How to copy a dictionary in Python?

In this Python Tutorial, we will see how to copy a dictionary in Python using some examples. We will see some methods to copy a Python dictionary.

A dictionary in Python can store so many key-value pairs in a place. And copying the data manually can be time-taking.

Or sometimes, we do some changes in the original data but, after some time, we need previous data to be restored(that cannot be retained back). So, we should not change the original data, until we are sure. Here, comes the use of copying a Python dictionary.

For example, there is a tech company having four different departments in it. They store the number of employees working in different departments in the form of a Python dictionary every year. What they do is, take the last year’s data and make a copy of it, and then update the copied one with the updation required. and store it as the

 employee_2022 = {
     'Networking': 5,
     'Cyber security': 10,
     'Developer': 12,
     'Administration': 8
}

print('Numbers of employees working in 2022: \n', employee_2022)

employee_2023 = dict(employee_2022)
print('Numbers of employees working in 2023: \n', employee_2023)

employee_2023['Developer']: 14
print('updated employee data in 2023: \n', employee_2023)

As the output of this code:

Numbers of employees working in 2022: 
 {'Networking': 5, 'Cyber security': 10, 'Developer': 12, 'Administration': 8}
Numbers of employees working in 2023: 
 {'Networking': 5, 'Cyber security': 10, 'Developer': 12, 'Administration': 8}
updated employee data in 2023: 
 {'Networking': 5, 'Cyber security': 10, 'Developer': 14, 'Administration': 8}
Previous year(2022) employee data: 
 {'Networking': 5, 'Cyber security': 10, 'Developer': 12, 'Administration': 8}

we can easily see that no change occurred in the last year’s stored data in the Python dictionary. And we easily updated the data to be the new year data. And now, we have both years’ data.

Copy a dictionary in Python

There are six different methods to copy a Python dictionary. They are:

• Using dict() constructor
• Using the dictionary comprehension method
• Using for loop
• Using copy()
• Using deepcopy() from copy module
• Using = (Assignment) Operator

Let’s see them one by one.

Method-1: Coping a Python dictionary using the dict() constructor

As we know, the dict() constructor is used to create a dictionary in Python. Here, we will just give the original dictionary as an argument to the dict() constructor and will store the value in the copied dictionary.

In the following example: we have a detail of an e-commerce inventory. Where the ID of the products are keys and the quantities available in inventory are values.

Product_data = {
     '004592': 36,
     '004593': 58,
     '004516': 20,
     '004603': 17
}

print('The original inventory data are: \n', Product_data)

Copied_product_data = dict(Product_data)

print('The inventory data that gonna be copied is: \n', Copied_product_data)

The output is:

The original inventory data are: 
 {'004592': 36, '004593': 58, '004516': 20, '004603': 17}
The inventory data that gonna be copied is: 
 {'004592': 36, '004593': 58, '004516': 20, '004603': 17}

This way we can easily use dict() in Python to copy a Python dictionary.

Method-2: Coping a Python dictionary using the dictionary comprehension

In this method, we will be using dictionary comprehension to craft a copied dictionary using the items of the original dictionary.

In this example: we have a company, that had assigned some projects to their employees in groups. By the time they can change the projects assigned to the employees.

Project_assigned = {
     'salesforce': ['Samy', 'abby'],
     'SAP': ['dave', 'david'],
     'Python': ['Veronica', 'joey']
}

print('Assigned project names: \n', Project_assigned)

Working_project = {key: value for key, value
                   in Project_assigned.items()}

print('Working project names: \n', Working_project)

The output of the Python code:

Assigned project names: 
 {'salesforce': ['Samy', 'abby'], 'SAP': ['dave', 'david'], 'Python': ['Veronica', 'joey']}
Working project names: 
 {'salesforce': ['Samy', 'abby'], 'SAP': ['dave', 'david'], 'Python': ['Veronica', 'joey']}

The company has successfully copied the Python dictionary using dictionary comprehension.

Method-3: Coping a Python dictionary using for loop

For loop in Python is used to loop over a sequence. Here, we will loop over the original dictionary using for loop, and we will save all the copied elements in the copied dictionary.

In the example: We have details of racers’ in the USA in 2023 with racers’ names and the record held by them. By the time these records can change.

Racers = {
     'Lex Hilton': '3:58.70i*',
     'Jake Gebhardt': '3:59.18i*',
     'Camden Marshall': '3:59.30i'
}

print('The top racers are: \n', Racers)

Copy_racers_data = {}

for key, value in Racers.items():
     Copy_racers_data[key] = value

print('the copies data : \n', Copy_racers_data)

The Output of this code:

The top racers are: 
 {'Lex Hilton': '3:58.70i*', 'Jake Gebhardt': '3:59.18i*', 'Camden Marshall': '3:59.30i'}
the copies data : 
 {'Lex Hilton': '3:58.70i*', 'Jake Gebhardt': '3:59.18i*', 'Camden Marshall': '3:59.30i'}

This way we can use for loop to copy a dictionary in Python.

Method-4: Coping a Python dictionary using copy() method

The copy() method in Python creates a shallow copy of a dictionary. The copy() function takes no arguments. Here, we will use the copy() method to copy the elements from the original dictionary to another dictionary.

In the example, we have data from a library, and there is the name of the book issued and the person to whom the book has been issued.

Library_books_week01 = {
    'Invisible Man': 'Amy',
    'Beloved': 'Cabby',
    'To Kill a Mockingbird': 'Ian'
}

print('Library books assigned: \n', Library_books_week01)

week02 = Library_books_week01.copy()

print('copied data from library:\n', week02)

The output is:

Library books assigned: 
 {'Invisible Man': 'Amy', 'Beloved': 'Cabby', 'To Kill a Mockingbird': 'Ian'}
copied data from library:
 {'Invisible Man': 'Amy', 'Beloved': 'Cabby', 'To Kill a Mockingbird': 'Ian'}

Method-5: Coping a Python dictionary using deepcopy() from copy module

The deepcopy() method in Python is a member of the copy module. It returns a new dictionary with copied elements of the passed dictionary. It copies, all the elements of the given dictionary in a recursive manner.

In the given example, we have taken the data from a cycle race. the racers have been assigned their track number. But, after the race starts the cyclist can change their track if required. So, to keep the records we need to change the data as per required.

import copy

cycle_race = {
     'rake': 5,
     'dave': 1,
     'gia': 2
}

print('cyclist name with their track number: \n', cycle_race)

after_1_hour = copy.deepcopy(cycle_race)

print('cyclist after 1 hour:\n', after_1_hour)

The output of this block of code:

Library books assigned: 
 {'Invisible Man': 'Amy', 'Beloved': 'Cabby', 'To Kill a Mockingbird': 'Ian'}
copied data from library:
 {'Invisible Man': 'Amy', 'Beloved': 'Cabby', 'To Kill a Mockingbird': 'Ian'}

This way, we can use deepcopy() from copy module to copy a Python dictionary.

Method-6: Coping a Python dictionary using =(Assignment Operator )

Assignment Operators are used to assign values to variables irrespective of the type or class of the value, as Python is a dynamically typed Programming language.

Until now, we saw the methods when we were changing or updating the data in the copied dictionary, and nothing happens to the original dictionary. But, In this method, if we change/update the copied dictionary data, automatically, the data will change in the original/parent dictionary.

To have a backup dictionary for any dictionary, we should use this method of copying a Python dictionary.

In this example, we will just use the = operator and will assign the original dictionary to a variable. Here, we have assigned the household work to the people. we will see how to copy this data and we will also see what happens to the original/parent Python dictionary when we change the data of copied dictionary.

work_assigned = {
     'Dusting': ['Samy', 'Abby'],
     'Cooking': ['Dave', 'David'],
     'Gardening': ['Veronica', 'Joey']
}

print('work assigned: \n', work_assigned)

work_going = work_assigned
print('Work going on: \n', work_going)

work_going['washing'] = ['Ian', 'Ray']
print('Updated work going on: \n', work_going)

print('Parent dictionary: \n', work_assigned)

The output of this block of code:

work assigned: 
 {'Dusting': ['Samy', 'Abby'], 'Cooking': ['Dave', 'David'], 'Gardening': ['Veronica', 'Joey']}
Work going on: 
 {'Dusting': ['Samy', 'Abby'], 'Cooking': ['Dave', 'David'], 'Gardening': ['Veronica', 'Joey']}
Updated work going on: 
 {'Dusting': ['Samy', 'Abby'], 'Cooking': ['Dave', 'David'], 'Gardening': ['Veronica', 'Joey'], 'washing': ['Ian', 'Ray']}
Parent dictionary: 
 {'Dusting': ['Samy', 'Abby'], 'Cooking': ['Dave', 'David'], 'Gardening': ['Veronica', 'Joey'], 'washing': ['Ian', 'Ray']}

This way, we can use the = operator to copy the dictionary in Python.

Conclusion:

This tutorial has seen many methods to copy a Python dictionary. If we want an actual copy, then we must want the copy not to affect the original dictionary, but if we want a copied dictionary to change should be backup data for the parent dictionary, kindly use the = operator function.

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