Thank you for the clarification! I should have looked through the PEPs first.
On Thu, Jan 25, 2018 at 10:14 PM, Guido van Rossum <gu...@python.org> wrote: > PEP 526 has this in the "Rejected/Postponed Proposals" section: > > - **Allow annotations in** ``with`` **and** ``for`` **statement:** > This was rejected because in ``for`` it would make it hard to spot the > actual > iterable, and in ``with`` it would confuse the CPython's LL(1) parser. > > > On Thu, Jan 25, 2018 at 3:17 PM, Jelle Zijlstra <jelle.zijls...@gmail.com> > wrote: > >> >> >> 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/mailma >>> n/options/python-dev/jelle.zijlstra%40gmail.com >>> >>> >> >> _______________________________________________ >> 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/guido% >> 40python.org >> >> > > > -- > --Guido van Rossum (python.org/~guido) >
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