cover cp.abs() using the builtin

[Dimosts]

To cover the case of cp.abs().

Currently, we do not override abs(), so it fails, although if we do from cpmpy import * just using directly abs() works (because we override it directly in the variables).

just including from builtins import abs in init.py of expressions tackles it

[IgnaceBleukx]

Maybe just put a comment on why specifically we import it here?
And ideally also a test : )

[tias]

this is too sneaky for me, it will be a hidden feature not present in our docs or visible to standard users.

The right way is a new function in python_builtins, with a one-liner documentation, that calls the Abs() global function directly.

Will also make it easier to (generate) tests for...

[Dimosts]

Random not related test is failing .... Will dig into it

[Wout4]

Looks good, thanks for adding tests as well, can be merged

[Wout4]

Do we still want to allow using the builtin abs on our expressions, or should we enforce cpmpy.abs? I guess it's fine to allow it

[Wout4]

@tias looks like you have to approve this now that the 'not' is added :)

[tias]

changed to make the global in the if (without not), seems more logical

also added a comment on the 'any_list', which I still find a bit weird but not a blocker : ) e.g. why it has to be a cpm_array... could have done map(abs, arg) or so, but maybe not worth any further thought