[Numpy-discussion] Views of memmaps and offset

Gael Varoquaux gael.varoquaux at normalesup.org
Sat Sep 22 09:54:08 EDT 2012

Hi list,

I am struggling with offsets on the view of a memmaped array. Consider
the following:

import numpy as np

a = np.memmap('tmp.mmap', dtype=np.float64, shape=50, mode='w+')
a[:] = np.arange(50)
b = a[10:]

Here, I have a.offset == 0 and b.offset == 0. In practice, the data in b
is offset compared to the start of the file, given that it is a view
computed with an offset.

My goal is, given b, to find a way to open a new view on the file, e.g.
in a different process. For this I need the offset.

Any idea of how I can retrieve it? In the previous numpy versions, I
could go from b to a using the 'base' attribute of a. This is no longer

Also, should the above behavior be considered as a bug?



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