Delay computation of Python class attributes _python

The delay calculation of the class attribute is to define the attribute of the class as a property, only when it is accessed, and once accessed, the result will be cached and not calculated every time.

Advantages

The primary purpose of constructing a deferred computed property is to improve performance

Realize

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

An adorner class lazyproperty is defined for a delay calculation. Circle is the class that is used for testing, and the Circle class has three property radii (RADIUS), size (area), perimeter (perimeter). The area and perimeter properties are decorated by lazyproperty, and try the magic of Lazyproperty:

>>> C = Circle (2)
>>> print C.area
Computing area
12.5663706144
>>> Print C.area
12.5663706144

"Computing area" is printed once per calculation in area (), and "Computing area" is only printed once after two consecutive c.area calls. This benefits from Lazyproperty, which, once invoked once, will not be repeated regardless of the number of subsequent calls.

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