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From: Nobody <nobody@nowhere.com>
Subject: Re: float("nan") in set or as key
Date: Sat, 04 Jun 2011 20:29:45 +0100
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On Sat, 04 Jun 2011 00:52:17 -0700, rusi wrote:

>> If you're "fluent" in IEEE-754, then you won't find its behaviour
>> unexpected. OTOH, if you are approach the issue without preconceptions,
>> you're likely to notice that you effectively have one exception mechanism
>> for floating-point and another for everything else.
> 
> Three actually: None, nan and exceptions

None isn't really an exception; at least, it shouldn't be used like that.
Exceptions are for conditions which are in some sense "exceptional". Cases
like dict.get() returning None when the key isn't found are meant for
the situation where the key not existing is unexceptional. If you "expect"
the key to exist, you'd use dict[key] instead (and get an exception if it
doesn't).