>
> >>>> [].sort() is None
> > True
> >>>> "ABC".lower() is None
> > False
> >
> > That's a deliberate design choice, and one that has been explained a
> > few times on the list when folks ask why "[].sort().reverse()" doesn't
> > work when "'ABC'.lower().replace('-', '_')" does.
> >
> > Would it be worth adding such a note? Or is it out of scope?
>Is there a reference anywhere as to *why* the convention in Python is to do it that way? Personally, I often miss the ability to chain operations on mutable objects, but I can only imagine that that design decision was made for good reason. However, as I teach Python, I find I have nothing to say other than "that's the way it's done in Python". I note in a way that there is a bit of backwards logic: immutable objects **have** to return something, so they naturally chain. It's almost as if the philosophy of the language is that you don't want chaining behavior, and it's really just a side effect of immutables that you get it with them. I suppose the argument could be that for mutable objects, returning None is an indicator that you are a) working with an mutable object, and b) that the method changes the internal state. But the .pop() example demonstrates that a method can both return something meaningful, and change internal state, so I'm not sure it's really a distinction worth making. So again: is there a clear explanation of the logic behind the convention posted somewhere? -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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