Polymorphism (mainly to set the standard, not to inherit the function of the parent class, apply to multiple inheritance)
duck type : strong coupling thought, unify the usage of different things (the idea of unity), users It’s more convenient to use.
Polymorphism: the same thing has multiple forms
代码演示
import abc
class Animal(metaclass=abc.ABCMeta): # 导入adc模块强行统一标准，如果子类的代码不写成talk的函数名调用会直接报错
@abc.abstractmethod
def talk(self):
pass
注意：导入adc模块后的父类只能作为一个标准去定标准，不能再实例化去使用
class Animal:
def talk(self):
pass
class Dog(Animal):
def talk(self):
print("汪汪汪")
class Cat(Animal):
def talk(self):
print("喵喵喵")
class Pig(Animal):
def talk(self):
print("哼哼哼")
obj1 = Dog()
obj2 = Cat()
obj3 = Pig()
obj1.talk()
obj2.talk()
obj3.talk()
def talk(animal):
animal.talk()
talk(obj1)
talk(obj2)
talk(obj3)
len多态原理演示
"aaa".__len__()
[].__len__()
{
}.__len__()
def len(obj):
return obj.__len__()
Built-in method
class Foo:
pass
obj = Foo() # obj是Foo的一个对象，也可以讲Foo是obj的一个实例
print(isinstance(obj, Foo)) # isinstance 用来判断obj是不是Foo的一个实例
print(isinstance([1, 2, 3], list))# isinstance 用来判断[1,2,3]是不是Foo的一个实例
print(issubclass(Foo, object)) # 判断Foo是否是object的子类
__开头并且__结尾的属性会在满足某种条件下自动触发
class People:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self): # str用来控制对象显示打印结果的，str没有参数，返回值必须是str类型
return "%s %s" % (self.name, self.age)
obj = People("nana", 18)
print(obj) # print(obj._str_())
class People:
def __init__(self, name, age):
self.name = name
self.age = age
self.f = open("a.txt", mode="rt", encoding="utf-8")
def __del__(self): # 类的对象被删除后，会自动触发del的运行
self.f.close()
obj = People("nana", 18)
del obj
print("=========end============")
Reflection (all common in classes and objects)
hasattr: determine whether the object has an attribute
getattr: get an attribute in the object (check)
setattr: set an attribute in the object as a new attribute (increase, change. If the attribute is not increased, if there is an overwrite)
delattr: Delete an attribute in the object (delete)
class People:
country = "China"
def __init__(self, name, age):
self.name = name
self.age = age
def tell_info(self):
print(self.name, self.age)
obj = People("nana", 18)
print(hasattr(obj, "country")) # hasattr判断能不能调用到obj.country，会先从对象里面去查看，找不到会从类里面去找
res = getattr(obj, "country") # getattr取值obj.country
print(res)
res = getattr(obj, "tell_info") # getattr可以拿到obj与tell_info的绑定方法
print(res)
method = getattr(obj, "tell_info")
method()
setattr(obj, "xxx", 111) # obj.xxx=111
print(obj.xxx)
delattr(obj, "name") # 删除obj里面self.name
print(obj.name)
Exception handling
What is an
exception ? An exception is a signal that an error occurs.
Once a program goes wrong, an exception will be generated.
If the exception is not handled, the exception will be thrown and the program will stop immediately.
Errors are generally divided into two types:
1. Syntax error
2. Logic error
How to deal with exceptions
Syntax errors -> the program must be corrected before running.
Logic errors -> For logic errors that can be controlled, they should be resolved directly at the code level
. For logic errors that cannot be controlled, try...except...
可控的逻辑错误案例：
age = input("age:").strip()
if age.isdigit():
age = int(age)
if age > 19:
print("too big")
elif age < 19:
print("too small")
else:
print("you got it")
else:
print("输入的必须是数字")
try...except... is a remedy after an exception occurs
# try...except...的完整语法
print（"start..."）
try:
被监测的代码块1
被监测的代码块2
被监测的代码块3
被监测的代码块4
被监测的代码块5
except 异常的类型1 as e：
处理异常的代码
except 异常的类型2 as e:
处理异常的代码
except 异常的类型3 as e：
处理异常的代码
except （异常的类型4，异常的类型5，异常的类型6）as e:
处理异常的代码
except Exception: # Exception可以处理所有的异常，保证程序的正常运行
处理异常的代码
else:
没有发生异常时要执行的代码
finally:
无论异常与否，都会执行该代码，通常用来进行回收资源的操作
print("end..."）
# 注意try可以只跟except，finally联用，但是try不能else联用
try...except...simulating uncontrollable logic case demonstration
案例1：
print("start...")
try:
print(111)
print(222)
l = [11, 22, 33]
l[100]
print(333)
except IndexError as e: # 异常处理对上了就显示异常提示信息，抛出异常后继续执行代码
print(e)
print("end...")
案例2：
print("start...")
try:
print(111)
print(222)
l = [11, 22, 33]
l[100]
print(333)
except KeyError as e: # 异常对不上会直接报错，不会继续执行代码，程序直接崩掉
print(e)
print("end...")
案例3：
print("start...")
try:
print(111)
print(222)
l = [11, 22, 33]
l[0]
dic = {
"k1": 111}
dic["kkk"]
print(333)
except Exception as e: # except Exception可以抛出异常，后继续执行代码
print(e)
else: # 没有发生异常时要执行的代码
print("else的代码")
finally: # 无论异常与否，都会执行该代码，通常用来进行回收资源的操作
print("=====>finally的代码")
print("end...")
Assert raise custom exception
断言代码呈现
l = [111, 222]
# if len(l) != 3:
# raise Exception("必须达到三个值")
assert len(l) == 3 # 判断条件是否成立，如果条件不成立抛出异常，不会再执行后续代码，一般适用于测试代码的时候，如果条件成立，assert就会当作不存在
print("后续代码")
raise
raise IndexError("索引错误") # 主动抛异常,自己指定规则的时候可以用raise制定异常
自定义异常
class Permissio(BaseException):
def __init__(self, msg):
self.msg = msg
raise Permissio("权限错误") # 自己制定异常