Dictionaries, Key-Value Pairs

Store data that needs to be looked up by name, not position

A dictionary stores key-value pairs, like a real dictionary where words are keys and definitions are values. You look things up by *key*, not by position.

How would you approach this? Think first, then expand.

Creating and using dictionariespython

person = {
    "name": "Alice",
    "age": 30,
    "city": "London"
}

print(person["name"])    # Alice
print(person.get("age")) # 30
person["email"] = "alice@example.com"  # Add new key
del person["city"]       # Remove a key

🔍Code TracerStep 1 / 7

trace.py

1person = {"name": "Alice", "age": 30}←

2person["city"] = "London"

3person["age"] = 31

4print(person)

Variables

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Looping through a dictionarypython

scores = {"Alice": 95, "Bob": 82, "Carol": 91}

for name, score in scores.items():
    print(f"{name}: {score}")

print(list(scores.keys()))    # ['Alice', 'Bob', 'Carol']
print(list(scores.values()))  # [95, 82, 91]

Dictionaries are perfect for counting. To count how often each item appears, use a dict where keys are items and values are counts. This is called the "frequency map" pattern.

🌍In the Real World...

Every JSON API response is a dictionary. Every Kubernetes manifest you parse is nested dictionaries. Terraform state files, Docker inspect output, AWS API responses, all dicts.

🎯

Phase Complete!

Data Structures

You know lists, tuples, dictionaries, and sets. For each one, name a real-world use case in DevOps or cloud engineering where that structure is the best choice.

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Practice Exercises

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Exercise 1 of 2medium

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Word Frequency

Write a function word_count(sentence) that returns a dictionary with the count of each word.
Example: word_count("the cat sat on the mat") → {"the": 2, "cat": 1, "sat": 1, "on": 1, "mat": 1}

solution.py

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Exercise 2 of 2medium

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Group by First Letter

Write a function group_by_first(words) that groups words by their first letter into a dictionary.
Example: group_by_first(["apple","avocado","banana","blueberry","cherry"])→ {"a": ["apple","avocado"], "b": ["banana","blueberry"], "c": ["cherry"]}

solution.py

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