无聊。。。。。

Posted 2020-10-27 不会起名字

# __class__表示当前操作的对象是什么
# 1、如何让b的对象实现a的shou方法
# class A:
#     def show(self):
#         print("A-show")
#
# class B(A):
#     def show(self):
#         print("B-show")
#
# # obj = B()
# # # print(obj.__class__)
# # obj.__class__=A
# # obj.show()



#  2、这段代码怎么才能运行，（为了让对象的实例可以被直接调用，实现call方法）
# class A(object):
#     def __init__(self,a,b):
#         self.__a = a
#         self.__b = b
#     def myprint(self):
#         print("a=",self.__a,"b=",self.__b)
#     # def __call__(self, num):
#     #     print("call:",num + self.__a)
#
# # a = A(10,20)
# # a.myprint()
# #
# # a(100)


# 3、# __new__,和 __init__
# class B:
#     def fn(self):
#         print("B-fn")
#     def __init__(self):
#         print("B-init")
#
# class A:
#     def fn(self):
#         print("A-fn")
#     def __new__(cls, a):
#         print("new",a)
#         if a > 10:
#             return super(A,cls).__new__(cls)
#         return B
#     def __init__(self,a):
#         print("init",a)
#
# # a1 = A(5)
# # a1.fn(1)
# # a2 = A(20)
# # a2.fn()


# 4、list or dict
# ls = [1,2,3,4]
# list1 = [i for i in ls if i>2]
# print(list1)         #[3, 4]
#
# list2 = [i*2 for i in ls if i>2]
# print(list2)         #[6, 8]
#
# dic1 = {x:x**2 for x in (2,4,6)}
# print(dic1)         #{2: 4, 4: 16, 6: 36}
#
# dic2 = {x:‘item‘+str(x**2) for x in (2,4,6)}
# print(dic2)        #{2: ‘item4‘, 4: ‘item16‘, 6: ‘item36‘}
#
# set1 = {x for x in ‘hello world‘ if x not in ‘low level‘}
# print(set1)        #{‘d‘, ‘h‘, ‘r‘}


# 6、全局or局部
# num = 9
# def f1():
#     global num
#     num = 20
#     # print(num)
# def f2():
#     print(num)
# f2()
# f1()
# f2()


# class A:
#     def __init__(self,a,b):
#         self.a1 = a
#         self.b1 = b
#         print("init")
#     def mydefault(self):
#         print("default")
#     def __getattr__(self, item):
#         print("getattr")
#         return self.mydefault()
#
# a1 = A(10,20)
# a1.fn1()



# __all__ = ["mod2","mod1"]   #  卸载iniit里，只导入这两个模块
#
# def mulby(num):
#     def gn(val):
#         return num * val
#     return gn
#
# zw = mulby(7)
# print(zw(6))


def strtest(num):
    str1 = "first"
    for i in range(num):
        str1 +="x"
    return str1
# python的str是个不可变对象，每次迭代，都会生成新的str对象来存储新的字符串，num越大，创建的str对象越多，内存消耗越大。


# numbers = [x*x for x in range(20) if x % 3 == 0]
# numbers = {x * x for x in range(0, 20) if x % 3 == 0}
# numbers = {x: x * x for x in range(0, 20) if x % 3 == 0}

a = "I love python"
reverse_a = a[::-1]
print(reverse_a)

cities = ["beijin","tianjin","shenzhegn"]
for index,city in enumerate(cities,1):
    print(index,":",city)