how does the % work?

leonardo tampucciolina at libero.it
Sat Mar 23 18:05:20 CET 2013


thank you all!


Il 23/03/2013 8.38, Steven D'Aprano ha scritto:
> On Fri, 22 Mar 2013 21:29:48 -0700, Tim Roberts wrote:
>
>> leonardo selmi <l.selmi at icloud.com> wrote:
>>> i wrote this example :
>>>
>>> name = raw_input("What is your name?")
>>> quest = raw_input("What is your quest?")
>>> color = raw_input("What is your favorite color?")
>>>
>>> print """Ah, so your name is %s, your quest is %s, and your favorite
>>> color is %s."""  % (name, quest, color)
>> No, you didn't.  You wrote:
>>
>> print('''Ah, so your name is %s, your quest is %s, and your
>>      favorite color is %s.''') % (name, quest, color)
>
> The difference between those two statements may not be entirely clear to
> someone not experienced in reading code carefully.
>
> Consider the difference between:
>
>    print(a % b)
>
>    print(a) % b
>
> In the first example, the round brackets group the "a % b", which is
> calculated first, then printed.
>
> In the second example, in Python 3, the "print(a)" is called first, which
> returns None, and then "None % b" is calculated, which raises an
> exception.
>
> Just to add confusion, the two lines are exactly the same in Python 2,
> where Print is not a function!
>
>
>> You are using Python 3.  In Python 3, "print" is a function that returns
>> None.  So, the error is exactly correct.  To fix it, you need to have
>> the % operator operate on the string, not on the result of the "print"
>> function:
>>
>> print('''Ah, so your name is %s, your quest is %s, and your
>>      favorite color is %s.''' % (name, quest, color))
> Exactly correct.
>
>
>




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