Is this pythonic?

[Steven D'Aprano]

On Thursday 24 November 2016 15:55, Frank Millman wrote:

> "Steve D'Aprano"  wrote in message
> news:583653bb$0$1603$c3e8da3$5496439d at news.astraweb.com...
> 
>> Even if the computation of the memoised value is done asynchronously, you
>> can easily split the computation off to a separate method (as you already
>> talked about doing!) and make getval() block until it returns.
> 
> Surely that defeats the whole purpose of asyncio. Anything that blocks holds
> up the entire process. I strenuously try to avoid blocking in any shape or
> form.

Perhaps I'm not understanding your task correctly, but surely you have to wait 
for the computation to occur at some point? Even if that's just you hitting 
Refresh waiting for the value of the column to eventually show up.

I'm a newbie to asyncio, but if I were doing this using threads, I'd have 
getval() set the self._cached_value to "pending..." (say), start the 
computation thread running, and then return. The computation thread will 
eventually write the true value to _cached_value, and in the meantime the 
getval() method (and hence __str__ will happily use the "pending..." value. The 
only tricky part is to make sure you only start the thread once.



-- 
Steven
299792.458 km/s — not just a good idea, it’s the law!