Python特殊方法与类的定制 --面向对象编程

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1、控制类中返回字符串的方法：__ str __

# coding:utf8
class CustomClass:
    def __init__(self, name):
        self.name = name

    # 控制类中返回字符串的方法
    def __str__(self):
        print('First executing the method，then executing the print operation！')
        return 'Hello ' + self.name + '!'


print(CustomClass('Thanlon'))

2、使用 @property简化get和set方法

# coding:utf8
import traceback


class Stu:
    @property
    def score(self):
        return self._score

    @score.setter
    def score(self, value):
        if not isinstance(value, int):
            raise ValueError('not int')
        elif value < 0 or value > 100:
            raise ValueError('not between 0 and 100')
        self._score = value

    @property
    def double_score(self):
        return self._score * 2


stu = Stu()
stu.score = 99
print(stu.score)
# try:
#     stu.score = '100'
# except ValueError:
#     traceback.print_exc()
# except Exception:
#     traceback.print_exc()
# try:
#     stu.score = -1
# except ValueError:
#     traceback.print_exc()
# except Exception:
#     traceback.print_exc()

print(stu.double_score)
#实现只读属性
# setter will be failed,double_score,property is only read
try:
    stu.double_score = 100
except AttributeError:
    traceback.print_exc()  # 报错信息：AttributeError: can't set attribute

例：利用@property给Screen对象加上可读可写的width和height属性、以及一个只读属性resolution。

class Screen:
    @property
    def width(self):
        return self._width

    @width.setter
    def width(self, value):
        self._width = value

    @property
    def height(self):
        return self._height

    @height.setter
    def height(self, value):
        self._height = value

    @property
    def resolution(self):
        return self._resolution