I don't think it's quite what you're talking about, but I have an Emacs function that runs the current region through Python and replaces it with the stdout from running it.

For your example, I write this:

    vars = list('abcdefghijklm')
    for v,i in zip(vars, range(len(vars))):
        print("#define {} {}".format(v, i))

Select it and press Ctrl+Alt+p and have it replaced by:

    #define a 0
    #define b 1
    #define c 2
    #define d 3
    #define e 4
    #define f 5
    #define g 6
    #define h 7
    #define i 8
    #define j 9
    #define k 10
    #define l 11
    #define m 12

https://gist.github.com/1355548