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The so-called delayed calculation of class attributes is to define the attributes of the class as a property, which will only be calculated when accessed, and once accessed, the result will be cached and does not need to be calculated every time.
Advantages
The main purpose of constructing a lazy calculated property is to improve performance
Achieved
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 value
import math
class 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
Instructions
Defines a lazy calculation decorator class LazyProperty. Circle is a class used for testing. The Circle class has three attributes: radius, area, and perimeter. The properties of area and perimeter are decorated by LazyProperty. Let’s try the magic of LazyProperty:
>>> c = Circle(2) >>> print c.area Computing area 12.5663706144 >>> print c.area 12.5663706144
"Computing area" will be printed once for each calculation in area(), but "Computing area" will only be printed once after calling c.area twice. This is due to LazyProperty, as long as it is called once, it will not be counted again no matter how many subsequent calls are made.
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