Weird asyncore behaviour

[Andrew Bennetts]

On Mon, Nov 03, 2003 at 09:34:23AM +1030, Freddie wrote:
> Hi,
> 
> I've been playing around with asyncore for one of my projects, currently 
> using it to fetch HTTP pages without blocking things. Having a few 
> issues, though. With the code below, I would start a new async_http 
> instance with "async_http(url, returnme)". If it encountered a redirect, 
> that object would start a new one as "async_http(url, returnme, 
> seen=self._seen)" to remember what URLs it had seen. The problem is that 
> after a while (usually after several async_http objects are active at 
> once), newly created async_http objects would have the seen parameter 
> with URLs filled in already! I have absolutely no idea how that could be 
> happening :\ I 'solved' it by explicitly passing "seen={}" for new 
> objects, but I would still like to know why this is happening :)
> 
> Freddie
> 
> 
> class async_http(asyncore.dispatcher):
> 	def __init__(self, parent, returnme, url, seen={}):

That line is the problem.  Default arguments are only created once, at
function definition time, not every time the function is called.  So the
same 'seen' dictionary is being used for all async_http instances.
Generally, rather than using mutable default arguments, do:

    def __init__(self, parent, returnme, url, seen=None):
        if seen is None:
            seen = {}
        ...

-Andrew.