Making string-formatting smarter by handling generators?

[Arnaud Delobelle]

On Feb 27, 4:23 pm, Tim Chase <python.l... at tim.thechases.com> wrote:
> Is there an easy way to make string-formatting smart enough to
> gracefully handle iterators/generators?  E.g.
>
>    transform = lambda s: s.upper()
>    pair = ('hello', 'world')
>    print "%s, %s" % pair # works
>    print "%s, %s" % map(transform, pair) # fails
>
> with a """
> TypeError:  not enough arguments for format string
> """
>
> I can force it by wrapping the results of my generator in a call
> to tuple() or list()

(Are you using python 3.0 ? For python < 3, map returns a list)

list() wouldn't work as % expects a tuple (otherwise it considers that
only one argument is needed).  The problem would arise with any non-
tuple iterable, not just generators.

See http://docs.python.org/lib/typesseq-strings.html

>
>    print "%s, %s" % tuple(map(transform, pair))
>
> but it feels a bit hackish to me.

I think it is the way to do it though.

> I find I hit it mostly with calls to map() where I want to apply
> some transform (as above) to all the items in a list of
> parameters such as
>
>    "%s=%s&%s=%s" % map(urllib.quote, params)
>
> Any suggestions?  (even if it's just "get over your hangup with
> wrapping the results in list()/tuple()" :)

get over your hangup with wrapping the results in tuple()! (not list()
though, as explained above).

Or you could always define

def tmap(*args):
    return tuple(map(*args))

--
Arnaud