Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

Accessing Dictionary Information

All data stored within a dictionary is accessed via the key associated with the value you’re trying to access. We simply write the name of the dictionary followed by square brackets. Inside of the square brackets is the key. This will retrieve the value stored at that key:

# accessing dictionary information through keys person = { "name": 'John" } print( person[ "name" ] ) # access information through the key

Go ahead and run the cell. This will output “John” since that is what’s stored at the “name” key.

Using the Get Method

Another way of retrieving information is to use the get() method. The major difference between using this method and the previous way of accessing a value is that the get method won’t throw a key error. If the key doesn’t exist, it will simply return “None”. You may also add in a second argument in the call, in order to have the program return a more specific data type. Let’s try:

# using the get method to access dictionary information person = { "name": 'John" } print( person.get("name") ) # retrieves value of name key as before print( person.get("age", "Age is not available.") ) # get is a secure way to retrieve information

Go ahead and run the cell. On the second print statement, we’ll receive the “Age is not available” message because the key “age” does not exist. This gives us a more secure way of retrieving information.

Dictionaries with Lists

Dictionaries become powerful when you start working with data collections as values:

# storing a list within a dictionary and accessing it
data = { "sports": [ "baseball", "football", "hockey", "soccer" ] } print( data["sports"][0] ) # first access the key, then the index

Go ahead and run the cell. In order to access the list, we must first access the “sports” key. After that we can access items like any other list via the index. This will output “baseball”. Keep in mind that we cannot create a dictionary that stores a list without first attaching a key:

# improperly storing a list within a dictionary sports = [ "baseball", "football", "hockey", "soccer" ] sports_dict = dict( sports ) # will produce error, no key

Go ahead and run the cell. This will produce an error because there is no key associated with the sports variable. To properly store this list, you would write the following:
>>> sports_dict = dict( { "sports" : sports } )