The documentation for the `async for` statement incorrectly states that "An asynchronous iterable is able to call asynchronous code in its iter implementation". Actually, this behavior was deprecated in Python 3.6 and removed in Python 3.7.  As of Python 3.7, the `__aiter__()` method must return an asynchronous iterator directly.

Suggested fix: Update the `async for` statement description for Python 3.7+ to match the "Asynchronous Iterators" section in the data model documentation.

> An :term:`asynchronous iterator` can call asynchronous code in its *next* method.

Relevant documentation:
- https://docs.python.org/3/reference/compound_stmts.html#the-async-for-statement
- https://docs.python.org/3/reference/datamodel.html#asynchronous-iterators