2018-01-25 15:00 GMT-08:00 Joe Jevnik via Python-Dev <python-dev@python.org> :
> Currently there are many ways to introduce variables in Python; however, > only a few allow annotations. I was working on a toy language and chose to > base my syntax on Python's when I noticed that I could not annotate a loop > iteration variable. For example: > > for x: int in range(5): > ... > > This led me to search for other places where new variables are introduced > and I noticed that the `as` target of a context manager cannot have an > annotation. In the case of a context manager, it would probably need > parenthesis to avoid ambiguity with a single-line with statement, for > example: > > with ctx as (variable: annotation): body > > Finally, you cannot annotate individual members of a destructuring > assignment like: > > a: int, b: int, c: int = 1, 2, 3 > > Looking at the grammar, these appear to be `expr` or `exprlist` targets. > One change may be to allow arbitrary expressions to have an annotation . > This would be a small change to the grammar but would potentially have a > large effect on the language or static analysis tools. > > I am posting on the mailing list to see if this is a real problem, and if > so, is it worth investing any time to address it. I would be happy to > attempt to fix this, but I don't want to start if people don't want the > change. Also, I apologize if this should have gone to python-idea; this > feels somewhere between a bug report and implementation question more than > a new feature so I wasn't sure which list would be more appropriate. > I have written a fair amount of code with variable annotations, and I don't remember ever wanting to add annotations in any of the three contexts you mention. In practice, variable annotations are usually needed for class/instance variables and for variables whose type the type checker can't infer. The types of loop iteration variables and context manager assignment targets can almost always be inferred trivially. > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ > jelle.zijlstra%40gmail.com > >
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