[Python-Dev] Type hints -- a mediocre programmer's reaction (original) (raw)

Terry Reedy tjreedy at udel.edu
Wed Apr 22 08:32:18 CEST 2015

On 4/21/2015 6:41 PM, Chris Barker wrote:

Well, it'll catch passing in a string instead of a sequence of strings -- one of teh common and semi-insidious type errors I see a lot (at least with newbies).

Oh wait, maybe it won't -- a string IS a sequence of strings. That's why this is an insidioous bug in teh first place: List[string] will work, yes -- but now I'm locked down the user to an actual, list, yes? So I try: Iterable[string] ah yes -- now users can use tuples of strings, or a custom class, or -- but wait, darn it, a string IS an iterable of strings.. SIGH.

I was just thinking today that for this, typing needs a subtraction (difference) operation in addition to an addition (union) operation: Difference(Iterable(str), str)

-- Terry Jan Reedy

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