Copy vs View & Iterating

Some operations create a copy — a new array with its own data. Others create a view — a new array object that looks at the same data as the original.

• A copy owns its data: changing it never affects the original. • A view doesn't own its data: changing the view changes the original, and vice versa.

Views make NumPy fast and memory-efficient, because slicing a huge array doesn't duplicate it. But they can surprise you.