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