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)

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

https://wiki.python.org/moin/PythonDecoratorLibrary#Memoize

FunctoolsCache

https://docs.python.org/3/library/functools.html

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)

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):
>>>     @ub.memoize_method
>>>     def foo_memo(self, key):
>>>         "Wrapped foo_memo docstr"
>>>         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
>>> assert self.foo_memo.__doc__ == 'Wrapped foo_memo docstr'
>>> assert self.foo_memo.__name__ == 'foo_memo'

ubelt.util_memoize.memoize_property(fget)

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

estebistec_memoize

https://github.com/estebistec/python-memoized-property

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