On 21 Jul 2005 19:29:32 -0700, "Raymond Hettinger" <[EMAIL PROTECTED]> wrote:
>[Will McGugan]
>> I need a collection class that behaves like a dictionary but when it
>> reaches 'n' items it discards the oldest item so that the length never
>> goes above 'n'. (Its for caching search results)
>
>
>import collections
>
>class Cache(dict):
> def __init__(self, n, *args, **kwds):
> self.n = n
> self.queue = collections.deque()
> dict.__init__(self, *args, **kwds)
> def __setitem__(self, k, v):
> self.queue.append(k)
> dict.__setitem__(self, k, v)
> if len(self) > self.n:
> oldk = self.queue.popleft()
> del self[oldk]
>
> # . . .
> # make similar modifications to setdefault, __delitem__, fromkeys
> # and other mutating methods as needed
>
># Example
>c = Cache(3)
>for w in 'the quick brown fox jumped over the lazy dog'.split():
> c[w] = w[:1].upper()
> print repr(c)
>
Minor comment: There is a potential name collision problem for keyword
n=something,
so what is considered best practice to avoid that? __n or such as the n arg?
>>> def foo(n, *args, **kw): print n, args, kw
...
>>> foo(1)
1 () {}
>>> foo(n=5)
5 () {}
>>> foo(3, n=5)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: foo() got multiple values for keyword argument 'n'
>>>
Regards,
Bengt Richter
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