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112 lines
3.3 KiB
112 lines
3.3 KiB
6 years ago
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from __future__ import unicode_literals
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from collections import deque
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from functools import wraps
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__all__ = [
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'SimpleCache',
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'FastDictCache',
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'memoized',
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]
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class SimpleCache(object):
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"""
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Very simple cache that discards the oldest item when the cache size is
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exceeded.
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:param maxsize: Maximum size of the cache. (Don't make it too big.)
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"""
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def __init__(self, maxsize=8):
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assert isinstance(maxsize, int) and maxsize > 0
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self._data = {}
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self._keys = deque()
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self.maxsize = maxsize
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def get(self, key, getter_func):
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"""
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Get object from the cache.
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If not found, call `getter_func` to resolve it, and put that on the top
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of the cache instead.
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"""
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# Look in cache first.
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try:
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return self._data[key]
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except KeyError:
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# Not found? Get it.
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value = getter_func()
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self._data[key] = value
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self._keys.append(key)
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# Remove the oldest key when the size is exceeded.
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if len(self._data) > self.maxsize:
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key_to_remove = self._keys.popleft()
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if key_to_remove in self._data:
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del self._data[key_to_remove]
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return value
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def clear(self):
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" Clear cache. "
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self._data = {}
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self._keys = deque()
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class FastDictCache(dict):
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"""
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Fast, lightweight cache which keeps at most `size` items.
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It will discard the oldest items in the cache first.
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The cache is a dictionary, which doesn't keep track of access counts.
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It is perfect to cache little immutable objects which are not expensive to
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create, but where a dictionary lookup is still much faster than an object
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instantiation.
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:param get_value: Callable that's called in case of a missing key.
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"""
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# NOTE: This cache is used to cache `prompt_toolkit.layout.screen.Char` and
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# `prompt_toolkit.Document`. Make sure to keep this really lightweight.
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# Accessing the cache should stay faster than instantiating new
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# objects.
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# (Dictionary lookups are really fast.)
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# SimpleCache is still required for cases where the cache key is not
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# the same as the arguments given to the function that creates the
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# value.)
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def __init__(self, get_value=None, size=1000000):
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assert callable(get_value)
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assert isinstance(size, int) and size > 0
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self._keys = deque()
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self.get_value = get_value
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self.size = size
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def __missing__(self, key):
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# Remove the oldest key when the size is exceeded.
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if len(self) > self.size:
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key_to_remove = self._keys.popleft()
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if key_to_remove in self:
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del self[key_to_remove]
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result = self.get_value(*key)
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self[key] = result
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self._keys.append(key)
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return result
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def memoized(maxsize=1024):
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"""
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Memoization decorator for immutable classes and pure functions.
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"""
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def decorator(obj):
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cache = SimpleCache(maxsize=maxsize)
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@wraps(obj)
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def new_callable(*a, **kw):
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def create_new():
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return obj(*a, **kw)
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key = (a, tuple(sorted(kw.items())))
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return cache.get(key, create_new)
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return new_callable
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return decorator
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