How to Merge Two Dictionaries in Python Quickly and Easily

You can merge two dictionaries in Python using the {**dict1, **dict2} syntax or the dict1 | dict2 operator (Python 3.9+). Both methods combine keys and values, with later keys overwriting earlier ones if duplicates exist.

Syntax

There are two common ways to merge dictionaries in Python:

• {**dict1, **dict2}: Unpacks both dictionaries into a new one.
• dict1 | dict2: Uses the merge operator available in Python 3.9 and later.

In both cases, if the same key exists in both dictionaries, the value from dict2 will overwrite the one from dict1.

python

merged_dict = {**dict1, **dict2}

# or in Python 3.9+
merged_dict = dict1 | dict2

Example

This example shows how to merge two dictionaries using both methods and prints the result.

python

dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

# Using unpacking
merged1 = {**dict1, **dict2}
print('Merged with unpacking:', merged1)

# Using | operator (Python 3.9+)
merged2 = dict1 | dict2
print('Merged with | operator:', merged2)

Output

Merged with unpacking: {'a': 1, 'b': 3, 'c': 4}
Merged with | operator: {'a': 1, 'b': 3, 'c': 4}

Common Pitfalls

Some common mistakes when merging dictionaries include:

• Using dict1.update(dict2) modifies dict1 in place instead of creating a new dictionary.
• Trying to merge with + operator, which is not supported for dictionaries.
• Using the | operator in Python versions earlier than 3.9 causes errors.

python

dict1 = {'x': 1}
dict2 = {'y': 2}

# Wrong: + operator not supported
# merged = dict1 + dict2  # This will cause a TypeError

# Right: create new dict with unpacking
merged = {**dict1, **dict2}
print(merged)

Output

{'x': 1, 'y': 2}

Quick Reference

Summary of dictionary merge methods:

Method	Description	Python Version	Modifies Original?
{**dict1, **dict2}	Unpack and merge into new dict	All modern versions	No
dict1 | dict2	Merge using operator	3.9+	No
dict1.update(dict2)	Update dict1 in place	All versions	Yes

Key Takeaways

Use {**dict1, **dict2} to merge dictionaries without changing originals.

The | operator merges dictionaries cleanly in Python 3.9 and later.

If keys overlap, values from the second dictionary overwrite the first.

Avoid using + operator for dictionaries; it causes errors.

dict1.update(dict2) changes dict1 instead of creating a new dictionary.