[Python-Dev] from tuples to immutable dicts (original) (raw)

Martin v. Loewis martin@v.loewis.de
24 Nov 2002 18:10:54 +0100

This goes against the initial proposal, which was to have a lightweight and declaration-less way to build structures.

Yes. I never had the need for a lightweight and declaration-less way to build structures. What is the need?

point = {'x': 5, 'y': 6} print point['x'] print point['y']

which looks reasonably if not quite entierely nice.

If looking reasonable, or even nice, is the goal, why not write

class Point: def init(self, x, y): self.x, self.y = x, y

point = Point(5, 6) #or point = Point(x=5, x=6)

print point.x print point.y

The problem is that it is incompatible with tuples: you cannot smoothly go from tuples to dicts without changing your whole program.

So you need to enhance class Point

def getitem(self, index): if index == 0:return self.x if index == 1:return self.y raise IndexError

What about just allowing keyword parameters in 'tuple'?

point = tuple(5, 6, color=RED, visible=False)

I have to problems imagining such an extension:

I'm not sure this would be useful.
I can't imagine how to implement it, without compromising performance for tuples.
It can be easily implemented without any change to builtin types:

class Tuple(tuple): pass

def TUPLE(*args, **kw): res = Tuple(args) res.dict=kw return res

point = TUPLE(5, 6, color="RED", visible=False) print point[0] print point.color

Regards, Martin