[Tutor] What's the difference between %s and %r?

[Martin A. Brown]

Hello everybody,

 : > Hello! I'm having troubles understanding what is the difference between %s
 : > and %r(format characters). I did google  and found something on
 : > StackOverflow but I don't understand the explanation as it's not beginner
 : > orientated.
 : >
 : >
 : > Also, I have this code from learn python the hard way. Why at line 9 does
 : > he uses %r? Why did he didn't wrote print "I said: %s." %x ?
 : >
 : > 1    x = "There are %d types of people." % 10
 : > 2    binary = "binary"
 : > 3    do_not = "don't"
 : > 4    y = "Those who know %s and those who %s." % (binary, do_not)
 : > 5
 : > 6    print x
 : > 7    print y
 : > 8
 : > 9    print "I said: %r." % x
 : > 10  print "I also said: '%s'." % y
 : > 11
 : > 12  hilarious = False
 : > 13  joke_evaluation = "Isn't that joke so funny?! %r"
 : > 14
 : > 15  print joke_evaluation % hilarious
 : > 16
 : > 17  w = "This is the left side of..."
 : > 18  e = "a string with a right side."
 : > 19
 : > 20  print w + e
 : >
 : >
 : >
 : > Thanks in advance!
 : 
 : I have recently worked through that exact question myself.  And 
 : it isn't well explained.
 : 
 : So - the simplistic answer, gleaned (hopefully not erroneously) 
 : from this list:  s means a string, d means a number and r can be 
 : either or both.  y has only words, so is a string, and x has a 
 : number (specifically referred to as d) and words, so needs r.

I am not horrendously well-versed here, but consider the mnemonic.

  %f   float
  %d   digit
  %s   string
  %r   representation

A representation is something that (might?) allow for some sort of 
round-trip, later (re)construction of the object.  A string is 
intended for general consumption.  Do you really need to distinguish 
them?  Only if you plan on re-consuming your own output, at which 
point you should consider the representation rather than the string.

There are doubtless more experienced hands here who will suggest 
concretely what you might do, but I would suggest that you use %s 
(string) for anything that you want to show to an end user and %r 
iif* you are planning to (re-)consume your own printed output.

-Martin

 * iif = if and only if

-- 
Martin A. Brown
http://linux-ip.net/