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.

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

Example #1: Update with another Dictionary

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'}

Example #2: Update with an iterable

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'}

Example #3: Python dictionary update value if the key exists

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}

Example #4: Python dictionary update value if the key doesn’t exists

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}

Note: A new Key value pair gets created automatically if given Key is not present in the Dictionary.