how does the % work?
Steven D'Aprano
steve+comp.lang.python at pearwood.info
Sat Mar 23 03:38:23 EDT 2013
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.
--
Steven
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