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Iterate over Dictionaries
4:14Learn how to iterate over dictionaries using for loops.
[MUSIC]
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Welcome to stage two of
Introducing Dictionaries.
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In the second half of this course, we'll
be discussing iteration, packing, and
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unpacking.
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Iterating over dictionaries uses a for
loop, just like iterating over sequences.
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So continuing on with
our previous example,
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here we have a simple
dictionary called course.
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Let's write a basic loop to
iterate over the dictionary.
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It should look very similar to a for
loop used to iterate over a sequence.
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Let's save and run and
see what this prints out.
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Okay, this may not have been
exactly what you expected.
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As you can see,
only the keys were printed.
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It didn't give us the key value pair or
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anything regarding the values
in the dictionary at all.
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To access the value for
each key as the loop progresses,
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one option is to use
the syntax you learned for
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accessing values earlier in this course,
that would look like this.
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Let's save and run again.
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Okay, that gives us each of the values,
but
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there's a more Pythonic way to do this.
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There is a Python method called items
that can be used on dictionaries.
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And items returns a list of tuples,
where each tuple contains both the key and
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the value for
every item in the dictionary.
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And let's look at just that.
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I'm gonna come back to my code editor and
comment this out for a second.
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And we're gonna look at course.items.
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Take a look at each
tuple inside this list.
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The first element in each
tuple is the item's key, and
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the second is the item's value.
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So what this means is that we can use
the items method to loop over a list of
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tuples representing
the dictionaries's keys and
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value instead of iterating
directly over the dictionary.
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So let's erase this print statement.
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Uncomment our code here, and then I'm
gonna change course to course.items.
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And I will tell this to print item again.
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Now if we run this, it will print
out each tuple inside course.items.
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But to take this a step further,
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think back to what you might know about
unpacking tuples and multiple assignment.
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Tuples can be unpacked
into different variables,
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where each element of the tuple
is assigned to its own variable.
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This is handy in loops.
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If we change item in our for loop to
a tuple, like key, value, for instance,
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we can extrapolate the data in each
tuple into its own variable and
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use it within our loop.
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Let's take a look at what this looks like.
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Let's change a code here
to use multiple assignment.
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Now, the item variable in this code
will always reference the current tuple
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in the list that's returned
from course.items.
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If we replace item with key, value,
which is indeed another tuple,
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then we signal to the interpreter that
we want the first element in the current
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tuple to be assigned to key and the second
element to be assigned to value.
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Now we can access the key and
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the value of the current item in
the dictionary separate from one another.
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Let's try printing both of them and
then save and run.
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Cool, now we have our keys and
our values accessible inside the for
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loop in a clean Pythonic syntax.
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Congrats, join me in the next video to
learn about packing with dictionaries.
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