Python Dictionary update() method

Python Dictionary update() method updates the dictionary with the elements from another dictionary object or from an iterable of key/value pairs.

# update() method in Dictionary

# Dictionary with three items
d1 = {'A': 'Geeks', 'B': 'For', }
d2 = {'B': 'Geeks', 'C': 'Python'}


# update the value of key 'B'
d1.update(d2)

# using keyword arguments
d1.update(A='Hello')

print(d1)

{'A': 'Hello', 'B': 'Geeks', 'C': 'Python'}

Syntax of Dictionary update Method

The dictionary update() method in Python has the following syntax:

Syntax: dict.update([other])

Parameters: This method takes either a dictionary or an iterable object of key/value pairs (generally tuples) as parameters.

Returns: It doesn't return any value but updates the Dictionary with elements from a dictionary object or an iterable object of key/value pairs.

Python Dictionary update() Example

Let us see a few examples of the update() method to update the data of the Python dictionary.

Update with another Dictionary

Here we are updating a dictionary in Python using the update() method and passing another dictionary to it as parameters. The second dictionary is used for the updated value.

# update() method in Dictionary

# Dictionary with three items
d1 = {'A': 'Geeks', 'B': 'For', }
d2 = {'B': 'Geeks', 'C': 'Python'}


# update the value of key 'B'
d1.update(d2)

print(d1)

{'A': 'Geeks', 'B': 'Geeks', 'C': 'Python'}

Update with Keyword Arguments

In this example, instead of using another dictionary, we passed an iterable value to the update() function.

# Dictionary with single item
d1 = {'A': 'Geeks'}

# update the Dictionary with iterable
d1.update(B='For', C='Geeks')
print(d1)

{'A': 'Geeks', 'B': 'For', 'C': 'Geeks'}

Python Dictionary Update Value if the Key Exists

In this example, we will update the value of a dictionary in Python if the particular key exists. If the key is not present in the dictionary, we will simply print that the key does not exist.

# Define dictionary
d = {'m': 700, 'n': 100, 't': 500}

# Key to check
key = 'm'

# Check if key exists and update
if key in d:
    print(f"Key exists. Value updated to 600.")
    d[key] = 600  # Directly update the value
else:
    print("Key does not exist.")

print(d)

Key exists. Value updated to 600.
{'m': 600, 'n': 100, 't': 500}

Python Dictionary Update Value if the Key doesn’t Exist

Here, we will try to update the value of the dictionary whose key does not exist in the dictionary. In this case, the key and value will be added as the new element in the dictionary.

# Define dictionary
d = {'m': 700, 'n': 100, 't': 500}

# Key to check
key = 'k'

# Check if key exists and update
if key not in d:
    print("Key doesn't exist. Adding a new key-value pair.")
    d[key] = 600  # Direct assignment
else:
    print("Key exists.")

# Print updated dictionary
print(d)

Key doesn't exist. Adding a new key-value pair.
{'m': 700, 'n': 100, 't': 500, 'k': 600}