Hi Tony,
Il giorno 09/lug/2013, alle ore 06:38, Tony Yu <tsy...@gmail.com> ha scritto:
> Hi,
>
> I ran into a subtle, unexpected issue while using `itertools.islice`. I
> wanted to pass slices of an array for processing without actually reading the
> entire array, and I wanted that processing function to know nothing about how
> I'm taking that slice. To that end, I had a loop that sliced the array using
> `itertools.islice` and called the function on each slice. Instead of
> returning the slice I specified, `islice` treated the previous end slice as
> the starting point to the next slice.
>
> That description is a bit confusing, but the example below (along with the
> attached test data) should illustrate the point. Maybe I'm missing something,
> but the only work around that I found was to set a private flag (e.g.
> `h5.root.array._init = False`) on each call to `islice` to reset the counter
> used in `__iter__`.
>
> I'm not sure if this is expected behavior or not, but it does differ from how
> `islice` works on numpy arrays (as demonstrated in the example below). I used
> the google and nothing similar came up, so I thought I'd post here.
>
> Best,
> -Tony
>
>
> #~~~~
>
> import tables
> import itertools
> import numpy as np
>
>
> h5 = tables.openFile('test.h5')
> array = np.arange(100)
> for i in range(5):
> # Numpy array slice always returns 0..10
> print list(itertools.islice(array, 0, 10))
> # PyTables array slice shifts with each iteration
> print list(itertools.islice(h5.root.array, 0, 10))
> h5.close()
> <test.h5>------------------------------------------------------------------------------
Yes, this is a bug IMO.
Thank you for reporting and thank you for the small demonstration script.
Can you please file a bug report on github [1]?
Please also add info about the PyTables version you used for the test..
[1] https://github.com/PyTables/PyTables/issues
--
Antonio Valentino
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