Roger wrote:
And, just for completeness, the "is" test is canonical precisely because
the interpreter guarantees there is only ever one object of type None,
so an identity test is always appropriate. Even the copy module doesn't
create copies ...
Does the interpreter guarantee the same for False and True bools?
Yes. Bool(x) should return one of the two existing instances.
In 2.x, the *names* 'True' and 'False' can be rebound because bool is
new and people write
try:
False,True
except NameError:
False,True = 0,1
to make code back compatible.
In 3.0, the names are keywords, just like 'None' and cannot be rebound,
so x is True is guaranteed to answer whether x *is* the true object.
Back before rebinding 'None' was prohibited, 'is None' was not
completely guaranteed either (absent reading the rest of a file to be
sure no rebinding would be done).
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