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Date: Thu, 16 Aug 2012 19:11:19 -0400
From: Dave Angel <davea@dejaviewphoto.com>
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To: Paul Rubin <no.email@nospam.invalid>
Subject: Re: set and dict iteration
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On 08/16/2012 05:26 PM, Paul Rubin wrote:
> Dave Angel <d@davea.name> writes:
>> Everything else is implementation defined.  Why should an implementation
>> be forced to have ANY extra data structure to detect a static bug in the
>> caller's code?
> For the same reason the interpreter checks for type errors at runtime
> and raises TypeError, instead of letting the program go into the weeds.

There's an enormous difference between type errors, which affect the low
level dispatch, and checking for whether a dict has changed and may have
invalidated the iterator.  If we were really going to keep track of what
iterators are tracking a given dict or set, why stop there?  Why not
check if another process has changed a file we're iterating through?  Or ...