One 、python Built in basic magic methods
Two 、python Magic method of container type in
3、 ... and 、python Magic method of arithmetic operator in
What is the magic method （ Magic methods / Special methods ）
Magic methods don't need to be called manually
It is triggered under certain circumstances
Magic methods are all in python Defined in advance , When defining methods , Don't use magic naming conventions
The magic method is to start with a double dash , Ending with a double dash
One 、python Built in basic magic methodsinit Method
init Is the method of class instantiation
# for example class Mytest(): def __init__(self): print("---- This is magic __init__")Mytest()call Method
__call__ The role of methods ： The implementation object is callable
1. It didn't come true __call__ When the method is used , Objects are not callable
# class class Demo: pass# Determine whether the object can be called , There is a function that can use ——callableprint(callable(Demo)) ======》 return True, Can be called # demo Class can be called , Cannot be called obj = Demo()obj()Execution results ： Tips ：‘Demo’ object is not callable ----- No, __call__ Method
2. If you want to create an object from a class, do not call , You use __call__ Method
class Demo: def __call__(self, *args,**kwds): print(" This is a __call__ Method executed ")print(callable(Demo))# demo Class can be called （ Cannot be called ）obj = Demo()obj() # Equate to ：obj.__call__() Method obj()obj()
new Method
__new__ The role of methods : Is the method of creating objects
__init__ The role of methods : Is a method used to initialize an object
The object of the class should be able to be called ：
first new Method to create an object , And then through init Method initialization
When will I need it New Method ：
Intervene in the process of class instantiating objects
Be careful :
Generally, do not rewrite new Method , Unless there is a specific need to use new Method to implement
Defined new After method , You need to call the new To create objects And back to
class MyTest(object): # Initialize object def __init__(self): print('-------init------ Method ')# Create objects def __new__(cls, *args, **kwargs): print('------new Method -------') obj = super().__new__(cls) # Calling the new To create objects return obj # And return a new object obj = MyTest()bool(self) Method
Definition should be bool() Behavior at call time , Should return to True or False
class Demo: def __bool__(self): """ Built in functions bool(), Getting the Boolean value of an object will execute this method """ return Trueb = Demo() # Gets the Boolean value of the object , return True or Falseprint(bool(b)) =====》 return Truestr(self) Method
Use print When exporting objects , The content output to the console is generated by __str__ To decide
class Demo: def __str__(self): """ Use print When exporting objects , The content output to the console is generated by __str__ To decide """ return 'zifuc'b = Demo() # str Method s = str('123')print(s) =======》 return 123repr(self) Method
This method also controls the display of objects , Generally, the original information of the object will be displayed
class Demo: def __repr__(self): """ This method also controls the display of objects , Generally, the original information of the object will be displayed """ return 'repr-number'b = Demo() # repr Method s = repr('123')print(s) =======》 return '123'len(self) Method
Get the length of the object
class Demo: def __len__(self): """ This method is to get the length of the object :return: """ return 3 b = Demo() # Get the length of the object print(len(b)) =====》 return 3hash(self) Method
Return object's hash value
class Demo: def __hash__(self): """ This method is to get hash value :return: """ return 999b = Demo() # obtain hash value print(hash(b)) =====》 return 999 Two 、python Magic method of container type in setitem(self, key, value) Method
Defines the behavior of the specified element in the settings container , grammar ：self[key] = value
class Mytest: def __setitem__(self, key, value): return setattr(self, key, value)m = Mytest()print(m.__dict__) No data , Empty dictionary m.name = 'gddg' ==== 》 Set up name attribute , The value is gddgm['age'] = 18 ==== 》 Set up age attribute , The value is 18getitem(self, item) Method
Defines the behavior of getting the specified elements in the container , grammar ： self[key]
class Mytest: def __getitem__(self,item): return getattr(self,item)m = Mytest()print(m['name']) ==== 》 name attribute , The value is gddgdelitem(self, item) Method
Defines the behavior of deleting a specified element in a container , amount to del self[key]
class Mytest: def __delitem__(self,item): delattr(self,item)m = Mytest()del m['name'] ==== 》 Delete name attribute contains(self, item) Method
Define when using member test operators （in or not in） The behavior of time , return True or False
class MyTest: def __contains__(self, item): """ Magic method triggered by member operator """ return Truea = MyTest()b = MyTest()print(a in b) =======》 return TrueIterative protocol ：__iter__ Method
Define the behavior of elements in the iteration container
class IterClass: def __iter__(self): """ __iter__ The return value of a method must be an iterator """ return iter([11, 22, 33, 44]) ===== 》 Returns an iterator li = IterClass()for i in li :print(i )for Traversing objects ： 1、 Of the execution object __iter__ Method ( Return iterator ) 2、 In recycling next Iterate over iterators 3、 ... and 、python Magic method of arithmetic operator in add(a,b) Method and sub(a,b) Method
a = 1b = 2print(a + b) ======》 What is actually carried out is ：a.__add__(a,b)print(a - b) ======》 What is actually carried out is ：a.__sub__(a,b)Whether the string type supports addition and subtraction
a = '123'b = '12'print(a + b) ======》 What is actually carried out is ：a.__add__(a,b)print(a - b) ======》 What is actually carried out is ：a.__sub__(a,b)There is no implementation for string objects __sub__ Method , Therefore, direct use of objects is not supported -
I am redefining __sub__ Method , Implement subtraction of string objects
class MyStr(str): def __sub__(self, other): return self.replace(other, '')a = MyStr('1234')b = MyStr('123')print(a + b) ======= 》 return 1234123print(a - b) ======= 》 return 4This is about python This is the end of the article on magic methods , More about python Magic method content please search the previous articles of the software development network or continue to browse the relevant articles below. I hope you will support the software development network in the future ！
