python学习笔记------类的魔术方法与format

类的魔术方法

class OpenFile(object):
    def __init__(self, filename, mode):
        print("file is opening.......")
        self.f = open(filename, mode)
    def closed(self):
        return  self.f.closed
    def __del__(self):
        # del f1
        # 程序执行结束....
        self.f.close()
        print("file is deleteing.....", self.f.closed)


f = OpenFile('/etc/passwd', 'r')
print(f.closed())

# del f
# print(f.closed())

file is opening.......
False
file is deleteing..... True

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class Student(object):
    def __init__(self, name, age, score):
        self.name = name
        self.age = age
        self.score = score
        print("student is create")

    def __str__(self):
        return "Student:<%s,%s,%s>" %(self.name, self.age, self.score)
    def __del__(self):
        print("student is delete")

s1 = Student("westos", 19, 100)
print(s1)

student is create
Student:<westos,19,100>
student is delete

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私有属性和变量

以双下划线开头的属性名或者方法名，外部是不可以访问的；
子类也不能直接使用父类的私有属性和私有方法；

eg：

# 子类也不能直接使用父类的私有属性和私有方法;
class Student(object):
    def __init__(self, name, age, score):
        self.name = name
        self.age = age
        # 以双下划线开头的属性名或者方法名， 外部是不可以访问的;
        self.__score = score
    def set_score(self, value):
        if 0<=value<=150:
            self.__score = value

    def __get_level(self):
        if 90<self.__score<=100:
            return "%s,%s,A" %(self.name,self.age)
        elif 80<self.__score<=90:
            return  "%s,%s,B" %(self.name,self.age)
        else:
            return  "%s,%s,C" %(self.name,self.age)


class MathStudent(Student):
    def get_score(self):
        print(self.__score)



s1 = Student("westos", 18, 100)
print(s1.name)

s2 = MathStudent("helo",10,90)
# print(s2.__score)
# s1.__get_level()
# print(s1.__score)
s1.name = "fentiao"
print(s1.name)
s1.score = 150
print(s1.score)

类的多继承算法

class D:
    # pass
    def test(self):
        print("D test")
class C(D):
    pass
    # def test(self):
    #     print("C test")
class B(D):
    pass
    # def test(self):
    #     print("B test")
class A(B,C):
    pass
    # def test(self):
    #     print("A test")

a = A()
a.test()

format

自定义字符串的格式化

# format() 函数和字符串方法使得一个对象能支持自定义的格式化;

# 为了自定义字符串的格式化,我们需要在类上面定义 __format__()方法:


formats = {
    'ymd':"{d.year}-{d.month}-{d.day}",
    'dmy':"{d.day}/{d.month}/{d.year}"
}

class Date(object):
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    def __format__(self, format_spec):   # 'dmy'
        if not format_spec:
            format_spec = 'ymd'
        fmt = formats[format_spec]

        return fmt.format(d=self)


d = Date('2018', '5', '20')
print(format(d, 'ymd'))   # 2018-5-20
print(format(d, 'dmy'))   # 20/5/2018
print(format(d))   # 2018-5-20

format格式转换：

字符传format方法的使用

format是python2.6新增的一个格式化字符串的方法，
相对于老版的%格式方法，它有很多优点。

        1.不需要理会数据类型的问题，在%方法中%s只能替代字符串类型

        2.单个参数可以多次输出，参数顺序可以不相同

        3.填充方式十分灵活，对齐方式十分强大

        4.官方推荐用的方式，%方式将会在后面的版本被淘汰


# 1.通过位置来填充字符串
print("hello %s" % ('world'))
# print("hello %s" %((1,2,3)))


print("hello {0}".format((1, 2, 3, 4)))
print("hello {0} {1} {0} {1}".format((1, 2, 3, 4), "python"))
print("hello {0:.3f}".format(1.8989))

# 2.通过key来填充

print("max:{max} min:{min}".format(min=10, max=100))

# 3.通过下标/index填充

point = (3,4)
print("x:{0[0]}, y:{0[1]}".format(point))

# 4.通过字典的key

d = {'max':100.7849758475976, 'min':10.4756895769857985}
print("max:{max:.2f} min:{min:.3f}".format(**d))

# 5. oop对象进行操作
class Book(object):
    def __init__(self, name, author, state, bookIndex):
        self.name = name
        self.author = author
        # 0:借出 1：未借出
        self.state = state
        self.bookIndex = bookIndex

    # 打印对象时自动调用;str(对象)
    def __str__(self):
        return "书名:{0.name} 状态:{0.state}".format(self)
        # return "书名:{d.name} 状态:{d.state}".format(d=self)

b = Book("java", 'aa', 1, 'Index')
print(b)

hello world
hello (1, 2, 3, 4)
hello (1, 2, 3, 4) python (1, 2, 3, 4) python
hello 1.899
max:100 min:10
x:3, y:4
max:100.78 min:10.476
书名:java 状态:1

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