56 lines
1.1 KiB
Python
56 lines
1.1 KiB
Python
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#!/usr/bin/env python
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# -*- encoding: utf-8 -*-
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"""
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Topic: 延迟属性
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Desc :
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"""
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import math
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class lazyproperty:
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def __init__(self, func):
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self.func = func
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def __get__(self, instance, cls):
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if instance is None:
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return self
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else:
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value = self.func(instance)
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setattr(instance, self.func.__name__, value)
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return value
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class Circle:
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def __init__(self, radius):
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self.radius = radius
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@lazyproperty
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def area(self):
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print('Computing area')
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return math.pi * self.radius ** 2
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@lazyproperty
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def perimeter(self):
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print('Computing perimeter')
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return 2 * math.pi * self.radius
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c = Circle(4.0)
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print(vars(c))
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print(c.area)
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print(vars(c))
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del c.area
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print(vars(c))
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print(c.area)
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def lazyproperty2(func):
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name = '_lazy_' + func.__name__
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@property
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def lazy(self):
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if hasattr(self, name):
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return getattr(self, name)
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else:
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value = func(self)
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setattr(self, name, value)
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return value
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return lazy
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