PythonDictionariesCore Dictionary Operations

Core Dictionary Operations

Once you’ve created a dictionary, you’ll need to interact with it. The core operations involve accessing, adding, updating, and removing key-value pairs. Mastering these patterns is essential for effectively using dictionaries in your programs.

1. Accessing Values

There are two primary ways to get a value associated with a key.

Bracket Notation: dictionary[key]

This is the most direct way to access a value. You provide the key inside square brackets.

Pyground

Create a user profile and access the user's name and role using bracket notation.

Expected Output:


Name: Nisha Singh
Role: Designer

Output:

💥
KeyError: If you use bracket notation to access a key that does not exist in the dictionary, Python will raise a KeyError. This can crash your program if not handled properly.


2. Adding and Updating Entries


You can add a new key-value pair or update an existing one using simple bracket assignment.


    

  • If the key does not exist, a new key-value pair is created.
    • 

  • If the key already exists, its value is updated.
    • 



Pyground
Start with a user profile containing an 'id'. Add an 'email' and 'active' status, then update the 'id'.
Expected Output:

Initial user: {'id': 11}
After adding keys: {'id': 11, 'email': 'user@example.com', 'active': True}
After updating id: {'id': 15, 'email': 'user@example.com', 'active': True}

Output:


3. Merging Dictionaries


You often need to combine two dictionaries. Python offers several ways to do this.


The Merge | Operator (Python 3.9+)
This modern syntax is clean and expressive. It creates a new dictionary containing the items from both.
Pyground
Merge a base configuration with an override configuration using the `|` operator.
Expected Output:
{'host': 'api.example.com', 'port': 443, 'protocol': 'https'}
Output:


⚠️
Key Precedence: In both merging methods, if a key exists in both dictionaries, the value from the right-hand dictionary (the one being merged in) will overwrite the value in the left-hand one.


4. Removing Entries


There are several ways to remove items from a dictionary, each with different behaviors.


del Keyword
del removes a key-value pair. It’s simple but will raise a KeyError if the key doesn’t exist.
user = {"name": "Riya", "plan": "pro", "id": 30}
del user["plan"]
print(user) # Output: {'name': 'Riya', 'id': 30}
# del user["plan"] # Would raise KeyError now
Building DictionariesDictionary Methods Reference