How to Copy a Dictionary in Python: Simple Methods Explained

To copy a dictionary in Python, use the copy() method or the dict() constructor to create a shallow copy. For a deep copy that copies nested objects, use the copy.deepcopy() function from the copy module.

Syntax

There are two common ways to copy a dictionary in Python:

• Using copy() method: Creates a shallow copy of the dictionary.
• Using dict() constructor: Also creates a shallow copy by passing the original dictionary.

For deep copies (copying nested dictionaries), use copy.deepcopy() from the copy module.

python

new_dict = original_dict.copy()

# or

new_dict = dict(original_dict)

Example

This example shows how to copy a dictionary using copy() and how modifying the copy does not affect the original dictionary.

python

original = {'a': 1, 'b': 2}
copied = original.copy()
copied['a'] = 100
print('Original:', original)
print('Copied:', copied)

Output

Original: {'a': 1, 'b': 2}
Copied: {'a': 100, 'b': 2}

Common Pitfalls

A common mistake is expecting copy() or dict() to copy nested dictionaries deeply. They only create shallow copies, so changes to nested objects affect both dictionaries.

Use copy.deepcopy() to avoid this problem.

python

import copy

original = {'outer': {'inner': 1}}
shallow_copy = original.copy()
deep_copy = copy.deepcopy(original)

shallow_copy['outer']['inner'] = 100
print('Original after shallow copy change:', original)

deep_copy['outer']['inner'] = 200
print('Original after deep copy change:', original)

Output

Original after shallow copy change: {'outer': {'inner': 100}}
Original after deep copy change: {'outer': {'inner': 100}}

Quick Reference

Method	Description
copy()	Creates a shallow copy of the dictionary.
dict()	Creates a shallow copy by passing the original dictionary.
copy.deepcopy()	Creates a deep copy including nested objects.

Key Takeaways

Use copy() or dict() for a shallow copy of a dictionary.

Shallow copies do not copy nested objects; changes to nested data affect both dictionaries.

Use copy.deepcopy() to copy nested dictionaries safely.

Modifying the copied dictionary does not change the original if the copy is shallow and values are immutable.

Always import the copy module to use deepcopy().