Check and Update Existing Key in Python Dictionary

A dictionary in Python is an ordered collection of key-value pairs. Each key must be unique, and you can use various data types for both keys and values. Dictionaries are enclosed in curly braces {}, and the key-value pairs are separated by colons. Python Dictionary is mutable, meaning you can modify them in place.

In this article, I have explained the process of updating existing keys in a dictionary in Python. To update an existing key in a dictionary, you’ll need to create a new key with the updated name and the same value as the old key and then delete the old key.

Update Existing Key in Dictionary Python

Here, are various ways to Update Existing Key in Dictionary Python. Here we are discussing some generally used methods to Update Existing key values key-value in Dictionary Python those are following.

Update Existing Key using Direct Assignment

In this example, the below code updates the dictionary by renaming the key ‘rank’ to ‘age’ while presenting the original value, and then removes the old key ‘rank’ and the updated dictionary is printed.

Python3

# Initial dictionary
user = {'name': 'Geek', 'rank': 10, 'city': 'Geek Town'}

# Update existing key using direct assignment
if 'rank' in user:
    user['age'] = user['rank']
    del user['rank']

# Print the updated dictionary
print(user)

Output:

{'name': 'Geek', 'city': 'Geek Town', 'age': 10}

Update Existing Key using pop Method

In this example, a ‘user’ dictionary with 3 key-value pairs {‘name’: ‘Geek’, ‘rank’: 10, ‘city’: ‘Geek Town’} are present and I have updated the key ‘city’ to ‘town’ without changing the value.

Python

# Creating a dictionary
user = {'name': 'Geek', 'rank': 10, 'city': 'Geek Town'}

# Updating the key name from 'city' to 'town' and keeping the same value
user['town'] = user.pop('city')

# Displaying the updated dictionary
print(user)

Output

{'town': 'Geek Town', 'name': 'Geek', 'rank': 10}

Check if a Key Exists in a Dictionary in Python

Using If Condition

In this example, we will first check if the old key ‘rank’ exists in the ‘user’ dictionary using the in operator. If it exists, we create a new key ‘age’ with the same value as the old key and then remove the old key using pop operation.

Python

# Initial dictionary
user = {'name': 'Geek', 'rank': 10, 'city': 'Geek Town'}

# Check if the old key exists before updating
if 'rank' in user:
    # Create a new key with the updated name and the same value
    user['age'] = user.pop('rank')

# Print the updated dictionary
print(user)

Output

{'city': 'Geek Town', 'age': 10, 'name': 'Geek'}

Using Try-Except Block

In this example , below code attempts to update the ‘age’ key in the dictionary by replacing the ‘rank’ key using the try-except block to handle the case where ‘rank’ key doesn’t exist.

Python3

# Initial dictionary
user = {'name': 'Geek', 'rank': 10, 'city': 'Geek Town'}

# Update existing key using try-except block
try:
    user['age'] = user.pop('rank')
except KeyError:
    pass  # Handle the case where the key doesn't exist

# Print the updated dictionary
print(user)

Output :

{'name': 'Geek', 'city': 'Geek Town', 'age': 10}