🚀 Day 73/150 – Merge Two Dictionaries in Python

Dictionaries are one of Python’s most useful data structures, and combining two dictionaries is a common task when working with data.

In this post, we'll explore different ways to merge dictionaries in Python.

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✅ Method 1 – Using update()

The update() method adds all key-value pairs from one dictionary into another.

dict1 = {"name": "John", "age": 20}
dict2 = {"course": "Python", "city": "Delhi"}

dict1.update(dict2)

print(dict1)

Output

{'name': 'John', 'age': 20, 'course': 'Python', 'city': 'Delhi'}

How it works

• update() modifies the original dictionary.
• Existing keys are overwritten if duplicates exist.

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✅ Method 2 – Using Dictionary Unpacking (**)

Python allows unpacking dictionaries and combining them into a new dictionary.

dict1 = {"name": "John", "age": 20}
dict2 = {"course": "Python", "city": "Delhi"}

result = {**dict1, **dict2}

print(result)





Output

{'name': 'John', 'age': 20, 'course': 'Python', 'city': 'Delhi'}

Why use it?

• Creates a new dictionary.
• Keeps the original dictionaries unchanged.

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✅ Method 3 – Using the | Operator (Python 3.9+)

Python 3.9 introduced a dedicated merge operator for dictionaries.

dict1 = {"name": "John", "age": 20}
dict2 = {"course": "Python", "city": "Delhi"}

result = dict1 | dict2

print(result)

Output

{'name': 'John', 'age': 20, 'course': 'Python', 'city': 'Delhi'}

Benefits

• Clean and readable syntax.
• Returns a new merged dictionary.

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✅ Method 4 – User-Defined Dictionaries

You can merge any dictionaries created by the user.

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

merged = {**dict1, **dict2}

print(merged)





Output

{'a': 1, 'b': 2, 'c': 3, 'd': 4}

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⚠️ What Happens with Duplicate Keys?

dict1 = {"name": "John", "age": 20}
dict2 = {"age": 25, "city": "Delhi"}

result = {**dict1, **dict2}

print(result)

Output

{'name': 'John', 'age': 25, 'city': 'Delhi'}


The value from the second dictionary replaces the value from the first dictionary when keys are the same.

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🎯 Key Takeaways

✔️ Use update() when you want to modify the existing dictionary.
✔️ Use ** unpacking when you want a new merged dictionary.
✔️ Use | operator for cleaner syntax in Python 3.9+.
✔️ If duplicate keys exist, the last dictionary's value wins.