ubelt.util_memoize module¶
This module exposes decorators for in-memory caching of functional results. This is particularly useful when prototyping dynamic programming algorithms.
Either memoize()
, memoize_method()
, and memoize_property()
should be used depending on what type of function is being wrapped. The
following example demonstrates this.
In Python 3.8+ memoize()
and memoize_method()
work similarly to the
standard library functools.cache()
and functools.memoize_method()
,
but the ubelt version makes use of ubelt.util_hash.hash_data()
, which
is slower, but handles inputs containing mutable containers.
Example
>>> import ubelt as ub
>>> # Memoize a function, the args are hashed
>>> @ub.memoize
>>> def func(a, b):
>>> return a + b
>>> #
>>> class MyClass:
>>> # Memoize a class method, the args are hashed
>>> @ub.memoize_method
>>> def my_method(self, a, b):
>>> return a + b
>>> #
>>> # Memoize a property: there can be no args,
>>> @ub.memoize_property
>>> @property
>>> def my_property1(self):
>>> return 4
>>> #
>>> # The property decorator is optional
>>> def my_property2(self):
>>> return 5
>>> #
>>> func(1, 2)
>>> func(1, 2)
>>> self = MyClass()
>>> self.my_method(1, 2)
>>> self.my_method(1, 2)
>>> self.my_property1
>>> self.my_property1
>>> self.my_property2
>>> self.my_property2
- ubelt.util_memoize.memoize(func)[source]¶
memoization decorator that respects args and kwargs
In Python 3.9. The
functools
introduces the cache method, which is currently faster than memoize for simple functions [FunctoolsCache]. However, memoize can handle more general non-natively hashable inputs.- Parameters
func (Callable) – live python function
- Returns
memoized wrapper
- Return type
Callable
References
- WikiMemoize
- FunctoolsCache
Example
>>> import ubelt as ub >>> closure = {'a': 'b', 'c': 'd'} >>> incr = [0] >>> def foo(key): >>> value = closure[key] >>> incr[0] += 1 >>> return value >>> foo_memo = ub.memoize(foo) >>> assert foo('a') == 'b' and foo('c') == 'd' >>> assert incr[0] == 2 >>> print('Call memoized version') >>> assert foo_memo('a') == 'b' and foo_memo('c') == 'd' >>> assert incr[0] == 4 >>> assert foo_memo('a') == 'b' and foo_memo('c') == 'd' >>> print('Counter should no longer increase') >>> assert incr[0] == 4 >>> print('Closure changes result without memoization') >>> closure = {'a': 0, 'c': 1} >>> assert foo('a') == 0 and foo('c') == 1 >>> assert incr[0] == 6 >>> assert foo_memo('a') == 'b' and foo_memo('c') == 'd'
- class ubelt.util_memoize.memoize_method(func)[source]¶
Bases:
object
memoization decorator for a method that respects args and kwargs
References
- ActiveState_Miller_2010
http://code.activestate.com/recipes/577452-a-memoize-decorator-for-instance-methods
Example
>>> import ubelt as ub >>> closure = {'a': 'b', 'c': 'd'} >>> incr = [0] >>> class Foo(object): >>> @memoize_method >>> def foo_memo(self, key): >>> value = closure[key] >>> incr[0] += 1 >>> return value >>> def foo(self, key): >>> value = closure[key] >>> incr[0] += 1 >>> return value >>> self = Foo() >>> assert self.foo('a') == 'b' and self.foo('c') == 'd' >>> assert incr[0] == 2 >>> print('Call memoized version') >>> assert self.foo_memo('a') == 'b' and self.foo_memo('c') == 'd' >>> assert incr[0] == 4 >>> assert self.foo_memo('a') == 'b' and self.foo_memo('c') == 'd' >>> print('Counter should no longer increase') >>> assert incr[0] == 4 >>> print('Closure changes result without memoization') >>> closure = {'a': 0, 'c': 1} >>> assert self.foo('a') == 0 and self.foo('c') == 1 >>> assert incr[0] == 6 >>> assert self.foo_memo('a') == 'b' and self.foo_memo('c') == 'd' >>> print('Constructing a new object should get a new cache') >>> self2 = Foo() >>> self2.foo_memo('a') >>> assert incr[0] == 7 >>> self2.foo_memo('a') >>> assert incr[0] == 7
- ubelt.util_memoize.memoize_property(fget)[source]¶
Return a property attribute for new-style classes that only calls its getter on the first access. The result is stored and on subsequent accesses is returned, preventing the need to call the getter any more.
This decorator can either be used by itself or by decorating another property. In either case the method will always become a property.
Note
implementation is a modified version of [estebistec_memoize].
References
Example
>>> import ubelt as ub >>> class C(object): ... load_name_count = 0 ... @ub.memoize_property ... def name(self): ... "name's docstring" ... self.load_name_count += 1 ... return "the name" ... @ub.memoize_property ... @property ... def another_name(self): ... "name's docstring" ... self.load_name_count += 1 ... return "the name" >>> c = C() >>> c.load_name_count 0 >>> c.name 'the name' >>> c.load_name_count 1 >>> c.name 'the name' >>> c.load_name_count 1 >>> c.another_name