En Wed, 27 Feb 2008 20:40:04 -0200, Tim Chase <[EMAIL PROTECTED]> escribió:
>>> Note that your problem has nothing to do with map itself. >>> String interpolation using % requires either many individual >>> arguments, or a single *tuple* argument. A list is printed >>> as itself. > > Just as an exercise to understand this better, I've been trying > to figure out what allows for this interpolation. It doesn't > seem to be via duck-typing: > > >>> # what does a tuple have that a list doesn't > >>> tuple_set = set(dir(tuple())) > >>> list_set = set(dir(list())) > >>> tuple_set - list_set > set(['__getnewargs__']) > > class LikeATuple(list): > def __getnewargs__(self, *args, **kwargs): > pass # now have everything dir(tuple()) has > f = LikeATuple((1,2,3)) > print "%s, %s, %s" % f > > However, if I create a class that derives from a tuple(), it > seems to work fine: > > class MyTuple(tuple): > pass > f = MyTuple((1,2,3)) > print "%i, %i, %i" % f > > it works fine. Is there some secret attribute that I'm missing? Yes: the class itself :) The code checks whether the right argument is a tuple (or subclass of), or a generic mapping. Checking *only* for tuples allows one to usually write "%s" % thing, and only bother to write "%s" % (thing,) when such `thing` could actually be a tuple. Mappings don't have that problem, because the left operand must be written in a different form so Python knows when to treat the right operand as a mapping. See my previous response to Steven D'Aprano. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
