Python Dictionary update() Method -

Python dictionary update() method is used to update the dictionary using another dictionary or an iterable of key-value pairs(such as a tuple). If the key is already present in the dictionary, the update() method changes the existing key with the new value.

1. Quick Examples of Python Dictionary update()

If you are in a hurry, below are some quick examples of the Python dictionary update() method.


# Quick examples of python dictionary update()

# Example 1: Update the dictionary
Technology = {'course': 'python', 'fee':4000}
Technology.update({'duration':'45days'})

# Example 2: Update the existing key of the dictionary
Technology= {'course': 'python', 'fee': 4000, 'duration': '45days'}
Technology.update({'duration':'60 days'})

# Example 3: Update using key-value pair
Technology= {'course': 'python', 'fee': 4000,}
Technology.update([('duration','45days'),('tutor','Richard')])

2. Syntax of Dictionary update()

Following is the syntax of the Python dictionary update() method.


# syntax of the dictionary update() 
dict.update(iterable)

2.1 Parameters of Dictionary update()

Python dictionary update() allows one parameter.

Iterable:(optional) It is either dictionary or an iterable key-value pair.

2.2 Return Value of Dictionary update()

It returns None.

3. Usage of Python Dictionary update() Method

Using Python Dictionary update() method we can update the dictionary by using another dictionary or an iterable of key-value pairs(such as a tuple). If the key is already present, this method updates the existing key with the new value from iterable value.

3.1 Add New Element to the Dictionary

You are using the update() method to add a new key-value pair to the Technology dictionary. This code initializes a dictionary called Technology with keys 'course' and 'fee'. Then, the update() method is used to add a new key-value pair 'duration': '45days' to the dictionary. Finally, the updated dictionary is printed


# Using update() update the dictionary
Technology = {'course': 'python', 'fee':4000}
Technology.update({'duration':'45days'})
print("Updated Technology:\n",Technology)

Yields below output.

3.2 Update the Existing key of Dictionary

When key is already present in the dictionary update() method updates the existing key with key-value pair. Using the update() method to update the value of an existing key in the Technology dictionary.

This program initializes a dictionary called Technology with keys 'course', 'fee', and 'duration'. Then, the update() method is used to update the value associated with the key 'duration' from '45days' to '60 days'. Finally, the updated dictionary is printed.


# Update the existing key of the dictionary
Technology= {'course': 'python', 'fee': 4000, 'duration': '45days'}
Technology.update({'duration':'60 days'})
print("Updated Technology:\n",Technology)

# Output:
# Updated Technology:
#  {'course': 'python', 'fee': 4000, 'duration': '60 days'}

In this example duration key existed with the value 45 days, which has been updated with the value 65 days.

4. Using tuple as a Param

You can use the update() method to add multiple key-value pairs to the Technology dictionary by passing an iterable (a list of tuples).

This code initializes a dictionary called Technology with keys 'course' and 'fee'. Then, the update() method is used to add multiple key-value pairs (('duration','45days') and ('tutor','Richard')) from an iterable (a list of tuples) to the dictionary. Finally, the updated dictionary is printed.


# Update the dictionary by passing iterable of key-value pair
Technology= {'course': 'python', 'fee': 4000,}
Technology.update([('duration','45days'),('tutor','Richard')])
print("Updated Technology:\n",Technology)

# Outputs:
# Updated Technology:
#  {'course': 'python', 'fee': 4000, 'duration': '45days', 'tutor': 'Richard'}

From the above code, we have passed tuple as a param to Python dictionary update() method, this added new elements duration and tutor to the dictionary.

Frequently Asked Questions On Python Dictionary update() Method

What does the update() method do in Python dictionaries?

The update() method is used to update a dictionary with elements from another dictionary or an iterable (e.g., a list of tuples). It adds new key-value pairs to the dictionary or updates the values of existing keys.

How does the update() method handle existing keys?

If the key already exists in the dictionary, the update() method will update the value of that key with the value from the provided dictionary or iterable.

Can I use the update() method with an iterable other than a dictionary?

You can provide an iterable (e.g., a list of tuples) to the update() method, as long as the iterable contains key-value pairs. Each tuple in the iterable should represent a key-value pair.

Can I use the update() method to remove keys from a dictionary?

The update() method is used for adding or updating key-value pairs; it does not remove keys. If you want to remove a key from a dictionary, you should use the pop() method or the del statement.

Can I update a dictionary with the values from another dictionary and also provide default values for missing keys?

The update() method itself does not provide a way to set default values for missing keys. If you want to set default values, you may need to iterate through the items of the other dictionary manually and set default values for missing keys.

Does the update() method modify the original dictionary in-place?

The update() method modifies the original dictionary in-place. It doesn’t return a new dictionary; instead, it updates the calling dictionary with the elements from the provided dictionary or iterable.

Conclusion

In this article, I have explained the Python Dictionary update() method with examples. By using a dictionary or an iterable of key-value pairs(such as a tuple) to update the dictionary? I have also explained how to update the existing key with updated key-value pair.

Happy Learning !!

References

https://docs.python.org/3/tutorial/datastructures.html