Home > Article > Backend Development > Lazy evaluation of Python class attributes
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 calculation property is to improve performance
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 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 every time it is calculated in area(), and after calling c.area twice in a row, "Computing area" will be printed. " was printed only once. 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.