Python-----类的基本操作

最新推荐文章于 2024-08-12 15:42:30 发布

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本文介绍了Python中的类操作，包括魔术方法如构造函数`__init__`和解析函数，对象的`str`与`repr`方法，以及字符串的格式化。还展示了图书管理系统的例子，探讨了面向对象编程中类的属性和方法，如`__str__`方法。同时，讲解了使用下标和索引值填充字符串，以及如何通过`**d`传递字典参数。最后，提到了类方法和静态方法的概念。

1.魔术方法之构造函数与解析函数

class People(object):
    实例化对象时自动执行
    def __init__(self, name, age):
         把属性和对象名绑定在一起， 便于访问对象的属性.
        self.name = name
        self.age = age
        print("创建对象成功.......")
     析构函数, 当你删除对象时， 自动调用的方法。
       del 对象名或者程序执行结束之后
    def __del__(self):
        print("删除对象成功.......")
if __name__ == '__main__':
    创建对象
    p1 = People('fentiao', 12)
del p1

2.对象str与repr方法

class People(object):
     实例化对象时自动执行
    def __init__(self, name, age):
         把属性和对象名绑定在一起， 便于访问对象的属性.
        self.name = name
        self.age = age
        print("创建对象成功.......")
      析构函数, 当你删除对象时， 自动调用的方法。
       del 对象名或者程序执行结束之后
    def __del__(self):
        print("删除对象成功.......")
      __str__和__repr__都是对对象的字符串显示， 使用场景不同.
     如果没有__str__的时候， 自动调用__repr__方法的内容.
    def __str__(self):
        print(‘对象名‘)  
        print(str(‘对象名‘))
        print('People(%s, %d)' %(self.name, self.age))
        return  'People(%s, %d)' %(self.name, self.age)
    def __repr__(self):
        print(repr(‘对象名‘))  或者交互式环境中直接： 对象名
        return  "People(%s)" %(self.name)
    def __hello(self):
        print("hello")
    def world(self):
        self.__hello()
if __name__ == '__main__':
    创建对象
    p1 = People('fentiao', 12)
    print(p1)
    print(p1.__str__())
    p1.world()
    print(str(p1))
    print(repr(p1))

3.图书管理系统

假设每本书只有一本
class Book(object):
    def __init__(self, name, author, state, bookIndex):
        self.name = name
        self.author = author
         0：'已借出' 1:'未借出'
        self.state = state
        self.bookIndex = bookIndex

    def __str__(self):
        return 'Book(%s, %d)' % (self.name, self.state)
class BookManage(object):
     存放所有书籍信息, 列表里面存放的是Book对象
    books = []
    def start(self):
        """图书管理系统初始化数据"""
        self.books.append(Book('python', 'Guido', 1, 'IN23445'))
        self.books.append(Book('java', 'Guido1', 1, 'IN23445'))
        self.books.append(Book('C++', 'Guido2', 1, 'IN23445'))
        print("初始化数据成功!")
    def Menu(self):
        """图书管理菜单栏"""
        while True:
            print("""
                        图书管理操作

            1). 添加书籍
            2). 删除数据
            3). 查询书籍

            4). 退出
            """)
            choice = input("请输入你的选择:")
            if choice == '1':
                self.addBook()
            elif choice == '2':
                self.delBook()
            elif choice == '3':
                self.isBookExist('python')
            elif choice == '4':
                exit()
            else:
                print("请输入正确的选择!")
    def addBook(self):
        print("添加书籍".center(0, '*'))
        name = input("书籍名称:")
        bObj = self.isBookExist(name)
        if bObj:
            print("书籍%s已经存在" % (bObj.name))
        else:
            self.books.append(Book(name, input("作者:"), 1, input("存放位置:")))
            print("书籍%s添加成功" % (name))
    def delBook(self):
        pass
    def borrowBook(self):
        pass

  def isBookExist(self, name):
        for book in self.books:
            if book.name==name:
                return book
            else:
                return False
bManager=BookManage()
bManager.start()
bManager.Menu()

4.字符串的方法

print("name:%s, age:%d, scores:%s" % ('westos', 10, dict(a=1, b=2)))
print("name:%s, age:%d, scores:%s" % ('westos', 10, (1, 2)))
print("name:%s, age:%d, name:%s" % ('westos', 10, 'westos'))

通过位置填充字符串
print("name:{0}, age:{1}, scores:{2}".format('westos', 10, [100, 100, 100]))
print("name:{0}, age:{1}, scores:{0}".format('westos', 10))
print("name:{0}, id:{1:.3f}, scores:{0}".format('westos', 19.2332435))

通过key值填充字符串
d = {'max': 100, 'min': 10}
print("MAX: {max}, MIN:{min}".format(max=100, min=10))
print("MAX: {max}, MIN:{min}".format(**d))

通过下标或者索引值填充
point = (3,4)
print("x:{0[0]}, y:{0[1]}".format(point))

面向对象操作
class Book(object):
    def __init__(self, name, author, state, bookIndex):
        self.name = name
        self.author = author
        0：'已借出' 1:'未借出'
        self.state = state
        self.bookIndex = bookIndex

def __str__(self):
return 'Book(%s, %d)' %(self.name, self.state)
b = Book('python', 'guido', 1, 'IND444')
print("name:{b.name}, state:{b.state}, author:{b.state}".format(b=b))
print("name:{0.name}, state:{0.state}, author:{0.state}".format(b))

运行结果：

5.format魔术方法

class Date(object):
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day
    # format方法: format(对象名)时自动调用
    def __format__(self, format_spec=None):
        if not format_spec:
            return  "%s-%s-%s" %(self.year, self.month, self.day)
        else:
            if format_spec == 'ymd':
                return  "%s-%s-%s" %(self.year, self.month, self.day)
            elif format_spec == 'dmy':
                return   "%s/%s/%s" %(self.day, self.month, self.year)
            else:
                return  "error format"
d = Date(2019, 8, 25)
print(format(d))
print(format(d, 'ymd'))
print(format(d, 'dmy'))
print(d.__format__('ymd'))
print(format(d, 'ymd'))
‘ymd’ ===> ‘2019-8-25’
‘mdy’ ===> '8/25/2019'

运行结果：

6.类内部装饰器

class Book(object):
    def __init__(self, name, author, state, bookIndex):
        self.name = name
        self.author = author
        0：'已借出' 1:'未借出'
        self.__state = state
        self.bookIndex = bookIndex
    def get_state(self):
        if self.__state == 0:
            return  '已借出'
        elif self.__state == 1:
            return  '未借出'
        else:
            return  "状态异常"
    def set_state(self, value):
        # if value == 0 or value == 1:
        if value in (0,1):
            更新书籍的状态
            self.__state = value
    def del_state(self):
        print("is deleteing......")
    def __str__(self):
        return  'Book(%s, %d)' %(self.name, self.__state)

    state = property(fget=get_state, fset=set_state, fdel=del_state)
b = Book('python', 'guido', 1, 'chddf')
print(b.state)
运行结果
1). 书籍的状态可以人以改变， 并不能限制只能为0或者1；
2). 书籍状态如何友好的显示?
b.state = 10
print(b.state)
3). 问题解决, 但是调用比较复杂, 可读性不高.
print(b.get_state())
print(b.set_state(10))
print(b.get_state())
4).
print(b.state)
b.state = 0
print(b.state)
del  b.state

7.类的切片与索引

str, list
li = [1,2,3,4,5,6]
__getitem__:  li[0]
__setitem__: li[0] = 10
__delitem__: del li[0]
class Student(object):
    def __init__(self, name, scores):
        self.name = name
        self.scores = scores
    支持索引; s[index]
    def __getitem__(self, index):
        print("获取索引对应的value值")
        return  self.scores[index]
    s[索引] = 修改的值
    def __setitem__(self, index, value):
        self.scores[index] = value
    del s[索引]
    def __delitem__(self, index):
        del self.scores[index]
    def hello(self):
        return  "hello"
s = Student('westos', [101, 100, 100])
2.index
print(s[0])
print(s[1])
print(s[2])
0, 200
s[0] = 200
print(s[0])
print(s.scores)
del s[0]
print(s.scores)

运行结果：

class Student(object):
    def __init__(self, name, scores):
        self.name = name
        self.scores = scores
    支持索引; s[key]
    def __getitem__(self, key):
        print("获取索引对应的value值")
        return  self.__dict__[key]
    s[key] = 修改的值
    def __setitem__(self, key, value):
        self.__dict__[key] = value
    del s[key]
    def __delitem__(self, key):
        del self.__dict__[key]
    def hello(self):
        return  "hello"
s = Student('westos', [101, 100, 100])
key获取value值
可以获取所有的属性为key值, 以及对应的value值, 并封装为一个字典返回.
print(s.__dict__)
print(s['name'])
print(s['scores'])
s['name'] = 'westo1'
print(s['name'])
del s['name']
print(s['name'])

str, list
li = [1,2,3,4,5,6]
__getitem__:  li[0]   === __getslice__
__setitem__: li[0] = 10  == __setslice__
__delitem__: del li[0]   == __delslice__
class Student(object):
    def __init__(self, name, scores):
        self.name = name
        self.scores = scores
    def __getitem__(self, key):
        return self.scores[key]
    def __setitem__(self, key, value):
        self.scores[key] = value
    def __delitem__(self, key):
        del self.scores[key]
对于切片的操作
s = Student('westos', [101, 90, 101])
print(s[1:3])
s[1:3] = [0,0]
print(s[:])
del s[:-1]
print(s[:])
print(s[0])

8.重复，连接与成员操作符的实现

from collections import Iterable
class Student(object):
    def __init__(self, name, scores):
        self.name = name
        self.scores = scores
        self.power = 100
    obj1 + obj2
    def __add__(self, other):
        更新self对象的power属性值；
        self.power =  self.power + other.power
        return  self
    obj1 * 3
    def __mul__(self, other):
        *的效果是， 能量*power
        return  self.power * other
    成员操作符； item in obj1
    def __contains__(self, item):
        return  item in self.scores
    可以for循环迭代
    def __iter__(self):        
        iter([1,2,3,4,5])
        <list_iterator object at 0x7f6e1f51ffd0>
        iter({1,2,3,4,5})
        <set_iterator object at 0x7f6e1f567318>
        迭代返回的是成绩
        return  iter(self.scores)
    def __repr__(self):
        return  "Student:%s,%s" %(self.name, self.power)
print("hello " + "world")
print([1,2,3] + [3,4,5])
s1 = Student('westos1', [101,100,100])
s2 = Student('westos2', [100,100,100])
s3 = Student('westos3', [100,100,100])
运行结果：

连接的实现;
"hello" + "world" + "hwllo"
print(s1 + s2 + s3)
a = 1 ; a+=1 a=2
str = "h"; str+='e' str=''he
s1 += s2
print(s1)
重复:
a = 3; 
print(a*3)
s = 'a'; 
print(s*3)
li = [1,2,3]; 
print(li*3)
print(s1*3)
成员操作符
print(s1.scores)
print(200 in s1)
print(100 in s1)
print(200 not in s1)
print(100 not in s1)

for循环迭代
for i in s1:
    print(i)
print(isinstance(s1, Iterable))

9.比较大小计算长度

class Student(object):
    def __init__(self, name, scores, power):
        self.name = name
        self.scores = scores
        self.power = power

    def __add__(self, other):
        更新self对象的power属性值；
        self.power =  self.power + other.power
        return  self
    obj1 > obj2
    def __gt__(self, other):
        return  self.power > other.power
    obj >= obj2
    __ge__ = lambda  self, other: self.power >= other.power
    obj1 ==  obj2
    def __eq__(self, other):
        return self.power ==  other.power
    def __ne__(self, other):
        return  self.power !=  other.power
        return  not self.__eq__(other)
    def __repr__(self):
        return  "Student:%s,%s" %(self.name, self.power)
    def __len__(self):
        return  len(self.scores)
s1 = Student('westos1', [101,100,100], 100)
s2 = Student('westos2', [100,100,100], 101)
s3 = Student('westos3', [100,100,100], 80)
print(s1+s2)
print(s1 > s2 > s3)
print(s1>=s2)
print(s1<s2)
print(s1 == s2)
print(s1 != s2)
print(len(s1))

运行结果

10.call方法

实现一个单例模式
from django.core.paginator import Page
class Student(object):
    def __init__(self, name, scores, power):
        self.name = name
        self.scores = scores
        self.power = power
    def __call__(self, *args, **kwargs):
        return "对象被调用......"
    class: 实例化对象之前执行
    def __new__(cls, *args, **kwargs):
        判断是否obj对象是否已经被创建, 如果没有被创建， 则创建，
        if not hasattr(cls, 'obj'):
            cls.obj = object.__new__(cls)
        如果已经创建成功，则返回创建好的对象
        return  cls.obj
s1 = Student('westos1', [101,100,100], 100)
s2 = Student('westos1', [101,100,100], 100)
print(s1)
print(s2)

运行结果：

11.类方法与静态方法

class Date(object):
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day =  day
    echo普通方法, 默认情况下会传递对象给echo
    def echo(self):
        return  "%s %s %s" %(self.year, self.month, self.day)

    默认传递类本身给这个方法;
    @classmethod
    def as_string(cls, s):
        print(cls)
        month, day, year = s.split('/')
        d = cls(year, month, day)
        return d
     默认python解释器不会传递任何参数
    @staticmethod
    def is_vaild(s):
        批量将年月日转换成整形(列表生成式， map)
        month, day, year = s.split('/')
        month, day, year = [int(i) for i in s.split('/')]
        month, day, year = map(int, s.split('/'))
        return 0 < month <= 12 and 0 < day <= 31 and 1 < year < 9999
d = Date(2018, 10, 10)
d.echo()
s = '10/10/2018'
print(as_string('12/10/2019').echo())
print(Date.as_string(s).echo())
s = '10/10/2018'
print(Date.is_vaild(s))
d = Date(2018, 10, 10)
print(d.is_vaild('13/10/2019'))
from datetime import  date
类方法的官方使用案例: from datetime import date

    @classmethod
    def fromtimestamp(cls, t):
        "Construct a date from a POSIX timestamp (like time.time())."
        y, m, d, hh, mm, ss, weekday, jday, dst = _time.localtime(t)
        return cls(y, m, d)
    @classmethod
    def today(cls):
        "Construct a date from time.time()."
        t = _time.time()
        return cls.fromtimestamp(t)
类属性的官方使用案例: 显示年月日， 但是不能任意修改年月日
    Read-only field accessors
    @property
    def year(self):
        return self._year
    @property
    def month(self):
        
        return self._month
    @property
    def day(self):
        return self._day
from datetime import  date

12.with语句

class MyOpen(object):
    def __init__(self, filename, mode='r'):
        self._name = filename
        self._mode = mode
    当with语句开始运行的时候，执行什么方法;
    def __enter__(self):
        self.f = open(self._name, self._mode)
        return  self.f
    当with语句执行结束之后出发某个方法的运行;
    def __exit__(self, exc_type, exc_val, exc_tb):
        self.f.close()
    @property
    def name(self):
        return  self._name
    @property
    def mode(self):
        return  self._mode
with MyOpen('/etc/passwd')   as f:
    print(f.closed)
    print(f.read(5))
print(f.closed)
with open('/etc/passwd') as f: