Python Full Stack development * 22 Knowledge Point Summary * 180703

22 Object-oriented---
properties, class methods, static methods, reflection
one. Properties
1. Attribute definition: The method is disguised as a property, although at the level of the code there is no advanced, but make it look more reasonable. (Methods similar to properties)
class Person:
def __init__ (self,name,weight,height):
Self.name=name
Self.weight=weight
Self.height=height
@property
def BMI (self):
return self.weight/self.height**2
P1=person ("Ji Zhe 嚞", 56,1.65)
# Print (P1.bmi ()) # 20.569329660238754 ( not added @property) 
print (P1.BMI) # 20.569329660238754 (plus @property) 
2. Since there are three types of access in the new class, we can define three methods for the same attribute according to the access characteristics of their several properties: Get, modify, delete
class Goods:
def __init__ (self,original_price,discount):
Self.original_price=original_price
Self.discount=discount
@property #获取
def Price (self):
return Self.original_price*self.discount
 @price. Setter  #修改                          
def Price (Self,new_price):
Self.original_price=new_price
 @price. deleter  #删除                         
def Price (self):
del Self.discount

G1=goods (5,0.80) # instantiates an object
print (G1.price ()) # No @property usage 4.0
 Print (g1.price)# automatically executes functions under @property 4.0                        
g1.original_price=10 # Automatic execution @price.setter The following function changes the original price to ten
print (g1.price) # 8
del g1.discount # Automatic execution @price.deleter the following function
print (g1.discount) # ' Goods ' object has no attribute ' discount '


Two. Methods
methods include: Common methods, static methods, and class methods, three methods in memory belong to the class, the difference is that the calling method is different
1. Common method: Called by the object; at least one self parameter; When executing a normal method, the object that invokes the method is automatically assigned the
2. Class method: Called by the class, at least one CLS parameter; When the class method is executed, the class that invokes the method is automatically copied to the CLS; If the object calls the class method, it is automatically
passing the class space to the CLS does not pass the object space to the CLS.
@classmethod
def class_func (CLS): Defines a class method with at least one CLS parameter
class name. Class_func () Call class method
class A:
__name = ' Alex '
def func (self):
print (self, ' in Func ')

@classmethod # class method
def func1 (CLS):
print (CLS, ' in Func1 ')
a1=a ()
A1.func () #<__main__. A object at 0x0000011792f389e8> in func
A.func (A1) #<__main__. A object at 0x0000011792f389e8> in func
 a.func1 () #<class ' __main__. A ' > in func1 automatically gives CLS class space
a1.func1 () #<class ' __main__. A ' > in Func1 object invocation is also an automatic class-transfer space
# What is the use of class methods?
# Direct The class to manipulate the methods in the class, there is no need to create objects at the time of operation, using the class method.
 3. Static method: Called by the class, no default parameter defines a static method in the class, without passing in your class space, object space, can be used as a normal function.
@staticmethod
def static_func ():
class name. Static_func ()
class A:
__name = ' Alex '
def func (self):
print (self, ' in Func ')

@classmethod # class method
def func1 (CLS):
print (CLS, ' in Func1 ')
@staticmethod
def login (username,password):
Print ("Login successful")
A.login ("Alex", "123")
The same point: For all methods, it belongs to the class (non-object), so only one copy is saved in memory. 
Different points: Different method callers, automatically passing arguments when calling a method
three. Reflection
1. The definition of reflection operates on object-related properties through a string; everything in Python is an object (you can use reflection)
2. A total of four reflections (four functions that can be self-reflective)
GetAttr Gets the value corresponding to this property
hasattr Determine if this attribute is in this object
setattr Setting Properties
delattr To delete an object property
3. Usage:
(1). Instantiate an object
class A:
country = ' China '
def __init__ (self, Name, age):
self.name = name
self.age = Age
a1 = A (' Alex ', +)
print (getattr (A1, "Country")) # China
print (getattr (A1, "name")) # Alex
print (hasattr (A1, "Age") # True
SetAttr (A1, "Sex", "male")
print (getattr (A1, "Sex")) # male
delattr (A1, "name")
print (getattr (A1, "name")) # ' A ' object has no attribute ' name '
if Hasattr (A1, "name1"):
print (getattr (A1, ' name1 '))
Else:
print ("No ...") # no

(2). Example of a class
class A:
country = ' China '
job = ' Student '

def __init__ (self, Name, age):
self.name = name
self.age = Age
def func (self):
print (' in Func ')
content=input ("<<<") # input is a string
if Hasattr (a,content): # equivalent if hasattr (A, "string")
Print (GetAttr (a,content))
 Print (GetAttr (A, "func")) # <function A.func at 0x00000145e4f99ae8>
Print (GetAttr (A, "func") (one)) # in Func none (default returns None)
Print (GetAttr (A, "job")) # Student
 Print (GetAttr (A, "Job1", "false")) # False
Print (GetAttr (A, "Job1")) # Error type object ' A ' has no attribute ' job1 '

(3). Examples of other modules
Import Old_boy
object=getattr (Old_boy, "B")
Print (GetAttr (object, "add") # 3,4) # The first way to get a static method in a Old_boy file is add
Print (GetAttr (old_boy. B, ' Add ') (3,4) # The second way
Print (GetAttr (old_boy, ' login ') ("Alex", "123") # Call the login function in the Old_boy file

(4). Example of the current module
Import SYS
def login ():
print (in)

def func3 ():
Print (333)
content=input ("<<<")
 GetAttr (sys.modules[__name__],content) () #
GetAttr (sys.modules[__name__], "func3") () # 333

Python Full Stack development * 22 Knowledge Point Summary * 180703