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Accessing Keys and Values
4:07Discover how to access data from a Python dictionary
In this video, we're gonna talk
about how to access keys and
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values from inside a Python dictionary.
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Do you remember how I mentioned
previously that unlike sequences,
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which are indexed by numbers,
dictionaries are indexed by their keys?
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We can use that difference to transfer
what we know about accessing values in
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sequences, to accessing values in
dictionaries.
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You see here in my workspace,
I have a simple Python list.
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Without any context, the data stored in
this list doesn't make a lot of sense,
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which is why soon,
we're gonna convert it to a dictionary.
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But, for right now, let's refresh
how we get values out of this list.
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If I want the first element in the list,
I'll use the code course,
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then square brackets, and then
the index of the value I want to grab,
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in this case, let's say zero.
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The same syntax is used when
pulling values from dictionaries.
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Except instead of putting a numerical
index inside the square brackets,
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we put the value's key.
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So first let's back up and
convert this list to a dictionary.
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To do that, I'll first change the square
brackets here to curly braces.
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Then for each value in this I'll add
a key, which is kinda like a label
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Now to access that first value again,
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I'll just change this code here
to reflect the correct index.
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And now I'll wrap that in a print
statement, and then I'll save and
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run the file to show the output.
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Let's save.
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Yep, it printed out Ashley.
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So that the basics of accessing
an individual value from a dictionary.
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It's very similar to accessing
an individual value from a sequence.
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It's important to know that if you attempt
to access a value with a non existing key,
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Python won't just skip over it,
you will get an error.
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Now, Python also has ways to
grab a list of all the keys or
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all the values from a dictionary.
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And even a built-in function to sort
those lists into lexicographical order.
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You might have learned about
lexicographical ordering before, but
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check the teacher's notes for more info.
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So let's move down to the terminal where
we can work a little more efficiently with
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our dictionary.
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I'm gonna start the interpreter and
copy the dictionary down there.
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So, first, to get a list of all
the keys in the dictionary,
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I'll use the keys method.
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To use that I type the name of the
dictionary which is course then dot and
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then keys, the name of the method,
and then parens,
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just like a regular function call.
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When I hit Enter, it will show
the return value from the keys method.
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Yep, here's a list of every key,
teacher, title and level.
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Similarly, we can access a list of every
value in the dictionary using the values
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method.
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That's course.values().
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And yes, that returned the list
of every value, Ashley,
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Introducing Dictionaries and Beginner.
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Both of these methods returned just plain
lists that can be iterated over using
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a for loop.
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Now, if for
some reason we needed these lists sorted,
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we could wrap them in a call to
the built in python function, sorted.
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Which will return a copy of the past
list back in lexicographical order,
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which in this case, just means it
will be sorted alphabetically.
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Let's clear this and take a look.
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That returned a list of
the alphabetized keys.
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And then to do it again for values.
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There we go.
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Okay, now that we covered
accessing keys and values,
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join me in the next video to learn about
updating and mutating dictionaries.
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