On Thursday 19 April 2007, Bill Jackson wrote:
> Martin v. Löwis wrote the following on 04/19/2007 02:43 PM:
> > Bill Jackson schrieb:
> >> I have a dictionary of dictionaries where the keys are typically very
> >> long tuples and repeated in each inner dictionary.
> >
> > What I don't understand here: you say the keys are tuples, yet later,
> > you show that the keys are strings. Which one is it?
>
> Sorry, I was just lazy. The keys will always be tuples...tuple of
> strings, tuples of numbers, tuples of objects....simply tuples.
That'll change things a bit because intern only works with strings.
Of course, It's not so big a deal, but you will have to put together a class
to implement interning.
I wrote one for fun:
class ITuple(tuple):
_interns={}
def __new__(cls, tup):
if tup not in cls._interns:
itup=tuple.__new__(cls, tup)
cls._interns[tup]=itup
return cls._interns[tup]
def __init__(self, *args):
#Prevent multiple calls to __init__
if hasattr(self, "_inited"): return
tuple.__init__(self, *args)
self._inited=True
def __eq__(self, o):
#If the other is an ITuple, self==o iff self is o
if isinstance(o, ITuple):
return self is o
return tuple.__eq__(self, o)
>>> t1=(1,2,3,4); t2=(1,2,3,4)
>>> ti1=ITuple(t1); ti2=ITuple(t2)
>>> print t1==t2, t1 is t2
True False
>>> print ti1==ti2, ti1 is ti2
True True
That seems to work. Something to note is that the call overhead of the __eq__
function is large enough that unless you have a slow comparing tuple,
comparisons will be faster without it. Comparisons are fast if they are done
internally; so between builtin objects or identical (" is ") objects.
For an example, suppose you have:
class TTT(object):
def __eq__(self, o): return True
a,b=TTT(),TTT()
Then the follow comparisons are fast:
(1,2,3)==(1,2,3)
(1,2,3,a)==(1,2,3,a)
(0,0,0,a)==(1,2,3,b)
The following are slow:
(1,2,3,a)==(1,2,3,b)
Note that the only slow case is the one where a.__eq__(b) is called. However,
a.__eq__(b) is assumed True is "a is b" is True. So chances are you'll want
to comment out the __eq__ function.
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