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85 lines
2.2 KiB
Python
85 lines
2.2 KiB
Python
import functools
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class _HashedSeq(list):
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# # From CPython
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__slots__ = 'hashvalue'
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def __init__(self, tup, hash=hash):
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self[:] = tup
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self.hashvalue = hash(tup)
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def __hash__(self):
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return self.hashvalue
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# if we only have nonlocal
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class _Cache(object):
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def __init__(self):
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self.off = False
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self.missed = 0
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self.cache = {}
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def function_cache(expected_max_entries=1000):
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"""
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function_cache is a decorator for caching function call
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the argument to the wrapped function must be hashable else
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it will not work
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expected_max_entries is for protecting cache failure. If cache
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misses more than this number the cache will turn off itself.
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Specify None you sure that the cache will not cause memory
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limit problem.
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Args:
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expected_max_entries(integer OR None): will raise if not correct
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Returns:
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function
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"""
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if (
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expected_max_entries is not None and
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not isinstance(expected_max_entries, int)
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):
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raise TypeError(
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'Expected expected_max_entries to be an integer or None'
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)
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# indicator of cache missed
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sentinel = object()
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def decorator(func):
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cached = _Cache()
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@functools.wraps(func)
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def inner(*args, **kwargs):
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if cached.off:
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return func(*args, **kwargs)
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keys = args
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if kwargs:
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sorted_items = sorted(kwargs.items())
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for item in sorted_items:
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keys += item
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hashed = hash(_HashedSeq(keys))
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result = cached.cache.get(hashed, sentinel)
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if result is sentinel:
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cached.missed += 1
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result = func(*args, **kwargs)
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cached.cache[hashed] = result
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# # something is wrong if we are here more than expected
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# # empty and turn it off
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if (
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expected_max_entries is not None and
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cached.missed > expected_max_entries
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):
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cached.off = True
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cached.cache.clear()
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return result
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return inner
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return decorator
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