Steve Holden wrote: > I was messing about with formatting and realized that the right kind of > object could quite easily tell me exactly what accesses are made to the > mapping in a string % mapping operation. This is a fairly well-known > technique, modified to tell me what keys would need to be present in any > mapping used with the format.
... > I've been wondering whether it's possible to perform a similar analysis > on non-mapping-type format strings, so as to know how long a tuple to > provide, or whether I'd be forced to lexical analysis of the form string. PyString_Format() in stringobject.c determines the tuple length, then starts the formatting process and finally checks whether all items were used -- so no, it's not possible to feed it a tweaked (auto-growing) tuple like you did with the dictionary. Here's a brute-force equivalent to nameCount(), inspired by a post by Hans Nowak (http://mail.python.org/pipermail/python-list/2004-July/230392.html). def countArgs(format): args = (1,) * (format.count("%") - 2*format.count("%%")) while True: try: format % args except TypeError, e: args += (1,) else: return len(args) samples = [ ("", 0), ("%%", 0), ("%s", 1), ("%%%s", 1), ("%%%*.*d", 3), ("%%%%%*s", 2), ("%s %*s %*d %*f", 7)] for f, n in samples: f % ((1,)*n) assert countArgs(f) == n Not tested beyond what you see. Peter -- http://mail.python.org/mailman/listinfo/python-list
