Python class attribute delay calculation

The delay calculation of Python class attributes the so-called class attribute delay calculation is to define the class attribute as a property, which is only calculated during access, and once accessed, the results will be cached and do not need to be calculated every time.

Advantages

The main purpose of constructing a delayed computing attribute is to improve performance.

Implementation

class LazyProperty(object):    def __init__(self, func):        self.func = func    def __get__(self, instance, owner):        if instance is None:            return self        else:            value = self.func(instance)            setattr(instance, self.func.__name__, value)            return valueimport mathclass Circle(object):    def __init__(self, radius):        self.radius = radius    @LazyProperty    def area(self):        print 'Computing area'        return math.pi * self.radius ** 2    @LazyProperty    def perimeter(self):        print 'Computing perimeter'        return 2 * math.pi * self.radius

Description

Defines a LazyProperty class for delayed computing. Circle is used for testing. The Circle class has three attributes: radius, area, and perimeter ). LazyProperty is decorated with the property of area and perimeter. let's try the magic of LazyProperty:

>>> c = Circle(2)>>> print c.areaComputing area12.5663706144>>> print c.area12.5663706144

"Computing area" is printed every time calculated in area (). after calling c. area twice in a row, "Computing area" is printed only once. This benefits from LazyProperty. after a call, no matter how many subsequent calls are called, the calculation will not be repeated.