When Passing Objects to Python Functions: Value or Reference?

Understanding Value Passing in Python

In Python, when passing a collection like a list or array to another function, the question arises whether a copy is made or if it remains a mere pointer. To address this, we delve into the intricacies of value passing in Python.

As per the Python documentation, references-to-objects are passed by value. This means that when a reference to an object is passed to a function, the value of the reference, not the object itself, is assigned to the variable inside the function.

However, Python's objects exhibit a distinction between mutability and immutability. Immutable objects, such as strings, tuples, and numbers, cannot be modified in-place within a function. If you attempt to alter them, a new instance of the object is created, leaving the original instance outside the function unchanged.

On the other hand, mutable objects like lists and dictionaries can be modified in-place. Therefore, any changes made to these objects within a function will also be reflected in the original object outside the function.

In summary, Python passes references-to-objects by value. However, the mutability of the object determines whether passing a reference behaves effectively like pass-by-value or pass-by-reference. Understanding this distinction is crucial for effective parameter passing in Python functions.

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