string interpolation (Was: Newbie can't figure out documentation practices)

[Fernando Perez]

Antonios Christofides wrote:

> Fernando Perez wrote:
>>  The only other area where you're likely to cry a bit is proper string
>>  interpolation, which sucks in python.
> 
> You could have been in my mind. My second thread to this group would be
> that the only thing I'm missing badly from Perl is string interpolation.
> So I asked only one of my two -unrelated- questions and got answers to
> both :-)

And as you already saw from the ensuing thread, my view is in the definite
minority around here ;)  But my guess wasn't so much due to my amazing
telepathic abilities, but rather to the fact that you're following the
necessary thought process of a successful perl-to-python conversion.  So
guessing your next moves isn't too difficult at this point :)

Soon you will discover the joys of a clean module system where every file is
automatically an importable library, of data structures which allow you to
build complex, nested things (e.g. lists of dicts of dicts)  with zero pain, or
an object-oriented syntax so trivial that you'll use classes for organizing
data cleanly in many situations.  After that, you'll start wondering why you
needed the Perl cookbook every time you needed a hash of hashes, and couldn't
quite get all the $'s in the right places for all of the dereferences to work
correctly.  Welcome to python!

Note that Sismex's final solution, reproduced again here for convenience's sake,
is a fairly clean approach for the string interpolation issue.  It still
requires the somewhat ugly-looking '%(stuff)modifier' python syntax, but that
syntax has the advantage of allowing very fine control over the output.  So in
the long run it does buy you something new you didn't have in perl :)  Just
keep it around in some 'utils' module you always load, and you won't worry
about the issue again.

Cheers,

f.

##################################
class EvalDict:
    """
    Emulate a dict which evaluates its contents in the caller's frame.

    Usage:
    >>>number = 19
    >>>text = "python"
    >>>print "%(text.capitalize())s %(number/9.0).1f rules!" % EvalDict()
    """

    # This version is due to sismex01 at hebmex.com on c.l.py, and is basically a
    # modified (shorter) version of:
    # http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66018 by
    # Skip Montanaro (skip at pobox.com).

    def __getitem__(self, name):
        frame = sys._getframe(1)
        return eval(name, frame.f_globals, frame.f_locals)