[Tutor] string formatting (%s)

[Danny Yoo]

On Sat, 15 Apr 2006, Tiago Saboga wrote:

> Can I use string formatting in my own functions, or is it stuck with builtins?
> It doesn't make much sense for me, but I don't understand the following
> error:
>
> In [1]: var = 456
>
> In [2]: def printd(arg):
>   ...:     print('>>> %s') % arg
>   ...:

Hi Tiago,

Ah!  printd() is not doing what you think it's doing.  Try:

#########################
def printd(arg):
     print ('>>> %s' % arg)
#########################

The parenthesization you had earlier forced Python into printing out your 
template before it had an opportunity to plug arg into it.  You need to do 
the interpolation first.