Allow float window when using .rolling

[gliptak]

• closes ERR: better error message on invalid window when using .rolling #12669
• tests added
• passes git diff upstream/master | flake8 --diff
• whatsnew entry

#12669

[jreback]

this needs to raise if its not an integer for Rolling and sub-classes, or int/array of ints for Window

[gliptak]

@jreback So pd.DataFrame(np.arange(10)).rolling(2.).median() should work, while pd.DataFrame(np.arange(10)).rolling(2., center=True).median() should fail with argument validation (only difference is center=True)? Can you confirm?

[jreback]

neither would wifi now should be an int if not it's an error

[shoyer]

I just noted in the associated issue that that I think it would be better to raise than coerce integers.

It could be OK to accept floats if int(window) == window, but window=2.5 should definitely raise an error.

[jreback]

I agree we should just raise on non-int. I think was an oversight in the initial impl. yes its safe if int(x) == x, but more correct to raise TypeError as @shoyer suggests.

[jreback]

competing PR is #12718

[jreback]

@gliptak want to update (also see my comments on the competeting PR).