Python Update Dictionary Value by Key

A Dictionary in Python is an unordered 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 dictionaries are mutable, meaning you can modify them in place.

In this article, I have explained how to update the value of an existing Key Dictionary. You only need to reassign a new value to that key. Python dictionaries allow for this direct modification.

Python Update Dictionary Value by Key

Here, we are explaining methods that explain how to Update Dictionary Value by Key in Python those are following.

• Using The Square Brackets
• Using Update() Method
• Using a Conditional Statement
• Using Setdefault Method

Update Dictionary by Key Using The Square Brackets

In this example, I have created a dictionary student_info, and we updated the 'grade' key to the new value 'A' using the square bracket notation.

# Creating a student information dictionary
student_info = {'name': 'Geek', 'age': 21, 'grade': 'B'}

# Updating the 'grade' key with value 'A'
student_info['grade'] = 'A'

# Displaying the updated dictionary
print(student_info)

{'grade': 'A', 'age': 21, 'name': 'Geek'}

Update Dictionary by Key Using Update() Method

In this example, below code updates the 'grade' value in the student_info dictionary to 'A' using the update() Method and then its prints the updated dictionary.

# Sample dictionary
student_info = {'name': 'Geek', 'age': 21, 'grade': 'B'}

# Using the update method to update the value for 'key2'
student_info.update({'grade': 'A'})

# Printing the updated dictionary
print(student_info)

{'name': 'Geek', 'age': 21, 'grade': 'A'}

Update Dictionary by Key Using a Conditional Statement

In this example, below code checks if the key 'grade' is in the `student_info` dictionary and, if true, updates its value to 'A'; then, it prints the updated dictionary `student_info`we used for these conditional statement .

# Sample dictionary
student_info = {'name': 'Geek', 'age': 21, 'grade': 'B'}

# Updating the value for 'key2' using a conditional statement
if 'grade' in student_info:
    student_info['grade'] = 'A'

# Printing the updated dictionary
print(student_info)

Output :

{'name': 'Geek', 'age': 21, 'grade': 'A'}

Update Dictionary by Key Using Setdefault Method

In this example code uses the `setdefault()` method to update the 'grade' value to 'A' in the `student_info` dictionary if the key 'grade' is not already present, and then prints the updated dictionary.

# Sample dictionary
student_info = {'name': 'Geek', 'age': 21, 'grade': 'B'}

# Using setdefault to update the value for 'key2'
student_info.setdefault('grade', 'A')

# Printing the updated dictionary
print(student_info)

Output :

{'name': 'Geek', 'age': 21, 'grade': 'A'}

Note: In case, since the key 'grade' already exists, setdefault() does not update its value to 'A'. Instead, it leaves the value as 'B'. So, If you want to update the value of a key regardless of whether it exists or not, you should directly assign the new value to the key as shown above example 1 [Update Dictionary by Key Using The Square Brackets].