Revisiting PEP 505

[jamesdow21 (James Dow)]

I had participated a bit in one of the previous threads about this PEP a few months ago and had come to the realization that the ?. and ?[] operators both made a lot of intuitive sense if you instead treated the ? as a unary postfix operator

@jamesdow21

I’ve realized that there is a key part of how I’ve been mentally “framing” and parsing each of these that is actually not stated in the PEP at all (and at a quick skim, the PEP seems to be rejecting outright).

When I’ve been reading obj?.attr, I think of it as obj? .attr not obj ?.attr

i.e. the question that I’m asking in the expression is “Is obj None?”, not “Does obj have attr?”

“Is obj None?” is equivalent to None if obj is None else obj.attr
whereas “Does obj have attr?” is equivalent to getattr(obj, "attr", None)

I’ll also add a shameless plug for a very long comment I made showing how the None-aware operators (and specifically just None-aware, not AttributeError or KeyError silencing) can be quite useful in a real world use case I have in my job doing analysis for a manufacturing company.

The overall point there is that if you are dealing with a entity-relationship model, long chains of attribute lookups are quite reasonable and in many cases it is an expected case that there could be a null value somewhere along the chain since relationships can be “total” (i.e. required/non-null) or “partial” (i.e. nullable) and the natural way to express that in Python is by using None