Unordered Collection

In this lesson you will learn Dictionary and Set; the two data structures which are not considered a sequence.

Dictionaries

Dictionary is a set of key:value pairs in which the keys are unique. A pair of braces creates an empty dictionary: { }

Although in the latest implementation of Python, dictionary maintains the order of insert, it is considered an implementation detail and should not be relied upon as it may change in the future as per the official documentation.

Here is an example of dictionary with values:

country_codes = {
    "US": "United States",
    "UK": "United Kingdom",
    "CA": "Canada",
    "MX": "Mexico",
}

print(country_codes)

Sequences are indexed by range of numbers but dictionaries are indexed by keys. A key can be of any immutable type although using a string or a number is most common. Tuples can be used as keys as long as the elements of the tuples are immutable.

Here are some of common operations on Dictionaries

Getting the maximum key or value

You can get the largest key using the max function. This is straight forward. However if you want to get the key which holds the highest value then you would use the below expression

d1 = {"a": 1, "b": 5, "c": 10}
max(d1, key=d1.get)

Output:
'c'

Hands-on Exercises

Exercise 1: Update Employee Profile

Create a dictionary representing an employee's profile: employee = {"id": 101, "name": "Sarah", "department": "Sales", "salary": 55000}

Write a Python program to:

1. Initialize the dictionary.
2. Update the salary key to 62000.
3. Add a new key-value pair: "status": "Active".
4. Delete the "department" key using the del keyword.
5. Print the final dictionary.

# Write your code below and click Run Code

employee = {"id": 101, "name": "Sarah", "department": "Sales", "salary": 55000}

# Update salary
employee["salary"] = 62000

# Add key-value
employee["status"] = "Active"

# Delete key
del employee["department"]

print("Updated profile:", employee)
# Output: {'id': 101, 'name': 'Sarah', 'salary': 62000, 'status': 'Active'}

Exercise 2: Top Earner Lookup

You have a dictionary that maps employee names to their monthly sales commissions: commissions = {"John": 1200, "Alice": 4500, "Bob": 3200, "Diana": 4100}

Write a Python program to:

1. Initialize the dictionary.
2. Find the name of the employee who earned the highest commission using the max() function with the custom key parameter key=commissions.get.
3. Print the top earner's name.

# Write your code below and click Run Code

commissions = {"John": 1200, "Alice": 4500, "Bob": 3200, "Diana": 4100}

# Find key with the highest value
top_earner = max(commissions, key=commissions.get)

print("Top earner is:", top_earner)
# Output: Top earner is: Alice