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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.zijlstra@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.

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