双下方法

双下方法:给源码程序员使用,咱们慎用 (以便你们更好的阅读源码)

len

class A(object):

def init(self,name):

self.name = name

print("触发了__init__")

def len(self): # len() 触发

print("走这里")

return len(self.name) # return len("alex") str中__len__

# 必须有返回值,返回值的类型必须是整型

a = A("alexqrqwr")

print(len(a))

str

a = "12345" # str这个类的实例

lst = [1,2,3,4,4,5,5,5,5] # list这个类的实例

print(len(a))

print(len(lst))

hash hash()触发

class A(object):

def init(self,name,age):

self.name = name

self.age = age

def hash(self): # hash()

hash({1,2,345}) # 可变数据类,不可数据类型

# 必须有返回值,返回值的类型必须是整型

a = A("meet",25)

print(hash(a))

str *** Django

class A:

def init(self,name,age,sex):

self.name = name

self.age = age

self.sex = sex

def str(self): # print 触发 str()

print(111)

return f"姓名:{self.name} 年龄:{self.age} 性别:{self.sex}"

# 必须有返回值,返回值的类型必须是字符串

a = A("meet",20,"男")

a1 = A("meet11",200,"男11")

str(a)

print(a)

print(a1)

a = A("meet",20,"男")

a1 = A("meet2",200,"女")

print(f"姓名:{a.name} 年龄:{a.age} 性别:{a.sex}") # "姓名:meet 年龄:20 性别:男"

print(f"姓名:{a1.name} 年龄:{a1.age} 性别:{a1.sex}") # "姓名:meet2 年龄:200 性别:女"

repr

class A:

def init(self):

pass

def repr(self): # print触发 %r

print(1111)

return "日魔"

def str(self): # str 优先级高于 repr 两个都存在就只执行str

return "宝元"

a = A()

print("%r"%(a))

call *** 面试题

class A:

def init(self):

pass

def call(self, *args, **kwargs): # 对象()时调用的__call__

print("走我")

print(*args, **kwargs)

a = A()

a()

eq # 等于

class A(object):

def init(self,name,age):

self.name = name

self.age = age

def eq(self, other): # a == a1

if self.name == other.name:

return True

else:

return False

a = A("meet",56)

a1 = A("meet",108)

print(a == a1)

del 析构方法

class A:

def init(self):

pass

def del(self): del 触发

print("删除时执行我")

a = A()

import time

time.sleep(5)

del a

a = 1

b = a

a = b

垃圾回收

# 80  5/s
# 引用计数
# 标记清除
# 分袋回收 袋一:10 2/h  袋二: 5/3 4h  袋三: 3 20h

new 单例模式(面试必问) # 工厂模式 等等

class A(object):

def init(self,name): # 初始化

self.name = name

print("我是__init__,先走我")

def new(cls, *args, **kwargs):

obj = object.new(A)

print("我在哪:",obj)

return obj # obj == init()

# print("我是__new__,先走我")

# return "啦啦啦"

a = A("meet")

print("我是谁:",a)

class A:

def init(self):

print(1111)

a = A()

print(a)

class A(object):

def init(self,name): # 初识化

self.name = name

# def __new__(cls, *args, **kwargs):
#     obj = object.__new__(A)   # 调用的是object类中的__new__ ,只有object类中的__new__能够创建空间
#     return obj   #本质: obj == __init__()     return __init__()  # 触发了__init__方法
#     # print("先执行的是我")
#     # return "宝元"

a = A("meet") # a是对象的内存地址

a1 = A("日魔") # a是对象的内存地址

a2 = A("朝阳") # a是对象的内存地址

print(a.name)

print(a1.name)

print(a2.name)

先执行__new__方法在执行__init__方法

class A:

__a = None #__a = 0x000001F346079FD0

def init(self,name,age):

self.name = name

self.age = age

def new(cls, *args, **kwargs):

if cls.__a is None:

obj = object.new(cls)

cls.__a = obj

return cls.__a

a = A("meet",123) # 0x000001F346079FD0

a1 = A("日魔",11)

print(a.name)

print(a1.name)

单例模式:不管你创建多少次,使用的都是同一个内存空间

模块的导入,手写的单例模式

实例化对象时发生的事

1.创建对象,并开辟对象空间 new

2.自动执行__init__方法

item 可以向操作字典一样操作实例方法

dic["键"] = 值

del dic["键"]

dic["键"]

class A:

def init(self,name,age):

self.name = name

self.age = age

def getitem(self, item):

print(self.dict)

print(self.dict[item]) # self.dict 获取的就是字典

def setitem(self, key, value):

self.dict[key] = value

def delitem(self, key):

del self.dict[key]

a = A("meet",58)

a["sex"] = "男"

a["sex"]

del a["sex"]

print(a.dict)

了解一下上下文

enter

exit

class my_open:

def init(self,file,mode="r",encoding="utf-8"):

self.file = file

self.mode = mode

self.encoding = encoding

def enter(self):

self.f = open(self.file,self.mode,encoding=self.encoding)

return self.f

def exit(self, exc_type, exc_val, exc_tb):

print(exc_type,exc_val,exc_tb) # 没有错误时就是None

self.f.close()

with my_open("a.txt") as ffff:

for i in ffff:

print(i)

print(ffff.read(1111))

print(ffff.read())

with open("a") as f: 使用了上下文