Understanding Dictionaries in Python

Introduction to Dictionaries

• A dictionary is one of the four basic collection types in Python.
• Consists of key-value pairs.
• Characteristics:
  • Ordered and changeable.
  • No duplicates allowed.

Creating a Dictionary

• Example: Dictionary of countries and capitals.
• Syntax: capitals = {} using curly braces.
• Adding entries using key-value pairs:
  • Example: "USA": "Washington DC"
  • Entries are separated by commas.
• Example entries:
  • USA: Washington DC
  • India: New Delhi
  • China: Beijing
  • Russia: Moscow

Dictionary Methods

Viewing Attributes and Methods

• Use dir(dictionary_name) to see all attributes and methods.
• Use help(dictionary_name) for detailed descriptions.

Accessing Values

• Use get method: dictionary_name.get(key).
• Example: capitals.get("USA") returns "Washington DC".
• If the key doesn't exist, returns None.

Checking for Key Existence

• Example: Check if a capital exists using an if statement.
  • if capitals.get("Japan"): print("Exists") else: print("Doesn't exist")

Updating a Dictionary

• Use update method to add or update key-value pairs.
• Example: capitals.update({"Germany": "Berlin"}).
• Updating an existing key:
  • Example: capitals.update({"USA": "Detroit"}).

Removing Entries

• Use pop to remove a specific key-value pair.
  • Example: capitals.pop("China").
• Use popitem to remove the last inserted key-value pair.
• Use clear to remove all entries from the dictionary.

Retrieving Keys and Values

Getting All Keys

• Use keys method: dictionary_name.keys().
• Returns an iterable object resembling a list.
• Can be used in a loop to iterate over all keys.

Getting All Values

• Use values method: dictionary_name.values().
• Returns an iterable object resembling a list.
• Can be used in a loop to iterate over all values.

Getting Key-Value Pairs

• Use items method: dictionary_name.items().
• Returns a dictionary object resembling a 2D list of tuples.
• Can be used in a loop to iterate over key-value pairs.

Conclusion

• Dictionaries are a flexible and powerful data structure in Python.
• Essential methods include get, update, pop, popitem, clear, keys, values, items.
• Useful for various applications, including future programming projects.