String interpolation question

[Michael Hudson]

Fernando Pérez <fperez528 at yahoo.com> writes:

> Thanks for your suggestions. Basically imagine having many arrays
> and needing to generate output of the form (this is perl syntax,
> which for once is a million times cleaner than python for _this_
> problem):
> 
> print "$i arr1[$i]=$arr1[$i] arr2[$i]=$arr2[$i] arr3[$i]=$arr3[$i] ....\n";

When I found myself doing this, I wrote something like this:

import re

template = """\
def copy_array(self, arr1, arr2):
    {{ arr1[!] = arr2[!]; }}
"""

prog = re.compile("\\{\\{.*?\\}\\}")

def expand_template(template, n):
    def replacer(match):
        s = match.group(0)[2:-2]
        r = []
        for i in range(n):
            r.append(s.replace('!', `i`))
        return ''.join(r)
    return prog.sub(replacer, template)

then:

>>> print expand_template(template, 3)
def copy_array(self, arr1, arr2):
     arr1[0] = arr2[0];  arr1[1] = arr2[1];  arr1[2] = arr2[2]; 

>>> 

I say "something like" because my code was a bit less trivial, came
before nested scopes, and I can't quite remember the markup I used.

Ah yes, more here:

http://groups.google.com/groups?selm=m31ziyfy28.fsf_-_%40atrus.jesus.cam.ac.uk

> To me, the above line is clear, unambiguous and requires zero contortions to 
> either write or read (by the coder). 

To me it looks scarily long...

HTH,
M.

-- 
  incidentally, asking why things are "left out of the language" is
  a good sign that the asker is fairly clueless.
                                        -- Erik Naggum, comp.lang.lisp