On Tue, 9 Mar 2021, at 19:28, Glyph wrote:
>
>
> > On Mar 9, 2021, at 4:54 AM, Peter Westlake <[email protected]> wrote:
> >
> > I'm getting a "maximum recursion depth exceeded" error that appears to be
> > coming from flatten(). The odd thing is that it only happens sometimes. The
> > HTML that's being flattened does have a few Deferreds in it. Those come
> > from function calls, which cache the results, which might explain why I
> > only see the error on the first visit to the page (as far as I can tell).
> >
> > The system recursion limit is the standard 1000. My HTML is only nested a
> > few tags deep, two orders of magnitude short of that. Is there anything
> > about the way flatten() works that might cause this behaviour?
>
> flatten() can definitely result in some deep recursive stacks,
> particularly in combination with synchronous Deferreds which have their
> own accumulating stack costs. I'd be interested to see a minimal
> reproducer for this though, I'm sure we could do a lot better.
Here it is:
import sys
from twisted.internet import reactor, defer, task
from twisted.web.template import flatten
def output(stuff):
sys.stdout.write(stuff.decode())
def sync(reactor):
return flatten(None, [defer.succeed(str(i)+'\n') for i in range(1000)],
output)
task.react(sync)
It fails after printing 197 lines. The same sort of thing using deferLater
instead of defer.succeed printed 1000 without error.
Peter.
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