11.4. Dictionaries and Tuples

Dictionaries have a method called items that returns a list of tuples, where each tuple is a key-value pair. (Technically, it returns a “view object,” but using it as the parameter in Python’s list() constructor converts it into a list.)

d = {'a':10, 'b':1, 'c':22} t = list(d.items()) print(t)

Before you keep reading...

Runestone Academy can only continue if we get support from individuals like you. As a student you are well aware of the high cost of textbooks. Our mission is to provide great books to you for free, but we ask that you consider a $10 donation, more if you can or less if $10 is a burden.

Support Runestone Academy Today

Before you keep reading...

Making great stuff takes time and $$. If you appreciate the book you are reading now and want to keep quality materials free for other students please consider a donation to Runestone Academy. We ask that you consider a $10 donation, but if you can give more thats great, if $10 is too much for your budget we would be happy with whatever you can afford as a show of support.

Support Runestone Academy Today

11-9-2: True or false? The following code will correctly output the items of the dictionary t.

name_dictionary = {'Bob': 5, 'Melissa': 3, 'John': 7, 'Kim': 5}
t = list(name_dictionary.items)
print(t)

• True
• Incorrect! Look closely at the second line. Notice anything missing? Try again.
• False
• Correct! Parentheses are required when calling the items() method.

As you should expect from a dictionary, the items are in no particular order. However, since a list of tuples is a list, and tuples are comparable, we can sort the list of tuples. Converting a dictionary to a list of tuples is a way for us to output the contents of a dictionary sorted by key:

d = {'b':1, 'a': 10, 'c':22} t = list(d.items()) print(t) #should print [('b', 1), ('a', 10), ('c', 22)] t.sort() print(t) #should print [('a', 10), ('b', 1), ('c', 22)]

(If you need a reminder, the sort method sorts a list in alphabetical order.)

The resulting list is sorted in ascending alphabetical order by the key value.

11-9-4: How will the list below be sorted (if there is any order at all)?

grocery_dict = {'apple': 5, 'pineapple': 3, 'chicken': 8, 'kiwi': 7}
grocery_list = list(grocery_dict.items())
grocery_list.sort()

• In ascending order by the keys' first letter.
• Correct! This is the way that the sort() method sorts lists of tuples.
• In descending order by each key's value.
• Incorrect! The sort() method doesn't consider the keys' values at all. Try again.
• In descending order by the keys' first letter.
• Incorrect! The default way that the sort() method sorts is in ascending order. Try again.
• In ascending order by each key's value.
• Incorrect! The sort() method doesn't consider the keys' values at all. Try again.

The sort method also has an optional parameter, reverse, whose value can tell sort to sort in descending order.

grocery_dict = {'apple': 5, 'pineapple': 3, 'chicken': 8, 'kiwi': 7} grocery_list = list(grocery_dict.items()) grocery_list.sort(reverse=True) print(grocery_list) #should print [('pineapple', 3), ('kiwi', 7), ('chicken', 8), ('apple', 5)]

Write code that will transform dictionary d into a list of tuples, called tup_list, sorted by the keys in descending order.

d = {'a': 10, 'b': 2, 'c': 27, 'd': 15, 'e': 30, 'f': 3} ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(tup_list, [('f', 3), ('e', 30), ('d', 15), ('c', 27), ('b', 2), ('a', 10)], "Checking to make sure the list was sorted correctly.") self.assertEqual(len(tup_list), 6, "Checking to make sure no values were added or deleted.") myTests().main()

You have attempted 1 of 7 activities on this page