[Python-Dev] why doesn't print pass unicode strings on to the file object?

[Guido van Rossum]

> Because I'd like to avoid an inflation of functions. Instead, I'd
> prefer codecs.lookup to return an object that has the needed fields,
> but behaves like a tuple for backwards compatibility.

Here's how you can do that in 2.2a3 (I wrote this incomplete example
for another situation :-):

    class Stat(tuple):
	def __new__(cls, t):
	    assert len(t) == 9
	    self = tuple.__new__(cls, t[:7])
	    self.st_seven = t[7]
	    self.st_eight = t[8]
	    return self
	st_zero = property(lambda x: x[0])
	st_one = property(lambda x: x[1])
	# etc.

    t = (0,1,2,3,4,5,6,7,8)
    s = Stat(t)

    a,b,c,d,e,f,g = s
    assert (a, b, c, d, e, f, g) == t[:7]
    assert t == s + (s.st_seven, s.st_eight)

> > Note that the tuple interface was chosen for sake of speed and
> > better handling at C level (tuples can be cached and are easily
> > parseable in C).

Alas, a tuple subclass loses some of the speed and size advantage --
the additional instance variables require allocation of a dictionary.

(And no, you cannot use __slots__ here -- the slot access mechanism
doesn't jive well with the variable length tuple structure.  If we
were to subclass a list, we could add

    __slots__ = ["st_seven", "st_eight"]

to the class.  But that's not fully tuple-compatible.)

--Guido van Rossum (home page: http://www.python.org/~guido/)