String formatters with variable argument length

[John Machin]

Fredrik Tolf wrote:
> I've been trying to get the string formatting operator (%) to work with
> more arguments than the format string requires, but I can find no way to
> do that. For example:
>
> >>> "%i" % 10
> '10'
> >>> "i" % 10
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: not all arguments converted during string formatting
>
> The thing is, I want to get format strings from the user, and I don't
> want to require the user to consume all the arguments. docs.python.org
> doesn't seem to have any clues on how to achieve this, and I can't think
> of what to google for.
>
> Could it be as I fear, that it is impossible?
>

Three approaches spring to mind. In descending order of my preference:

(a) don't do that

(b) parse the format string, counting the number of args required. If
the user has supplied more, throw them away.

(c) wrap your execution of format_string % args in a try/except
bracket. If you get a TypeError with that message [not guaranteed to
remain constant in the future], throw away the last arg and go around
again.

As a matter of curiosity, why don't you want the user to consume all
the arguments? Don't they get even a teensy-weensy warning message? Are
you writing a Perl interpreter in Python?

Cheers,
John