Using Python delay initialization to improve performance examples

The so-called deferred computation of a class property is defined as a property of the class, which is evaluated only at the time of access, and once accessed, the result is cached and not calculated every time. The main purpose of constructing a deferred computed property is to improve performance

Property

Before we get to the point, we understand the use of the property, which transforms the access of the attribute into a call to the method.

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

As you can see, area is defined as a form of a method, but with @property, you can execute C.area directly as a property access.

Now the problem, every call C.area, will be calculated once, too wasted CPU, how to calculate only once? This is the 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 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

An adorner class Lazyproperty that defines a deferred calculation. Circle is the class used for testing, and the Circle class has three attribute radius (RADIUS), area, perimeter (perimeter). The area and perimeter properties are lazyproperty decorated, below to try Lazyproperty's Magic:

>>> C = Circle (2) >>> print c.areacomputing area12.5663706144>>> print c.area12.5663706144

Computing area is printed once per calculation in area (), and the "Computing area" is only printed once after a continuous call of two c.area. This is thanks to Lazyproperty, which, once invoked, does not repeat calculations regardless of the number of subsequent calls.