Dictionaries

Tutorial

A dictionary is a data type similar to arrays, but works with keys and values instead of indexes. Each value stored in a dictionary can be accessed using a key, which is any type of object (a string, a number, a list, etc.) instead of using its index to address it.

For example, a database of phone numbers could be stored using a dictionary like this:

phonebook = {}
phonebook["John"] = 938477566
phonebook["Jack"] = 938377264
phonebook["Jill"] = 947662781

Alternatively, a dictionary can be initialized with the same values in the following notation:

phonebook = {
    "John" : 938477566,
    "Jack" : 938377264,
    "Jill" : 947662781
}

Iterating over dictionaries

Dictionaries can be iterated over, just like a list. However, a dictionary, unlike a list, does not keep the order of the values stored in it. To iterate over key value pairs, use the following syntax:

for name, number in phonebook.iteritems():
    print "Phone number of %s is %d" % (name, number)

Removing a value

To remove a specified index, use either one of the following notations:

del phonebook["John"]

or:

phonebook.pop("John")

Exercise

Add "Jake" to the phonebook with the phone number 938273443, and remove Jill from the phonebook.

Tutorial Code

phonebook = {
    "John" : 938477566,
    "Jack" : 938377264,
    "Jill" : 947662781
}

# write your code here

# testing code
if "Jake" in phonebook:
    print "Jake is listed in the phonebook."
if "Jill" not in phonebook:
    print "Jill is not listed in the phonebook."

Expected Output

Jake is listed in the phonebook.
Jill is not listed in the phonebook.