Delay initialization for Python Performance Improvement and python Performance Improvement

Delay initialization for Python Performance Improvement and python Performance Improvement

The so-called latency Calculation of class attributes defines the class attributes as a property, which is calculated only when accessed. Once accessed, the results will be cached, you do not need to calculate it every time. The main purpose of constructing a delayed computing attribute is to improve performance.

Property

Before proceeding to the topic, let's take a look at the usage of property. property can convert access to properties into method calls.

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, although area is defined as a method, after adding @ property, you can directly execute c. area as a property access.

Now the question is, every call to c. area will be calculated once, which is a waste of cpu. How can we calculate only 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 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.