Originally brought up on StackOverflow, https://stackoverflow.com/questions/60799366/nested-async-comprehension :

This dict comprehension parses and works correctly:

async def bar():
    return {
        n: await foo(n) for n in [1, 2, 3]
    }

But making it nested fails with a SyntaxError:

async def bar():
    return {
        i: {
            n: await foo(n) for n in [1, 2, 3]
        } for i in [1,2,3]
    }

The error reported is:

  File "<stdin>", line 0
SyntaxError: asynchronous comprehension outside of an asynchronous function