Python update() Function

The update() function in Python is used when we need to update the value of specified key of a specified dictionary. If specified key is not available, then a new item with given key and value will get inserted. For example:

x = {"Day": "Sun", "Month": "Dec"}

x.update({"Day": "Mon"})
print(x)

x.update({"Year": "2021"})
print(x)

The output is:

{'Day': 'Mon', 'Month': 'Dec'}
{'Day': 'Mon', 'Month': 'Dec', 'Year': '2021'}

Python update() Function Syntax

The syntax of update() function in Python, is:

dictionary.update(iterable)

The iterable refers to a dictionary or an iterable of key-value pairs. The update() function does not returns any value. Therefore if you try to execute the following statement:

print(x.update({"Day": "Mon"}))

where x refers to a dictionary object, then the output will be None.

Python update() Function Example

Here is an example of update() function in Python. This program uses both dictionary and iterable (tuple) as iterable parameter while updating the dictionary:

x = {'Day': 'Sun'}
print(x)

a = {'Day': 'Mon', 'Date': '06'}
x.update(a)
print(x)

x.update(Month='Dec', Year='2021')
print(x)

The output is:

{'Day': 'Sun'}
{'Day': 'Mon', 'Date': '06'}
{'Day': 'Mon', 'Date': '06', 'Month': 'Dec', 'Year': '2021'}

Let's create the last example of update() function. This program allows user to define the size of dictionary along with its all items:

x = dict()
print("How many items to store in the dictionary: ", end="")
noOfItem = int(input())
print("\nEnter", noOfItem, "Items.")
for i in range(noOfItem):
    print("\nEnter the Key and Value for Item No.", i+1, ": ", sep="", end="")
    key = input()
    value = input()
    x.update({key: value})

print("\nThe dictionary is:")
print(x)

The snapshot given below shows the sample run, with user input 3 as number of items to insert in the dictionary, Name and Chloe as key and value of first item, Course and EECS as second item, University and MIT as third item:

Python Online Test