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Dictionaries

🟨🐍 Technique Card: Dictionaries in Python (practical)

Skill: Using dictionaries to store and look up information
Good for: Storing pairs of data like names and scores, words and meanings, country and capital, etc.

🧠 What’s a Dictionary in Python?

A dictionary is like a mini reference book or a box of labelled drawers.
You use a key to look up a value like in a real dictionary you use a word to look up a meaning.

# Example: animal sounds
animal_sounds = {
    "cat": "meow",
    "dog": "woof",
    "cow": "moo"
}

print(animal_sounds["dog"])  # Output: woof

💡 Common Use Cases for Dictionaries

Use Case Description
Storing settings or options For example, keeping a user’s preferences for a game ({"volume": 70, "difficulty": "easy"})
Counting things Like how many times each word appears in a sentence
Matching things Country to capital, word to translation, username to password
Lookup tables Fast way to get values using keys (e.g., Morse code translator)
Storing scores Player names and their scores in a game
Representing data from CSV files Each row of data as a dictionary with column names as keys

🧪 Try it Yourself

# Create a dictionary of favourite colours
favourite_colours = {
    "Alice": "blue",
    "Bob": "green",
    "Charlie": "red"
}

# Print Bob's favourite colour
print(favourite_colours["Bob"])

🧱 Key Techniques

Task How to do it
Create a dictionary my_dict = {"key": "value"}
Get a value my_dict["key"]
Add a new pair my_dict["new_key"] = "new_value"
Change a value my_dict["key"] = "new_value"
Loop through dictionary for key in my_dict:
print(key, my_dict[key])

Note

The values in a Python dictionary can be any datatype such as strings or integers or even lists and a dictionary can mix the datatypes of the values but the keys can only be strings or integers or floats or tuples

🎯 Practice Challenges

  1. Pet Sounds Dictionary
    Create a dictionary of animals and the sounds they make. Ask the user to type in an animal and print the sound.

  2. Top Scores
    Make a dictionary of names and scores. Print out each player’s name and score.

  3. Mini Translator
    Create a simple English to French dictionary. Ask the user for a word and show the translation.

🛠️ Useful Concepts

  • A dictionary is faster than a list to retrieve data (it doesn’t matter much in small projects but when working with large amounts of data it begins to make a difference).
  • Keys must be unique.
  • You can’t use a list as a key, but you can use strings or numbers.

🔗 Linked Cards

Watch the video