Python Dictionary copy() Function

The Dictionary copy() method returns the Shallow copy of the specified dictionary.

Syntax

my_dictionary.copy()

copy() Parameters

Python Dictionary copy() function does not take any parameters.

copy() Return Value

Python Dictionary copy() function returns the Shallow copy of the specified dictionary.

note

It does not modify the original dictionary.

Examples

Example 1: Copy a Dictionary with copy()

Consider this example in which:

• original_dict.copy() creates a shallow copy of original_dict.
• When the age key in copied_dict is modified, it does not affect original_dict because the values in the dictionaries are references to the same objects.

# create a dictionary
original_dict = {'name': 'Tom', 'age':  20}

# create a copy of the original_dict
copied_dict = original_dict.copy() 

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

# Modifying the copied dictionary
copied_dict['age'] =  25

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

output

Original Dictionary: {'name': 'Tom', 'age': 20}
Copied Dictionary: {'name': 'Tom', 'age': 20}
Original Dictionary after modification: {'name': 'Tom', 'age': 20}
Copied Dictionary after modification: {'name': 'Tom', 'age': 25}

Example 2: Shallow Copy of a Dictionary with Mutable Values

The copy() method creates a Shallow copy!

In the following example the values in original_dict are lists (which are mutable) and so modifying one of the lists in copied_dict also affects the corresponding list in original_dict.

original_dict = {'fruits': ['apple', 'banana'], 'vegetables': ['carrot', 'tomato']}
copied_dict = original_dict.copy()

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

# Modifying the copied dictionary
copied_dict['fruits'].append('orange')

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

output

Original Dictionary: {'fruits': ['apple', 'banana'], 'vegetables': ['carrot', 'tomato']}
Copied Dictionary: {'fruits': ['apple', 'banana'], 'vegetables': ['carrot', 'tomato']}
Original Dictionary after modification: {'fruits': ['apple', 'banana', 'orange'], 'vegetables': ['carrot', 'tomato']}
Copied Dictionary after modification: {'fruits': ['apple', 'banana', 'orange'], 'vegetables': ['carrot', 'tomato']}

copy() vs Assignment statement

• When the copy() method is used, a new dictionary is created which is filled with a copy of the references from the original dictionary.
• When the = operator is used, a new reference to the original dictionary is created.

For example, an assignment statement does not copy objects.

old_dict = {'name': 'Tom', 'age': 25}
new_dict = old_dict
new_dict['name'] = 'xx'
print(old_dict) # Output: {'age': 25, 'name': 'xx'}
print(new_dict) # Output: {'age': 25, 'name': 'xx'}

output

{'name': 'xx', 'age': 25}
{'name': 'xx', 'age': 25}

When you execute new_dict = old_dict, you don’t actually have two dictionaries. The assignment just makes the two variables point to the one dictionary in memory.

So, when you change new_dict, old_dict is also modified. If you want to change one copy without changing the other, use copy() method.

old_Dict = {'name': 'Tom', 'age': 25}
new_Dict = old_Dict.copy()
new_Dict['name'] = 'xx'
print(old_Dict) # Output: {'age': 25, 'name': 'Tom'}
print(new_Dict) # Output: {'age': 25, 'name': 'xx'}

output

{'name': 'Tom', 'age': 25}
{'name': 'xx', 'age': 25}

Equivalent Method: Dictionary Comprehension

An alternative way to copy a dictionary is using dictionary comprehension.

my_dictionary = {'name': 'Tom', 'age': 25}
new_dictionary = {k:v for k,v in my_dictionary.items()}
print(new_dictionary) # Output: {'age': 25, 'name': 'Tom'}

output

{'name': 'Tom', 'age': 25}