the value for
the teacher key.
0:27
First, I'll access the value.
0:30
Then I assign it a new value
using the equals sign.
0:35
Now this code will override
what's in the dictionary.
0:42
If we inspect the contents
of the dictionary now,
0:45
we'll see that Ashley is no longer
the value associated with the teacher key.
0:47
The new value is Treasure.
0:53
Take a moment to try this on your own.
0:55
After opening the attached workspace,
pause the video here and
0:57
try to change the value of the level
key from beginner to intermediate.
1:00
When you're done, unpause the video and
I'll show you the solution.
1:04
Welcome back, were you successful?
1:08
To change the value of the level key,
1:11
we access it using course['level'].
1:15
Then we assign it a new value.
1:20
If we inspect the course dictionary now,
1:27
we could see the new value has
overwritten the previous one.
1:29
Great, now adding an entirely new
key value pair to the dictionary
1:34
uses the exact same syntax.
1:39
Let's say I wanna add another piece
of data stages to the dictionary,
1:41
that's the number of stages in the course.
1:45
Just like when updating a keys value,
I use course then square brackets and
1:47
then the name of the new key,
in this case stages.
1:52
And then I assign it
the value I want it to have.
1:58
This works because if Python can't
find a matching key to update,
2:03
it will simply create a new key
value pair inside the dictionary.
2:06
So let's check out
the course dictionary now.
2:10
We can see our new key value pair
stages with the value of 2 inside.
2:14
Give this a try yourself,
pause the video here.
2:19
In the attached workspace, add a new key
value pair to the provided dictionary.
2:22
The key and
value can be whatever you like.
2:26
But make sure you test that it worked
by saving and running your program, or
2:28
by copying and pasting
the dictionary into the terminal and
2:32
working directly from there.
2:35
When you're done, unpause the video and
we'll keep going.
2:37
If you have a question, please feel free
to reach out in the Treehouse community.
2:39
All right, let's keep going.
2:43
Now we're gonna talk about removing
key value pairs from a dictionary.
2:45
This is done using the built-in
Python function del for delete.
2:49
Del accepts one argument,
the value that you want removed.
2:52
So say we no longer wanted
the stages key value pair we
2:56
added just a few moments ago.
2:59
To delete it, we call the del function,
and then pass the value as an argument.
3:01
Let's inspect course again.
3:15
Great, the stages key value pair is gone.
3:19
Congratulations, you've now completed the
first stage of introducing dictionaries,
3:23
celebrate your accomplishment.
3:27
In the next stage, we'll continue our
discussion by learning about how to
3:29
iterate over dictionaries,
and packing and unpacking.
3:31
See you soon, and keep on coding.
3:35
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