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Restore cache-clear behavior on a per-path basis.
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Original file line number | Diff line number | Diff line change |
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import types | ||
import functools | ||
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# from jaraco.functools 3.3 | ||
def method_cache(method, cache_wrapper=None): | ||
""" | ||
Wrap lru_cache to support storing the cache data in the object instances. | ||
Abstracts the common paradigm where the method explicitly saves an | ||
underscore-prefixed protected property on first call and returns that | ||
subsequently. | ||
>>> class MyClass: | ||
... calls = 0 | ||
... | ||
... @method_cache | ||
... def method(self, value): | ||
... self.calls += 1 | ||
... return value | ||
>>> a = MyClass() | ||
>>> a.method(3) | ||
3 | ||
>>> for x in range(75): | ||
... res = a.method(x) | ||
>>> a.calls | ||
75 | ||
Note that the apparent behavior will be exactly like that of lru_cache | ||
except that the cache is stored on each instance, so values in one | ||
instance will not flush values from another, and when an instance is | ||
deleted, so are the cached values for that instance. | ||
>>> b = MyClass() | ||
>>> for x in range(35): | ||
... res = b.method(x) | ||
>>> b.calls | ||
35 | ||
>>> a.method(0) | ||
0 | ||
>>> a.calls | ||
75 | ||
Note that if method had been decorated with ``functools.lru_cache()``, | ||
a.calls would have been 76 (due to the cached value of 0 having been | ||
flushed by the 'b' instance). | ||
Clear the cache with ``.cache_clear()`` | ||
>>> a.method.cache_clear() | ||
Same for a method that hasn't yet been called. | ||
>>> c = MyClass() | ||
>>> c.method.cache_clear() | ||
Another cache wrapper may be supplied: | ||
>>> cache = functools.lru_cache(maxsize=2) | ||
>>> MyClass.method2 = method_cache(lambda self: 3, cache_wrapper=cache) | ||
>>> a = MyClass() | ||
>>> a.method2() | ||
3 | ||
Caution - do not subsequently wrap the method with another decorator, such | ||
as ``@property``, which changes the semantics of the function. | ||
See also | ||
http://code.activestate.com/recipes/577452-a-memoize-decorator-for-instance-methods/ | ||
for another implementation and additional justification. | ||
""" | ||
cache_wrapper = cache_wrapper or functools.lru_cache() | ||
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def wrapper(self, *args, **kwargs): | ||
# it's the first call, replace the method with a cached, bound method | ||
bound_method = types.MethodType(method, self) | ||
cached_method = cache_wrapper(bound_method) | ||
setattr(self, method.__name__, cached_method) | ||
return cached_method(*args, **kwargs) | ||
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# Support cache clear even before cache has been created. | ||
wrapper.cache_clear = lambda: None | ||
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return wrapper |