views and copies

Sometimes, even after five years using NumPy, I have to go with my gut feeling to predict if an operation will trigger a copy in the underlying data. – NumPy developer

When NumPy returns an array, it may be the same array (a view) or a new one (a copy).

There’s nothing obvious to tell which you’re getting, but the difference can change how the code behaves. Returning a view is faster because there’s no copying step. But a view is the gift that keeps on giving – if either side changes a cell, it silently changes for both.

• `Are there functions guaranteed to return one or the other?`_
• `Is there a rule to figure out which one Function X will return?`_
• `Can I turn a view into a copy?`_
• `Can I turn a copy into a view?`_
• `When can I ignore the difference?`_
• `Is there a way for code to tell me which one I’ve gotten?`_
• `Are there slick uses for one or the other?`_
• `What’s the deal with Pandas’ SettingWithCopyWarning?`_
• `Where can I find a more detailed explanation?`_