Numpy: Slicing is missing the stepping about adios HOT 4 OPEN

cc'ing @PrometheusPi, @ax3l

from adios.

Minimal "working" example, e.g. with the file from ax3l's issue #69

import adios as ad
f = ad.file("data_compressed.bp")
f["xy"][0, :6:2] == f["xy"][0, :3]

gives [True, True, True].

I think this should be considered a bug. The proper way of handling this should be raising a ValueError or a NotImplementedError (if it's possible that adios will support stepping at some time - which could be useful if you do not think about performance but the array does not fit into RAM - which was the case for Marco).
The current implementation masks the problem, since the shape of the returned array is as expected, so in the worst case a user just doesn't notice that he got the wrong data!

A fix in python (the wrapper is not written in python, is it? I will post some pseudocode anyway^^) would be:

def __getitem__(self, key):
    if isinstance(key, slice) and slice.step is not None:
        raise NotImplementedError
    return super().__getitem__(key)

from adios.

@n01r @ax3l @wmles we are currently supporting in ADIOS2 the Python low-level and high-level APIs. You can see then in action using Jupyter Notebooks running on MyBinder (see ReadMe): https://github.com/ornladios/ADIOS2-Jupyter

A few things about high-level APIs:

1. We don't have slicing/stride numpy syntax, high-level APIs are write/read based and are selection/random access (np_array = read("var", start, count, step_start, step_count)) and/or step-by-step based (using for step in stream). As in the spirit of Python we heavily overload these 2 functions, but read always returns a numpy array. For examples see:
   https://github.com/ornladios/ADIOS2/blob/master/testing/adios2/bindings/python/TestBPWriteTypesHighLevelAPI.py
2. We are maintaining these APIs and potentially adding more features. e.g. compression: https://github.com/ornladios/ADIOS2/blob/master/testing/adios2/bindings/python/TestBPZfpHighLevelAPI.py

Let me know if this is something of interest, ADIOS2 readers should be able to handle ADIOS1.x generated files. Thanks!

from adios.

You really do not want to stride during reads anyway for performance. Read all into a temporary var and stride in RAM :)

from adios.