Comparison to None in Numpy 1.9

[olaurino]

Since the Numpy 1.9 upgrade, users have been reporting warning messages like the following:

FutureWarning: comparison to None will result in an elementwise object comparison in the future.

Generally speaking, it is good practice to do None checks with if var is None rather than if var == None because the equality check can be (at least in principle) overridden. Which is what some of the Numpy structures do or are going to do in the future.

The issue is usually easy to fix, but getting a list of these warnings is not easy. We did fix some of them in the past (see 61fbfcd) but more have been reported, in particular:

sherpa/astro/io/crates_backend.py:1224
sherpa/sim/sample.py:184
sherpa/astro/ui/utils.py:8763
sherpa/astro/ui/utils.py:8768

For what is worth, a workaround exists:

import warnings
warnings.filterwarnings('ignore', category=FutureWarning)