[Numpy-discussion] saving groups of numpy arrays to disk

David Warde-Farley wardefar@iro.umontreal...
Thu Aug 25 17:49:16 CDT 2011

On 2011-08-25, at 2:42 PM, Chris.Barker wrote:

> On 8/24/11 9:22 AM, Anthony Scopatz wrote:
>>    You can use Python pickling, if you do *not* have a requirement for:
> I can't recall why, but it seem pickling of numpy arrays has been 
> fragile and not very performant.
> I like the npy / npz format, built in to numpy, if you don't need:
>>    - access from non-Python programs

While I'm not aware of reader implementations for any other language, NPY is a dirt-simple and well-documented format designed by Robert Kern, and should be readable without too much trouble from any language that supports binary I/O. The full spec is at


It should be especially trivial to read arrays of simple scalar numeric dtypes, but reading compound dtypes is also doable.

For NPZ, use a standard zip file reading library to access individual files in the archive, which are in .npy format (or just unzip it by hand first -- it's a normal .zip file with a special extension).


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