On Sep 13, 5:36 am, byron <[EMAIL PROTECTED]> wrote:
> I am reading o'reilly's learning python (great book), but i came
> across an example (pg 291, pdf) that I am not quite understanding the
> reasoning for the author's explanation:
>
> if f1() or f2():
>
> The author states that do to the nature of that expression, if f1()
> returns True, f2() will not be evaluated.. which makes sense. His
> quote:
>
> "Here, if f1 returns a true (or nonempty) value, Python will
> never run f2."
>
> He then states:
>
> "To guarantee that both functions will be run, call them
> before the 'or':"
>
> tmp1, tmp2 = f1(), f2()
> if tmp1 or tmp2:
>
> Being that each function is an object, a name assignment to
> (tmp1,tmp2) doesn't actually evaluate or run the function itself until
> the name is called.. so why would the latter example "run" both
> functions as the author suggests?
It's not a "name assignment".
In effect it's doing this:
tmp1 = f1() # get the RESULT of calling f1()
tmp2 = f2() # likewise f2
if tmp1 or tmp2: # if result1 or result2
A (pointless) "name assignment") with the nil effect that you fear
would look like this:
tmp1, tmp2 = f1, f2 # Look, no parentheses after function names
if tmp1() or tmp2():
HTH,
John
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