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Mon Jan 19 20:18:47 EST 2004 · https://mail.python.org/pipermail/python-dev/2004-January/042105.html

On Jan 19, 2004, at 6:36 PM, François Pinard wrote:

> [Guido van Rossum]
>> Marcin 'Qrczak' Kowalczyk <qrczak at knm.org.pl> writes:
>
>>> Now thow in 'isinstance' as an old way to spell a specific membership
>>> test (for types and classes) which doesn't have to be learned about
>>> at all.
>
>> I love it.  'x in type' as a shorthand for isinstance(x, type).
>> Checked into CVS!
>
> The above exchange is dated 2001-07-31, and I'm merely glancing over
> some old saved email.  The above feature does not seem to be 
> implemented
> in Python 2.3.2, as demonstrated by the script below.  Has it been
> retracted?  Not that I really need it, however! :-)

I don't know what happened to this before, but I'd give it a -1.. it 
breaks some "fun" uses of metaclasses where you have a desire to use 
__contains__.  For example, I use an enumeration class as a container 
for enumerators.. the enumeration metaclass implements __contains__, 
__getitem__, and a few other things.

Anyways, why not:
mytype in type(foo).mro()

(and add support for old style classes, if you still use them)

-bob

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[Python-Dev] Re: 2.2 features