Hi all,

I'm hitting the recursion limit in my code (well, somewhere inside Twisted, that is), and I'd appreciate any insight as to why. I wouldn't think what I'm doing -- returning a callback from method A which calls method B, which then in turn calls method A again -- would be controversial, since I'd assume Python would be letting go of the stack for method A, but I guess there's more to it than that.

Code demonstrating the issue follows. Running it results in:
    File "/usr/lib/python2.5/site-packages/twisted/python/reflect.py", line 550, in accumulateBases
        accumulateBases(base, l, baseClass)
    exceptions.RuntimeError: maximum recursion depth exceeded

(This doesn't actually perfectly reflect my problem in the real code I'm working with. I'm seeing "'maximum recursion depth exceeded' in <bound method DebugInfo.__del__ of <twisted.internet.defer.DebugInfo instance at 0xb1d99b6c>>", but I assume this is coming from the same basic problem in my code.)

===================================

from twisted.internet import defer, reactor

def yo_print(s, d):
    print s
    d.callback(s)
    return s

def some_deferred(item):
    d = defer.Deferred()
    reactor.callLater(0, lambda: yo_print(item, d))
    return d

def start(items):
    dl = []
    for item in items:
        dl.append(some_deferred(item))
        if len(dl) > 4:
            break
    items = items[len(dl):]
    if dl:
        return defer.DeferredList(dl).addCallback(next_batch, items)
    reactor.stop()

def next_batch(_, items):
    return start(items)

if __name__ == '__main__':
    items = []
    for i in range(1651): # 1650 doesn't do it
        items.append(i)
    print start(items)
    reactor.run()

===================================

So I guess the rule is to never, within a callback chain, call a function which was invoked earlier in the callback chain?

Steve