Dictionary

 

Dictionary is a collection of related data pairs. For example, if we want to store the age of five users, we can store them in a dictionary.

The following topics are discussed below:

1. Declaring a dictionary

    a. The first method

    b. The second method

2. Accessing individual items in a dictionary

3. Modifying items in a dictionary

4. Declaring an empty dictionary

5. Adding items in a dictionary

6. Removing items in a dictionary

Declaring a dictionary

The first method

To declare a dictionary, we write dictionaryName = {dictionary key: data}, with the requirement that dictionary keys must be unique (within one dictionary). That is, you cannot declare a dictionary as myDictionary = {"Peter":38, "John":51, "Peter":13}. This is because "Peter" is used as the dictionary key twice.

Example:

userNameAndAge ={"Peter":38, "John":51, "Alex":13, "Alvin":"Not Available"}

The second method

We can also declare a dictionary using the dict() method. To declare the userNameAndAge dictionary above, we write

userNameAndAge = dict(Peter = 38, John = 51, Alex = 13, Alvin = "Not Available")

When we use this method to declare a dictionary, we use parentheses instead of curly braces and do not put quotation marks for the keys.

Accessing individual items in a dictionary

To access individual items in the dictionary, we use the dictionary key, which is the first value in the {dictionary key: data} pair. For example, to get John's age, we write userNameAndAge["John"]. We will get the value 51.

Modifying items in a dictionary

To modify items in a dictionary, we write dictionaryName[dictionary key of item to be modified] = new data. For example, to modify the "John":51 pair, we write userNameAndAge["John"] = 21. The dictionary now becomes userNameAndAge ={"Peter":38, "John":21, "Alex":13, "Alvin":"Not Available"}.

Declaring an empty dictionary

We can also declare a dictionary without assigning any initial values to it. We simply write dictionaryName = {}. This is an empty dictionary with no items in it.

Adding items in a dictionary

To add items in a dictionary, we write dictionaryName[dictionary key] = data. For example, if we want to add "Joe":40 to our dictionary, we write userNameAndAge["Joe"] = 40. The dictionary now becomes userNameAndAge ={"Peter":38, "John":51, "Alex":13, "Alvin":"Not Available", "Joe":40}.

Removing items in a dictionary

To remove items from a dictionary, we write del userNameAndAge["Alex"]. The dictionary now becomes userNameAndAge ={"Peter":38, "John":51, "Alvin":"Not Available", "Joe":40}.