Lessons

Python Basics

Python Variables

Operators in Python

Conditional Statements in Python

Python Lists

Python Tuples

Python Sets

Python Dictionaries

Loops in Python

Python Arrays and Functions

Conclusion

Python Copy Dictionary

Copy Dictionaries in Python

In Python, dictionaries are mutable data structures that store data in key-value pairs. Sometimes, you may want to create a copy of a dictionary without linking it to the original. This lesson will guide you on how to copy dictionaries effectively in Python using different methods, ensuring that the copied dictionary is independent of the original.

1. Why Copy a Dictionary?

When you copy a dictionary, it is important to understand that a direct assignment (e.g., dict2 = dict1) does not create a new copy of the dictionary. Instead, it creates a reference to the original dictionary. Any changes made to one will affect the other.

Example: Direct Assignment Creates a Reference

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# Creating a dictionary
original_dict = {
    "brand": "Tesla",
    "model": "Model 3",
    "year": 2022
}

# Creating a reference to the original dictionary
copied_dict = original_dict

# Modifying the copied dictionary
copied_dict["year"] = 2023

print(original_dict)  # Output: {'brand': 'Tesla', 'model': 'Model 3', 'year': 2023}

In this example, changing copied_dict also changes original_dict because both variables point to the same dictionary.

2. Copying a Dictionary Using the copy() Method

One of the simplest ways to create a copy of a dictionary is by using the built-in copy() method. This method creates a shallow copy of the dictionary.

Example: Copying with the copy() Method

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# Creating a dictionary
car_info = {
    "brand": "Audi",
    "model": "A4",
    "year": 2021
}

# Making a copy of the dictionary
car_copy = car_info.copy()

print(car_copy)  # Output: {'brand': 'Audi', 'model': 'A4', 'year': 2021}

3. Copying a Dictionary Using the dict() Function

Another method to copy a dictionary is by using the built-in dict() function. This approach also creates a shallow copy.

Example: Copying with the dict() Function

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# Creating a dictionary
laptop_info = {
    "brand": "HP",
    "model": "Pavilion",
    "year": 2020
}

# Making a copy of the dictionary using dict()
laptop_copy = dict(laptop_info)

print(laptop_copy)  # Output: {'brand': 'HP', 'model': 'Pavilion', 'year': 2020}

4. Deep Copying a Dictionary

For nested dictionaries, where you want to copy all levels of the dictionary, you will need to create a deep copy using the copy module's deepcopy() method. This ensures that all levels of the original dictionary are copied, rather than just creating references.

Example: Deep Copying a Nested Dictionary

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import copy

# Creating a nested dictionary
nested_dict = {
    "brand": "Apple",
    "products": {
        "phone": "iPhone",
        "laptop": "MacBook"
    }
}

# Making a deep copy of the nested dictionary
nested_copy = copy.deepcopy(nested_dict)

# Modifying the copy
nested_copy["products"]["phone"] = "iPhone 14"

print(nested_dict)  # Output: {'brand': 'Apple', 'products': {'phone': 'iPhone', 'laptop': 'MacBook'}}
print(nested_copy)  # Output: {'brand': 'Apple', 'products': {'phone': 'iPhone 14', 'laptop': 'MacBook'}}

In this example, modifying nested_copy does not affect nested_dict, demonstrating the advantage of deep copying for nested structures.

Frequently Asked Questions