Why Does Modifying a Python Dictionary Copy Also Change the Original?

Understanding Dictionary Copying in Python

In Python, manipulating dictionaries can be confusing when it comes to copying their values. This article addresses a common issue encountered when modifying a copy of a dictionary only to discover that the original dictionary has also changed.

To understand this behavior, it's crucial to grasp that Python doesn't perform implicit object copying. When you assign dict2 = dict1, you are not creating a new dictionary object; you are merely creating another reference to the same existing dictionary. Any changes made to dict2 will therefore directly affect dict1 as they both reference the same underlying data structure.

To avoid this behavior and truly copy a dictionary, you must explicitly create a new dictionary object. Two methods can achieve this:

• Using dict(): The dict() constructor takes an existing dictionary as its argument and returns a new dictionary object with a copy of all the key-value pairs.

Example:

dict2 = dict(dict1)

• Using copy(): The copy() method of a dictionary creates a new dictionary object with a superficial copy of the original.

Example:

dict2 = dict1.copy()

By using these techniques, you can ensure that modifications made to dict2 will not affect the original dict1, allowing you to preserve the state of the original dictionary while manipulating its copied version.

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