Chapter 4: Python Dictionaries and Sets

Introduction

• Dictionaries and Sets are important data structures in Python.
• Built-in data types frequently used in Python coding.
• Focus on special properties, methods, and practical applications.

Python Dictionaries

• Dictionary Concept: Works like a real-life dictionary with word-meaning pairs.
• Key-Value Pairs: Keys are like words, values are the meanings.
• Creation: Use curly braces {} with key-value pairs separated by colons.
• Example: { "name": "John", "age": 30 }.
• Data Types: Keys and values can be strings, integers, floats, booleans, lists, and tuples.
• Immutable Keys: Keys cannot be lists or dictionaries but can be strings, numbers, and tuples.
• Properties:
  • Unordered: No fixed order.
  • Mutable: Can change values.
  • No duplicate keys.

Accessing Dictionary Values

• Use key to access values: dictionary[key].
• dict.get(key) method avoids errors if the key is missing.
• Adding/Updating Values: Assign new values directly with dictionary[key] = value.
• Nested Dictionaries: Dictionary within a dictionary.

Dictionary Methods

• .keys(): Returns all keys as a list.
• .values(): Returns all values.
• .items(): Returns items as key-value tuples.
• .update(): Adds new key-value pairs.
• Checking Dictionary Type: type(dictionary) returns dict.

Python Sets

• Concept: Similar to mathematical sets with unique elements.
• Creation: Use curly braces {} or set() function.
• Properties:
  • Unordered: No indexing.
  • Unique and Immutable Elements.
• Adding/Removing Elements: .add() to add and .remove() to remove.
• Empty Set: Use set() function.

Set Methods

• .clear(): Empties the set.
• .pop(): Removes a random element.
• Union and Intersection:
  • union(): Combines unique elements from two sets.
  • intersection(): Finds common elements.

Practice Questions

1. Dictionary Word Meanings: Store pairs like "table": ["piece of furniture", "list of facts"].
2. Classroom Allocation: Use sets to find the number of unique classrooms needed.
3. Enter Marks: Store subject marks in a dictionary using user input.
4. Unique Set Values: Store 9 and 9.0 separately using strings or tuples for differentiation.

Conclusion

• Dictionaries and sets are versatile data structures in Python.
• Understanding their properties and methods is crucial for effective coding.
• Practice and application in further chapters will enhance comprehension.