Dictionaries

Dictionaries are a very useful data structure. They are similar to lists, but instead of being indexed by integeres they are indexed by keys which can be of any type as long as they are immutable. In a dictionary the keys are used to access values.

A typical example would be the following:



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d = {'Angela':  23746, 'Sofia': 2514, 'Luis': 3747, 'Diego': 61562}

In this example the keys are strings (corresponding to names) and the values are numbers.

We can acess now the values:



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d['Angela']



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d['Diego']



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d['Luis']



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d['Sofia']

Adding a new element in the dictionary is very simple



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d['Valeriano'] = 1234



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print(d)

deleting an item is also easy to do



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d.pop('Angela')



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print(d)

It is possible to gather all the keys



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list(d.keys())

and also gather all the values



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list(d.values())

It is also easy to test whether a key (or value) is in the dictionary



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'Miguel' in d.keys()



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'Luis' in d.keys()

Exercise 3.01

Create a dictionary with the integers 0 to 4 as keys and the vowels (a, e, i, o u) as values.



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Exercise 3.02

Use the following dictionary of dictionaries to create a new dictionary that has the same keys and the values correspond to the total number of hours used in all activities.



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activities = {
    'Monday': {'study':4, 'sleep':8, 'party':0},
    'Tuesday': {'study':8, 'sleep':4, 'party':0},
    'Wednesday': {'study':8, 'sleep':4, 'party':0},
    'Thursday': {'study':4, 'sleep':4, 'party':4},
    'Friday': {'study':1, 'sleep':4, 'party':8},
}



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