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Don't panic <wink>.  "and" doesn't evaluate anything twice.  
The subtlety here is that "and" and "or" return one of their 
arguments.  If x evaluates to false in "x and y", then "x and y" 
returns x:

>>> class C:
...     def __nonzero__(self): return False
...
>>> x, y = C(), C()
>>> (x and y) is x
True
>>> (x or y) is y
True
>>>

The second evaluation occurs because "if expr:" has to 
evaluate expr.  That part's got nothing to do with "and", it's 
entirely to do with "if".

None of this is going to change, of course.