Python Abstract: Object-oriented higher order

1. Check for inheritance

If you want to see if a class is a subclass of another class, you can use the built-in Issubclass function

If you want to know the base class of a known class, you can use special attributes directly __bases__

Also, use the Isinstance method to check whether an object is an instance of a class (instance)

If you want to know which class an object belongs to, you can use the __class__ attribute

2. Reflection

The reflection functionality in Python is provided by the following four built-in functions: Hasattr, GetAttr, SetAttr, delattr, and four functions for internal execution of objects: Check for a member, get a member, set a member, delete a member.

classFoo:def __init__(self,name,age): Self.name=name Self.age= AgedefShow (self):return "%s-%s"%(self.name,self.age) obj=foo ('Greg', 18)Print(Obj.name)#Gregb="name"Print(obj.__dict__)#{' name ': ' Greg ', ' age ':Print(obj.__dict__['name'])#GregPrint(obj.__dict__[b])#GregINP=input ('>>>')#What to get inside somethingv=getattr (OBJ,INP)Print(v)
#反射是通过字符串的形式操作对象相关的成员. all things are objects!!! Sho=getattr (obj,'Show')Print(Sho)#<bound method Foo.show of <__main__. Foo object at 0x000001e00c46ca58>>Sh=Sho ()Print(SH)#alex-18Print(Hasattr (obj,'name'))#TruePrint(Hasattr (obj,'name1'))#Falsesetattr (obj,'K1','v1')Print(OBJ.K1) #v1#Obj.namePrint(Delattr (obj,'name')) #NONE#Obj.name

Three ways to get the name variable in the Obj object to point to the value in memory "Gregory"

classFoo (object):def __init__(self): Self.name='Gregory'#do not allow the use of Obj.nameobj =Foo ()Print(Obj.name)Print(obj.__dict__['name'])Print(GetAttr (obj,'name'))

3. Nesting of objects

classF1:def __init__(self): Self.name="Greg"classF2:def __init__(self,a):#A=f1=[name=greg]Self.age=aclassF3:def __init__(SELF,B):#B=f2=[age=name=greg]Self.dd=Bf1=F1 ()#[Name=greg]F2=F2 (F1)#[Age=name=greg]F3=F3 (F2)#[Dd=[age=name=greg]]#print (F3.DD) #<__main__. F2 object at 0x00000232aca612b0>#print (f3.dd.age) #18Print(F3.dd.age.name)#Greg

4. Exception (Exception object)

4.1 Some important built-in anomalies

Attributeerror attempts to access a tree that does not have an object, such as foo.x, but Foo does not have a property xioerror input/output exception; it is basically impossible to open the file Importerror the module or package cannot be introduced is basically a path problem or name error Indentationerror syntax error (subclass); The code is not aligned correctly indexerror the subscript index exceeds the sequence boundary, for example, when X has only three elements, it attempts to access the X[5]keyerror Attempting to access a key that does not exist in the dictionary Keyboardinterrupt CTRL + C is pressed Nameerror use a variable that has not been assigned to the object SyntaxError Python code is illegal, the code cannot compile (personally think this is a syntax error, Wrong) TypeError the incoming object type is not compliant with the requirements Unboundlocalerror attempts to access a local variable that is not yet set, basically because another global variable with the same name causes you to think that you are accessing it valueerror a value that the caller does not expect , even if the type of the value is correct

4.2 Catching exceptions

Try: Li=[11,22] li[999]#can catch errors    #int (' d3de ') #不能捕获错误exceptIndexerror as E:Print('Indexerror', E)exceptValueError as E:Print('ValueError', E)exceptException as E: #在python的异常中, there is a universal exception: Exception, he can catch arbitrary exceptionsPrint('Exception', E)Else:    Print('Else')finally: #finally语句不管try是否发生异常, will be executed. Print('...')

4.3 Active trigger exception

Try :     # proactively triggering exceptions    Raise Exception (' but ... ' )except  Exception as E:    print(e)

The raise statement throws a common exception that does not have any errors.

4.4 Catching exceptions write to log

defdb ():#return True    returnFalsedefindex ():Try: R=input (">>") int (r) Result=db ()if  notResult:RaiseException ('Database processing error')    exceptException as E:str_error=Str (e)Print(Str_error)#Open file, write error logR=open ('Log','a') R.write (str_error) index ()

4.5 Custom Exceptions

classGregerror (Exception):def __init__(self,msg): Self.message=msgdef __str__(self):returnSelf.message#obj=gregerror (' xxx ')#print (obj)Try:    RaiseGregerror ("I was wrong ...")exceptGregerror as E:Print(e)#the __str__ method of the E object, which gets the return value

4.6 Assertions

# Assert Condition Print (123) assert 1==2# assertion print(456)

4.7 Single-Case mode

The purpose of the simple interest mode is to ensure that only a single instance exists in the current memory, avoiding memory waste.

for Python singleton mode, you can no longer use the object directly when you create it: obj = Foo (), and you should call a special method: obj = Foo.get_instance (). examples are as follows:

classFoo:__v=None @classmethoddefget_instance (CLS):ifAl1.__v:#if it has a value            returnAl1.__v        Else: CLS.__v=Foo ()returnAl1.__v#do not use Class () againObj=foo.get_instance ()#objects created by obj=Print(obj) obj2=foo.get_instance ()Print(obj2) obj3=foo.get_instance ()Print(OBJ3)#<__main__. Foo object at 0x000001b5a30e10f0>#<__main__. Foo object at 0x000001b5a30e10f0>#<__main__. Foo object at 0x000001b5a30e10f0>

Python Abstract: Object-oriented higher order