sufficiently pythonic code for testing type of function

[Fredrik Lundh]

Theerasak Photha wrote:

> I'll do that as soon as my green noggin figures out what 'idempotent' means.

"Acting as if used only once, even if used multiple times", to quote
the first explanation I saw on the google result page.

and from the irony department, googling for "indempotent" provides an 
even clearer explanation: "Refers to an operation that produces the same 
results no matter how many times it is performed."

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