Understanding Dictionaries in Python

Introduction to Dictionaries

• Dictionaries are one of four basic collection types in Python, alongside lists, sets, and tuples.
• Consist of key-value pairs.
• Ordered and changeable.
• No duplicate keys allowed.

Creating a Dictionary

• Syntax: dictionary_name = {}.
• Example - Dictionary of countries and capitals: capitals = { "USA": "Washington DC", "India": "New Delhi", "China": "Beijing", "Russia": "Moscow" }

Useful Functions

• dir(): Lists all attributes and methods of a dictionary.
  • Usage: dir(capitals).
• help(): Provides in-depth description of attributes and methods.

Accessing Values

• Use get() method to retrieve values:
  • Syntax: capitals.get("USA") returns "Washington DC".
  • If key is not found, returns None.
  • Example in an if statement: if capitals.get("Japan"): print("Capital exists") else: print("Capital doesn't exist")

Modifying Dictionaries

• Update dictionary: Use update() to add or change key-value pairs.
  • Add: capitals.update({"Germany": "Berlin"}).
  • Change existing: capitals.update({"USA": "Detroit"}).
• Remove entries:
  • pop(): Removes key-value pair by key.
    • Example: capitals.pop("China").
  • popitem(): Removes the last inserted key-value pair.
• Clear dictionary: clear() method removes all items.

Accessing Keys and Values

• Keys:
  • Use keys() method: keys = capitals.keys().
  • Iterable in a for loop: for key in capitals.keys(): print(key)
• Values:
  • Use values() method: values = capitals.values().
  • Iterable in a for loop: for value in capitals.values(): print(value)
• Items:
  • Use items() method: items = capitals.items().
  • Returns a view resembling a 2D list of tuples.
  • Iterable in a for loop: for key, value in capitals.items(): print(f"{key}: {value}")

Summary

• Dictionaries: Collection of key-value pairs.
• Ordered, changeable, no duplicates.
• Methods include get, update, pop, popitem, clear, keys, values, items.
• Useful for various programming tasks, including future game programming projects.