✅ Lesson: Dictionaries in Python ( by prompt AI teaching assistant )

 

✅ Lesson: Dictionaries in Python

[introduction]

Welcome back! Today we’re learning about dictionaries, a powerful way to store and organize data using key–value pairs. By the end of this lesson, you’ll know how to create, access, modify, and loop through dictionaries.

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[concept_explanation]

A dictionary in Python is a collection of key–value pairs.
Instead of accessing items by position (like lists), you access them using keys, which makes dictionaries great for storing structured data.

Key facts:

• Dictionaries are created using curly braces {}

• Keys must be unique

• Values can be any data type

• Dictionaries are mutable (you can change them)

Why they're useful:

• Perfect for storing real-world data (e.g., a student record, settings, preferences).

• Let you look up information quickly using a key.

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[python_examples]

1. Creating a dictionary

person = {
    "name": "Alice",
    "age": 20,
    "city": "London"
}

2. Accessing values

print(person["name"])
print(person.get("age"))

3. Adding or modifying items

person["age"] = 21
person["hobby"] = "painting"

4. Removing items

person.pop("city")
del person["hobby"]

5. Looping through a dictionary

for key, value in person.items():
    print(key, ":", value)

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[analogy]

A dictionary is like a real dictionary:
You look up a word (key) to find its definition (value).

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[practice_task]

Create a dictionary that stores:

• Your name

• Your favorite color

• Your age

Then:

• Add a new key-value pair

• Change one of the values

• Print all keys and values using a loop

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[quiz]

1. What symbol do we use to create a dictionary?

2. True or False: Keys in a dictionary can be duplicated.

3. What will this print?

student = {"name": "Sam", "grade": "A"}
print(student["grade"])

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[common_mistakes]

• Using a key that doesn’t exist → raises a KeyError

• Forgetting quotes around string keys

• Confusing lists’ indexing with dictionary key access

• Assuming dictionaries maintain order (they do in modern Python, but don’t rely on it unnecessarily)

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[extra_notes]

• Dictionaries now preserve insertion order (Python 3.7+).

• You can nest dictionaries:

student = {
    "name": "Liam",
    "scores": {"math": 92, "science": 88}
}

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[encouragement]

Excellent! You’ve mastered the basics of dictionaries. Ready for the next topic?