Updating Python Dictionaries: Comparing Methods and Performance

In Python, a common task is updating dictionaries with user inputs. Let's consider a scenario where we have a default profile dictionary, and we want to update this dictionary based on user input.

profile = {'name': 'N/A', 'email': 'N/A', 'phone': 'N/A'}
user_input = {'name': 'Hayden', 'phone': '123-456-7890'}

# Notice: The user didn't input an email

Here, we have a default profile set up with 'N/A' values, and a user has provided their name and phone number. Now, how do we update our profile dictionary?

1. Using the update() function:


The update() method takes a dictionary as an argument and updates the original dictionary with the keys and values of the argument dictionary. If the key exists, it updates the value; otherwise, it adds the new key-value pair.

2. Using dictionary unpacking (**):

profile = {**profile, **user_input}

The double asterisks (**) operator unpacks the key-value pairs from the dictionaries and creates a new dictionary. If a key appears in both dictionaries, the value from the second dictionary (user_input here) is used.

3. Using the union operator (|=):

profile |= user_input

In Python 3.9 and later, we have a new operator for merging dictionaries: | and |= (union and in-place union operators). It works similarly to the update() function and ** operator, but slightly faster.

All three methods produce the same output, but the |= operator offers a small performance advantage. It's a neat trick to have up your sleeve, especially when working with larger dictionaries or where speed is crucial.

In conclusion, whether you're handling user profiles or any other form of dictionary data in Python, understanding these different methods of updating dictionaries will enable you to write more efficient and clean code.