Answer to Question #171437 in Python for Paul Carpenter

Question

Create a Python dictionary that returns a list of values for each key. The key can be whatever type you want.

Design the dictionary so that it could be useful for something meaningful to you. Create at least three different items in it. Invent the dictionary yourself. Do not copy the design or items from some other source.

def invert_dict(d):

inverse = dict()

for key in d:

val = d[key]

if val not in inverse:

inverse[val] = [key]

else:

inverse[val].append(key)

return inverse

Modify this function so that it can invert your dictionary. In particular, the function will need to turn each of the list items into separate keys in the inverted dictionary.

Run your modified invert_dict function on your dictionary. Print the original dictionary and the inverted one.

Include your Python program and the output in your Learning Journal submission.

Describe what is useful about your dictionary. Then describe whether the inverted dictionary is useful or meaningful, and why.

Answer 1

def invert_dict(d):
    inverse = dict()
    for key in d:
        val = d[key]
        for item in val:
            if item not in inverse:
                inverse[item] = [key]
            else:
                inverse[item].append(key)
    return inverse


my_dict = {"London": ["Oxford Street", "Abbey Road", "Brick Lane", "Carnaby Street"],
           "New York": ["1st Ave.", "1st Ave Loop.", "1st Pl.", "2nd Ave."],
           "Berlin": ["Kaiserdamm", "Karl-Liebknecht-Strasse", "Karl-Marx-Allee", "Kopenhagener Strasse",
                       "Kurfürstendamm"]}

print('Original dictionary')
print(my_dict)
in_dict = invert_dict(my_dict)
print("Inverted dictionary")
print(in_dict)

The inverted dictionary is useful if one needs to find the city the exact street belongs to