Question about defaultdict
Peter Otten
__peter__ at web.de
Sat Feb 23 06:02:21 EST 2013
Frank Millman wrote:
> On 23/02/2013 12:13, Frank Millman wrote:
>> Hi all
>>
>> I use a dictionary as a cache, and I thought that I could replace it
>> with collections.defaultdict, but it does not work the way I expected
>> (python 3.3.0).
> >
> [...]
>>
>> from collections import defaultdict
>> my_cache = defaultdict(fetch_object)
>> my_obj = my_cache['a']
>>
>> It does not work, because fetch_object() is called without any arguments.
>
> Thanks, Chris and Peter. Some nice ideas to choose from :-)
>
> Frank
Oh, I overlooked that you are using Python 3. For that there's also
functools.lru_cache. Example:
>>> from functools import lru_cache
>>> @lru_cache(maxsize=None)
... def fetch_object(id):
... print("fetching #{}".format(id))
... return id*id # bogus example
...
>>> fetch_object(42)
fetching #42
1764
>>> fetch_object(42)
1764
>>> fetch_object(10)
fetching #10
100
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