Currently numpy arrays are either writable or unwritable, but unwritable arrays can still be changed through other copies. This means that when a numpy array is passed into an interface that requires immutability for safety reasons, a copy always has to be made.
One way around this would be to add a NPY_IMMUTABLE flag signifying that the contents of the array will never change through other copies. This flag would be in addition to the current NPY_WRITEABLE flag, so it would be fully backwards compatible. The flag would be propagated along slices and views. For example, a numpy array created from C code that guarantees immutability would have the flag set. If the array was passed back into a function that required an immutable array, the code could check the immutable flag and skip the copy. This behavior could also be used to implement safe copy-on-write semantics. Making this more generally useful would probably require additional flags to document whether a writeable copy of the array might exists (something like NPY_LEAKED) in order to avoid copies for newly created writeable arrays. Has the issue of immutability been considered before? It seems like a basic NPY_IMMUTABLE flag would be fairly easy to add without backwards compatibility issues, but the secondary features such as NPY_LEAKED would be more complicated. Thanks, Geoffrey _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
