Re: Boolean tests [was Re: Attack a sacred Python Cow]

Steven D'Aprano wrote:
On Wed, 30 Jul 2008 09:23:05 -0600, Matthew Fitzgibbons wrote:

If you're expecting a list (and only a list)
then your point makes sense. 'if x' can get you into trouble if you
_don't_ want its polymorphism.

"if x" is hardly unique in that way. If you're expecting a list, and only a list, "len(x) != 0" will get you in trouble if somebody passes a string or a dictionary. I don't see any reason why we should single out "if x" as dangerous in the face of invalid types. With the exception of the "is" and "is not" operators, nothing in Python is guaranteed to work with any imaginable object. Even print can fail, if the object's __str__ method raises an exception.

Forgot respond to this point. I heartily agree. :) I singled out 'if x' only because that's the specific example under scrutiny. I think you and I are pretty much in agreement.

-Matt
.

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