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.

Example:

Original dictionary : {'A': 'Geeks', 'B': 'For'}
Updated dictionary : {'A': 'Geeks', 'B': 'Geeks'}

Original dictionary : {'A': 'Geeks', 'B': 'For'}
Updated dictionary : {'A': 'Geeks', 'B': 'For', 'C': 'Geeks'}

Syntax of Python 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.

Python3

# Python program to show working
# of update() method in Dictionary

# Dictionary with three items
Dictionary1 = {'A': 'Geeks', 'B': 'For', }
Dictionary2 = {'B': 'Geeks'}

# Dictionary before Updation
print("Original Dictionary:")
print(Dictionary1)

# update the value of key 'B'
Dictionary1.update(Dictionary2)
print("Dictionary after updation:")
print(Dictionary1)

Output:

Original Dictionary:
{'A': 'Geeks', 'B': 'For'}
Dictionary after updation:
{'A': 'Geeks', 'B': 'Geeks'}

Update with an Iterable

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

Python3

# Python program to show working
# of update() method in Dictionary

# Dictionary with single item
Dictionary1 = {'A': 'Geeks'}

# Dictionary before Updation
print("Original Dictionary:")
print(Dictionary1)

# update the Dictionary with iterable
Dictionary1.update(B='For', C='Geeks')
print("Dictionary after updation:")
print(Dictionary1)

Output

Original Dictionary:
{'A': 'Geeks'}
Dictionary after updation:
{'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.

Python3

def checkKey(dict, key):

    if key in dict.keys():
        print("Key exist, ", end =" ")
        dict.update({'m':600})
        print("value updated =", 600)
    else:
        print("Not Exist")
dict = {'m': 700, 'n':100, 't':500}

key = 'm'
checkKey(dict, key)
print(dict)

Output:

Key exist,  value updated = 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.

Python3

def checkKey(dict, key):

    if key not in dict.keys():
        print("Key doesn't exist So, a new Key-Value pair will be created")
        dict.update({key:600})
    else:
        print("Key Exist")
dict = {'m': 700, 'n':100, 't':500}

key = 'k'
checkKey(dict, key)
print(dict)

Output:

Key doesn't exist So, a new Key-Value pair will be created
{'m': 700, 'n': 100, 't': 500, 'k': 600}