Learn about Dictionaries datatype for Python

Lesson: Mastering Python Dictionaries – Learn about Dictionaries datatype for Python

Introduction to Python Dictionaries

A dictionary in Python is a collection of key-value pairs. Each key is unique and is used to access the corresponding value. Dictionaries provide an efficient way to store and retrieve data, where values can be any data type, but keys must be immutable types like strings, numbers, or tuples.

Creating a Dictionary

Method 1: Adding Entries Individually

phonebook = {}
phonebook["John"] = 555477566
phonebook["Jack"] = 555377264
phonebook["Jill"] = 555662781
print(phonebook)

Output:

{'John': 555477566, 'Jack': 555377264, 'Jill': 555662781}

Method 2: Initializing with Values

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

Output:

{'John': 938477566, 'Jack': 938377264, 'Jill': 947662781}

Accessing Values in a Dictionary

john_number = phonebook["John"]
print(john_number)

Output:

938477566

Modifying Values

phonebook["John"] = 555123456
print(phonebook)

Output:

{'John': 555123456, 'Jack': 938377264, 'Jill': 947662781}

Iterating Over Dictionaries

Dictionaries can be iterated over in various ways:

Iterating Over Keys

for name in phonebook:
    print(name)

Output:

John
Jack
Jill

Iterating Over Values

for number in phonebook.values():
    print(number)

Output:

555123456
938377264
947662781

Iterating Over Key-Value Pairs

for name, number in phonebook.items():
    print(f"Phone number of {name} is {number}")

Output:

Phone number of John is 555123456
Phone number of Jack is 938377264
Phone number of Jill is 947662781

Removing Entries

You can remove a specific key-value pair using the del statement or the .pop() method:

Using del Statement

del phonebook["John"]
print(phonebook)

Output:

{'Jack': 938377264, 'Jill': 947662781}

Using .pop() Method

phonebook.pop("John")
print(phonebook)

Output:

{'Jack': 938377264, 'Jill': 947662781}

Exercise

Task

1. Add “Jake” to the phonebook with the phone number 938273443.

2. Remove “Jill” from the phonebook.

Instructions

1. Create a dictionary phonebook with the initial values.
2. Add “Jake” to the dictionary.
3. Remove “Jill” from the dictionary.
4. Print the updated dictionary.
5. Verify the changes.

Sample Assignment

Initial Code

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

# 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.")

Solution

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

# Adding Jake and removing Jill
phonebook["Jake"] = 938273443
del phonebook["Jill"]

# 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.

Additional Concepts – Learn about Dictionaries datatype for Python

Nested Dictionaries

Dictionaries can contain other dictionaries, creating a nested structure:

contacts = {
    "John": {"phone": 938477566, "email": "john@example.com"},
    "Jack": {"phone": 938377264, "email": "jack@example.com"}
}
print(contacts)

Dictionary Comprehensions

Similar to list comprehensions, you can create dictionaries using dictionary comprehensions:

squares = {x: x*x for x in range(6)}
print(squares)

Output:

Additional Resources

• Comparing Python to Other Languages
• Learn RE – Regular Expressions in Python
• Python Serialization (JSON)
• Exception Handling in Python Programming
• Learn Python Lists
• Learn About Python Generators

Tools

You can use the Trinket.io online Python compiler to practice and run the code provided in this lesson.

Conclusion

Understanding dictionaries is essential for efficient data manipulation in Python. This lesson covered the basics and some advanced features of creating, modifying, iterating over, and deleting entries in dictionaries. Practice the exercises and explore the additional resources to deepen your understanding.