On Mar 5, 5:31 pm, Grant Edwards <[EMAIL PROTECTED]> wrote:
> On 2008-03-05, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> > Anyway, if (a,b) is a key in dictionary d, can it guarantee
> > that (b,a) is also in it, and maps to the same object?
Er... -specialized- dictionary d.
> To solve that problem, Python provides the immutable
> "frozenset" type:
>
> >>> s1 = frozenset((1,2))
> >>> s2 = frozenset((2,1))
> >>> s1 == s2
> True
> >>> d = {s1: "hi there"}
> >>> s1 in d
> True
> >>> s2 in d
> True
Ah. Perfect. With this, I can just call frozenset on keys in
__setitem__ and __getitem__... (though at that, it may be easier
verbatim*.)
*loosely introduced terminology, roughly equivalent to 'spell it out
by hand each time'**.
**__delitem__ too.
Only thing is, that's an extra check if 'key' is iterable.
(Yes. I realize this is a little scattered... it's my belief it's
intelligible by party X... if not stop now speak up.)
Goal:
assert d[1,2] is d[2,1]
assert d[1] is d[1]
assert d[a] is d[a]
assert d[a,b] is d[b,a]
Only problem is, if a is iterable, then its contents get hashed. I
don't see the general way around this.
a= SomeList( [ 1,2,3 ] )
b= SomeList( [ 1,2,3 ] )
assert a is not b
d[a]= True
assert b not in d
#there's the hangup
It is my loss that M. Roggisch plonks me-- I will be deprived of his
perspective and contributions.
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