Check in for an instance of a class

[Aahz Maruch]

In article <59f8895f.0112251925.26c43cc at posting.google.com>,
Ben Graham <musk_ben at yahoo.com> wrote:
>
> I need to check whether an instance of a particular class exists, in
>its __init__(...). Assuming that the module containing the class may
>or may not be imported, what are the my options? (As far as possible,
>I would like to contain the test in the class completely). And, yes, I
>need a pre-2.2 solution.

Just use a class variable:

class C:
    InstanceCreated = None
    
    def __init__(self):
        if C.InstanceCreated is None:
            ...
            C.InstanceCreated = 1
        else:
            ...
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