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Dictionaries in Python

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Posted by Michael Sedique

A dictionary is a data type. In a way, it works similar to how an array would work, but it works a bit differently; they utilize keys and values rather than utilizing an index. To access a value in a dictionary, you use a key rather than index.

Example:

# phone book 
phonebook["Adam"] = 3108729066
phonebook["Mina"] = 9728891423
phonebook["Jasmine"] = 9491552251
phonebook["Zach"] = 4109246570
phonebook["Kendall"] = 6208291502
print(phonebook)

You can also set it up like this (I prefer this way):

# phone book 
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}
print(phonebook)

How about iterating over a dictionary

You can iterate dictionary over, similar to how you do with a list. Keep in mind, a dictionary is not like a list: a dictionary does not maintain the sequence of the values that are stored within it. In order to iterate over key value pairs, you can do this: 

# phone book 
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}
for name, number in phonebook.items():
    print("The phone number of %s is %d." % (name, number))

How do I remove a value?

In order to remove a specific index value, you can do this:

# phone book 
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}
del phonebook["Zach"] # sorry, Zach
print(phonebook)

You can also do this:

# phone book 
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}
phonebook.pop["Mina"] # sorry, Mina
print(phonebook)

Exercise

Let’s try to play with the phonebook concept. For this exercise, we can try to add a person with a phone number (you can pick the name and number). We also want to remove a person from the phonebook as well (again, you can pick as well). Please take a look at the solution if you get stuck!

Exercise:

# fill in your code here
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}

# testing code (adjust this based on who you select)

if "Jim" in phonebook and "Kendall" not in phonebook:
    print("Jake is listed in the phonebook.")
    print("Jill is no longer listed in the phonebook.")

Solution:

# fill in your code here
phonebook = {
    "Adam" : 3108729066,
    "Mina" : 9728891423,
    "Jasmine" : 9491552251,
    "Zach" : 4109246570,
    "Kendall" : 6208291502
}
phonebook["Jim"] = 9493102021
del phonebook["Adam"]

# testing code (adjust this based on who you select)

if "Jake" in phonebook and "Jill" not in phonebook:
    print("Jake is listed in the phonebook.")
    print("Jill is no longer listed in the phonebook.")

Output:

<script.py> output:
    Jim is listed in the phonebook.
    Kendall is no longer listed in the phonebook.

For more information

If you seek to learn more about Python, please visit Python’s official documentation.

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