How does a shallow copy differ from a deep copy?

A shallow copy differs from a deep copy primarily in how it handles the objects it references. When a shallow copy is created, it duplicates just the references to the objects contained in the original object, rather than creating copies of those objects themselves. This means that if the original object contains references to mutable objects (such as lists or dictionaries), both the original and the shallow copy will refer to the same mutable objects. As a result, changes made to these mutable objects through one reference will be reflected in the other, as they point to the same underlying data.

In contrast, a deep copy creates a new object and recursively adds copies of nested objects found in the original, thus ensuring that the new object and the original one are completely independent. This distinction is crucial for memory management and data integrity, especially in complex applications where data may be modified in different parts of a program.

The other choices misrepresent the characteristics of shallow and deep copies, either by incorrectly describing the nature of the copying process or making assertions about performance that aren't inherently accurate. Understanding this difference is vital for effective programming, particularly when managing mutable data structures.