[Numpy-discussion] Question about np.savez

David Warde-Farley dwf@cs.toronto....
Tue Sep 1 19:36:38 CDT 2009

On 1-Sep-09, at 9:08 AM, Pauli Virtanen wrote:

> Tue, 01 Sep 2009 12:07:36 +0000, jorgesmbox-ml kirjoitti:
>> I know the documentation states that np.savez saves numpy arrays,  
>> so my
>> question relates to misusing it. Before reading the doc in detail,  
>> and
>> after reading about pickle and other options to make data  
>> persistent, I
>> passed np.savez a list of ndarrays. It didn't complain, but when I
>> loaded the data back, the list had been turned into an ndarray. Is  
>> this
>> behaviour expected? It did surprise me. Below  there is an example:
> [clip]
> It is expected. savez casts its input to arrays before saving.

If you actually want to save multiple arrays, you can use  
savez('fname', *[a,b,c]) and they will be accessible under the names  
arr_0, arr_1, etc. and a list of these names is in the 'files'  
attribute on the NpzFile object. To retrieve your list of arrays when  
you load, you can just do

mynewlist = [data[arrname] for arrname in data.files]


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