Python Dictionary copy() Method

The copy() method in Python is used to create a shallow copy of a dictionary. This method returns a new dictionary containing the same key-value pairs as the original dictionary. It is useful when you need to duplicate a dictionary and make changes to the copy without affecting the original dictionary.

Table of Contents

1. Introduction
2. copy() Method Syntax
3. Understanding copy()
4. Examples
   • Basic Usage
   • Modifying the Copied Dictionary
   • Copying a Nested Dictionary
5. Real-World Use Case
6. Conclusion

Introduction

The copy() method is a built-in dictionary method in Python that creates a shallow copy of a dictionary. This method is useful when you want to duplicate a dictionary and ensure that changes to the new dictionary do not affect the original dictionary.

copy() Method Syntax

The syntax for the copy() method is as follows:

dictionary.copy()

Parameters:

• The copy() method does not take any parameters.

Returns:

• A new dictionary that is a shallow copy of the original dictionary.

Understanding copy()

The copy() method creates a shallow copy of the dictionary, meaning that it copies the dictionary’s keys and values, but if any of the values are mutable objects (such as lists or other dictionaries), only the references to those objects are copied, not the objects themselves.

Examples

Basic Usage

To demonstrate the basic usage of copy(), we will create a copy of a dictionary and show that the original and the copy are independent.

Example

# Creating a dictionary with some key-value pairs
original_dict = {"a": 1, "b": 2, "c": 3}

# Creating a copy of the dictionary
copied_dict = original_dict.copy()

print("Original dictionary:", original_dict)
print("Copied dictionary:", copied_dict)

Output:

Original dictionary: {'a': 1, 'b': 2, 'c': 3}
Copied dictionary: {'a': 1, 'b': 2, 'c': 3}

Modifying the Copied Dictionary

This example shows that modifying the copied dictionary does not affect the original dictionary.

Example

# Creating a dictionary with some key-value pairs
original_dict = {"a": 1, "b": 2, "c": 3}

# Creating a copy of the dictionary
copied_dict = original_dict.copy()

# Modifying the copied dictionary
copied_dict["d"] = 4

print("Original dictionary after modification:", original_dict)
print("Copied dictionary after modification:", copied_dict)

Output:

Original dictionary after modification: {'a': 1, 'b': 2, 'c': 3}
Copied dictionary after modification: {'a': 1, 'b': 2, 'c': 3, 'd': 4}

Copying a Nested Dictionary

This example demonstrates copying a nested dictionary and highlights that the copy is shallow.

Example

# Creating a nested dictionary
original_dict = {"a": 1, "b": {"x": 10, "y": 20}}

# Creating a copy of the nested dictionary
copied_dict = original_dict.copy()

# Modifying the nested dictionary in the copy
copied_dict["b"]["z"] = 30

print("Original dictionary after modification:", original_dict)
print("Copied dictionary after modification:", copied_dict)

Output:

Original dictionary after modification: {'a': 1, 'b': {'x': 10, 'y': 20, 'z': 30}}
Copied dictionary after modification: {'a': 1, 'b': {'x': 10, 'y': 20, 'z': 30}}

Deep Copying a Dictionary

For cases where a deep copy is needed (i.e., copying the nested objects as well), use the copy module’s deepcopy function.

Example

import copy

# Creating a nested dictionary
original_dict = {"a": 1, "b": {"x": 10, "y": 20}}

# Creating a deep copy of the nested dictionary
deep_copied_dict = copy.deepcopy(original_dict)

# Modifying the nested dictionary in the deep copy
deep_copied_dict["b"]["z"] = 30

print("Original dictionary after deep copy modification:", original_dict)
print("Deep copied dictionary after modification:", deep_copied_dict)

Output:

Original dictionary after deep copy modification: {'a': 1, 'b': {'x': 10, 'y': 20}}
Deep copied dictionary after modification: {'a': 1, 'b': {'x': 10, 'y': 20, 'z': 30}}

Real-World Use Case

Backing Up Configuration Settings

In real-world applications, the copy() method can be used to create a backup of configuration settings stored in a dictionary before making changes.

Example

# Dictionary of configuration settings
config_settings = {
    "theme": "dark",
    "language": "English",
    "timeout": 30
}

# Creating a backup of the configuration settings
backup_settings = config_settings.copy()

# Modifying the configuration settings
config_settings["theme"] = "light"
config_settings["timeout"] = 60

print("Original configuration settings:", config_settings)
print("Backup configuration settings:", backup_settings)

Output:

Original configuration settings: {'theme': 'light', 'language': 'English', 'timeout': 60}
Backup configuration settings: {'theme': 'dark', 'language': 'English', 'timeout': 30}

Conclusion

The copy() method in Python is used for creating a shallow copy of a dictionary. By using this method, you can duplicate dictionaries and make changes to the copy without affecting the original dictionary. This method is particularly helpful in scenarios such as backing up configuration settings, managing collections of key-value pairs, and handling dictionaries in your Python applications.