When Passing Objects, Does Python Pass Their Copies or References?

Understanding Value Passing in Python

When passing values in Python, it's crucial to grasp the concept of value types and object references. Unlike languages that employ pass-by-value, Python utilizes pass-by-object-reference.

In Python, everything is an object, and object references are passed by value. What does that mean? When you pass an object like a list or array to another function, Python doesn't create a copy of the object itself; instead, it creates a new reference that points to the existing object.

This has implications for mutable and immutable objects. Immutable objects, such as strings, tuples, and numbers, cannot be modified in-place. If you try to alter them within a function, a new instance of the object will be created, leaving the original unchanged.

However, mutable objects like lists and dictionaries can be modified in-place. This means that any changes made to these objects within a function will also affect the original object outside the function, as both references point to the same object instance.

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