Python: update() method of dictionary

Rahul S
2 min readApr 16, 2023
src: datascience dojo

In Python, you can use the update() method to update a dictionary with key-value pairs from another dictionary or an iterable of key-value pairs. The syntax for using the update() method is as follows:

my_dict.update(other_dict)

or

my_dict.update(iterable)

Here, my_dict is the name of the dictionary that you want to update, other_dict is the dictionary from which you want to add key-value pairs, and iterable is an iterable of key-value pairs (e.g. a list of tuples).

When you call the update() method, any key-value pairs in other_dict or iterable that have keys that already exist in my_dict will overwrite the existing values. Any key-value pairs in other_dict or iterable that have keys that do not exist in my_dict will be added to my_dict.

Here’s an example:

# Define a dictionary
my_dict = {"apple": 2, "banana": 3, "orange": 4}

# Print the original dictionary
print("Original dictionary:", my_dict)

# Update the dictionary with key-value pairs from another dictionary
other_dict = {"banana": 5, "grape": 6}
my_dict.update(other_dict)

# Print the modified dictionary
print("Modified dictionary:", my_dict)

# Update the dictionary with key-value pairs from an iterable
iterable = [("kiwi", 2), ("banana", 7)]
my_dict.update(iterable)

# Print the modified dictionary again
print("Modified dictionary:", my_dict)

Output

Original dictionary: {'apple': 2, 'banana': 3, 'orange': 4}
Modified dictionary: {'apple': 2, 'banana': 5, 'orange': 4, 'grape': 6}
Modified dictionary: {'apple': 2, 'banana': 7, 'orange': 4, 'grape': 6, 'kiwi': 2}

Note that if you try to update a dictionary with an iterable that contains duplicate keys, only the last value for each key will be included in the resulting dictionary. This is because each key in a dictionary must be unique.

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