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1import functools
2import types
5# from jaraco.functools 3.3
6def method_cache(method, cache_wrapper=None):
7 """
8 Wrap lru_cache to support storing the cache data in the object instances.
10 Abstracts the common paradigm where the method explicitly saves an
11 underscore-prefixed protected property on first call and returns that
12 subsequently.
14 >>> class MyClass:
15 ... calls = 0
16 ...
17 ... @method_cache
18 ... def method(self, value):
19 ... self.calls += 1
20 ... return value
22 >>> a = MyClass()
23 >>> a.method(3)
24 3
25 >>> for x in range(75):
26 ... res = a.method(x)
27 >>> a.calls
28 75
30 Note that the apparent behavior will be exactly like that of lru_cache
31 except that the cache is stored on each instance, so values in one
32 instance will not flush values from another, and when an instance is
33 deleted, so are the cached values for that instance.
35 >>> b = MyClass()
36 >>> for x in range(35):
37 ... res = b.method(x)
38 >>> b.calls
39 35
40 >>> a.method(0)
41 0
42 >>> a.calls
43 75
45 Note that if method had been decorated with ``functools.lru_cache()``,
46 a.calls would have been 76 (due to the cached value of 0 having been
47 flushed by the 'b' instance).
49 Clear the cache with ``.cache_clear()``
51 >>> a.method.cache_clear()
53 Same for a method that hasn't yet been called.
55 >>> c = MyClass()
56 >>> c.method.cache_clear()
58 Another cache wrapper may be supplied:
60 >>> cache = functools.lru_cache(maxsize=2)
61 >>> MyClass.method2 = method_cache(lambda self: 3, cache_wrapper=cache)
62 >>> a = MyClass()
63 >>> a.method2()
64 3
66 Caution - do not subsequently wrap the method with another decorator, such
67 as ``@property``, which changes the semantics of the function.
69 See also
70 http://code.activestate.com/recipes/577452-a-memoize-decorator-for-instance-methods/
71 for another implementation and additional justification.
72 """
73 cache_wrapper = cache_wrapper or functools.lru_cache()
75 def wrapper(self, *args, **kwargs):
76 # it's the first call, replace the method with a cached, bound method
77 bound_method = types.MethodType(method, self)
78 cached_method = cache_wrapper(bound_method)
79 setattr(self, method.__name__, cached_method)
80 return cached_method(*args, **kwargs)
82 # Support cache clear even before cache has been created.
83 wrapper.cache_clear = lambda: None
85 return wrapper
88# From jaraco.functools 3.3
89def pass_none(func):
90 """
91 Wrap func so it's not called if its first param is None
93 >>> print_text = pass_none(print)
94 >>> print_text('text')
95 text
96 >>> print_text(None)
97 """
99 @functools.wraps(func)
100 def wrapper(param, *args, **kwargs):
101 if param is not None:
102 return func(param, *args, **kwargs)
104 return wrapper