I'm primarily a PHP developer who knows enough Python and admires the ecosystem from a distance (not that that's relevant for this discussion).
So I've been following the development of async Web frameworks in Python and am impressed that the community has responded rather quickly to the "Node threat" by producing async, highly performant frameworks. PHP has developed some solutions for this, but they are not even primitive.
Anyway, so, the question is this: what are the practical limitations of such async web frameworks?
I remember a point of discussion (though I can't remember where I came across it or in which language ecosystem) that the async framework in question doesn't give much practical benefit as almost all the popular libraries were written in a synchronous manner. I mean, Node was created with async in mind so has excellent support for it (but poor support for multi-core machines :P), which is why it excels at what it advertises.
Is this something that affects the Python's async web frameworks? What unpleasant surprises lie in wait for the unsuspecting enthusiastic developer should he choose to adopt one of these frameworks?