FAQ: Collections - DefaultDict

Frequently Asked Questions Uncategorized
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Community%20FAQs%20on%20Codecademy%20Exercises
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This community-built FAQ covers the “DefaultDict” exercise from the lesson “Collections”.

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This exercise can be found in the following Codecademy content:

Learn Intermediate Python 3

FAQs on the exercise DefaultDict

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2

Hi there.
It is not clear, why DefaultDict class should be used instead of simple method .get(key, defvalue)?

3

#get-help In the solution,

site_locations[item] = validated_locations[item]

is used. But I don’t understand why site_locations.update((item, validated_location[item])) does not work.

Could anyone please explain this?

Thank you

4

Firstly, there seems to be a typo (unless it is just a slip during copy/pasting in the forums). You wrote
validated_location[item] instead of validated_locations[item].

Other than that, have a look at the documentation for update,

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scrn1778×154 8.07 KB

In your attempted solution,

site_locations.update((item, validated_locations[item]))

the outer pair of parentheses belong to the update method, while the inner pair of parentheses belong to the iterable(tuple). But, the documentation mentions “… or an iterable of key/value pairs (as tuples or other iterables of length two)…”

The elements of your iterable(tuple) are not key/value pairs or other iterables which can be interpreted as being key/value pairs.

Here are some variations which should work,


site_locations.update([(item, validated_locations[item])]) 
# The iterable is a list with a single element.
# That element is a tuple/iterable of length 2.

site_locations.update(((item, validated_locations[item]),)) 
# The iterable is a tuple with a single element.
# That element is a tuple/iterable of length 2.
# The comma has been used because there is only one element in the outer tuple and
# we want the parentheses to be interpreted as belonging to a tuple.
# e.g. 
# Single element with parentheses
x = (3)
print(type(x)) # <class 'int'>

x = (3,)
print(type(x)) # <class 'tuple'>

# No need for trailing comma if more than one element is inside parentheses.
# No ambiguity in the parentheses being interpreted as a tuple.
x = (3, 4)
print(type(x)) # <class 'tuple'>

You can also have multiple tuples/iterables of length 2 inside the iterable e.g.

x = {'a': 1, 'b': 2, 'c': 3}

x.update([("a", 3), ("b", 100), ["z", 88]])
# Iterable is a list whose elements are iterables of length 2

print(x)  
# {'a': 3, 'b': 100, 'c': 3, 'z': 88}

# This will also work
x.update((("a", 3), ("b", 100), ["z", 88]))
# Iterable is a tuple whose elements are iterables of length 2
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