Use lazy initialization method to improve Python performance

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, without having to do it every time All calculated. The main purpose of constructing a delayed calculation property is to improve performance
property
Before getting to the point, let’s understand the usage of property. Property can convert property access into method invocation.

class Circle(object): 
 def init(self, radius): 
  self.radius = radius 
  
 @property
 def area(self): 
  return 3.14 * self.radius ** 2
  
c = Circle(4) 
print c.radius 
print c.area

It can be seen that although area is defined as a method, after adding @property, c.area can be directly executed and accessed as a property.
Now the question is coming. Every time c.area is called, it will be calculated once. It is a waste of CPU. How can we only calculate it once? This is lazy property
Code 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 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

Description
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

In area(), "Computing area" will be printed once every time it is calculated, and it will be called twice in succession. "Computing area" is only printed once after c.area. 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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