Python Inheritance relationship and DVD case

1. module. getrefcount--view the number of references, throw an exception if there is no reference, 2. Inheritance: Simplify the code. When a subclass is generated, the parent class inherits the property--①self. Property = Current Property ② Parent class. property = Current Property ③ parent class. The _init_ () method ④super (subclass, Self). _init_ () Method 3. The constructor method (which must have a return value) takes precedence over the initialization method class name. MSO is used to invoke the location of the parent class Def _new_ (cls,*,**): print () return Object._new_ (CLS) 4. Class method: @classmethod require parameters　　　　For example, the constructor method static method: @staticmethod no parameters and classes. The object has no relation 5. Singleton mode: Create only one object construction method inside can be judged # Singleton mode class Sing:__instance=none def __new__ (CLS): If cls.__instance==none:cls.__instance=object.__new__ (CLS) return cls.__instance Else:return cls.__ins　　Tance s=sing () ss=sing () print (ID (s), ID (ss))  6. Object list sort: Override _lt_ () _str_ (), and list output requires loop def _lt_ (Self,other): Return Self.brand.encode ("GBK") <other.brand.encode ("GBK") der _str_ (self): return Self.brand+str (Self.price) 7. Exception handling and write try: statement except exception type as Alias: statement else: No exception is executed finally: statement 8. Use else, general and break using Flag=falsefor I in range (1,11): If i%3= =0:flag=true print (i) Break else:print ("not divisible")  9.pass do nothing at all. Parse the file with the   iterator adornment pattern XML &NBSP;&NBSP;&NB Sp;dvd Management System case: (Divided into simple simulation and optimization) 1. SimpleAnalog (with errors)

Class DVD:
def __init__ (Self,num=none):
Self.num=num
List=[]
Print ("========dvd management system ========\n1. Query all dvd\n2. Add dvd\n3. Lend dvd\n4. Return dvd\n5. Exit")

Class Handler (DVD):
def __init__ (self):
Dvd.__init__ (self)
num = Int (input ("Please enter the number you want to select"))
List=[]
If NUM is 1:
Print (list)
Handler ()
If NUM is 2:
Value=input ("Please enter the name of the DVD")
List.append (value)
Print (list)
Nu=int (Input ("continue adding 0/1"))
If Nu is 0:
Value = input ("Please enter the name of the DVD")
List.append (value)
Print (list)
Handler ()

If NUM is 3:
Value=input ("Please enter the DVD you want to borrow")
List.remove (value)
Print (list)
Handler ()
If NUM is 4:
Value=input ("Please enter the name of the DVD to be returned")
List.append (value)
Print (list)
Handler ()
Else
Print ("Already exited the system! ")
NU=STR (Input ("re-enter System 0/1"))
If Nu is 0:
Handler ()
Else
Pass

S=handler ()

2. Optimization of the case (can continue to optimize, the current requirements are not clear, limited capacity):

Class DVD:
def __init__ (Self,num=none):
Self.num=num
List=[]
Print ("========dvd management system ========\n1. Query all dvd\n2. Add dvd\n3. Lend dvd\n4. Return dvd\n5. Exit")




Class Handler (DVD):
def __init__ (self):
Dvd.__init__ (self)
num = Int (input ("Please enter the number you want to select"))
List=[]
If NUM is 1:
Print (list)
Handler ()
If NUM is 2:
Value=input ("Please enter the name of the DVD")
List.append (value)
Print (list)
Nu=int (Input ("continue adding 0/1"))
If Nu is 0:
Value = input ("Please enter the name of the DVD")
List.append (value)
Print (list)
Handler ()

If NUM is 3:
Value=input ("Please enter the DVD you want to borrow")
List.remove (value)
Print (list)
Handler ()
If NUM is 4:
Value=input ("Please enter the name of the DVD to be returned")
List.append (value)
Print (list)
Handler ()
Else
Print ("Already exited the system! ")
NU=STR (Input ("re-enter System 0/1"))
If Nu is 0:
Handler ()
Else
Pass

S=handler ()

Python Inheritance relationships and DVD cases