I find checking for "is None" very useful, but that is also the only time I use 'is'. I try to avoid checking for True-ish and False-ish whenever possible, preferring to be more explicit.
Yet the same be benefits of explicit None checks can be attained by writing "== None" i.e. doing value based comparisons against a None value. So this argument does not explain why "is" is necessary.
class C:
def __eq__(self, other): return True
C() == None # True
C() is None # False el==None
el is None
None==el
If you are going to do that's you should probably do a backwards comparison (`None==x`), otherwise you are calling x.__eq__(None), which probably won't be surprising in result if you have constrained things with sane typing, but still could be more expensive than `x is None`.
`x is None` reads a lot better though.