review:
#Reflection must know, must be able to read and understand, must know where to use it
#hasattr getattr setattr delattr
Built-in methods must be understandable and usable
The result of __len__len(obj) depends on the result of obj.__len()__ to calculate the length of the object
The result of __hash__ hash(obj) depends on the result of obj.__hash__() to settle the hash value of the object
The result of __eq__ obj1 == obj2 depends on the result of obj.__eq__() to determine equality
__str__ str(obj) print(obj) The result of '%s'%obj depends on __str__, which is used for output and display
__repr__ repr(obj) The result of '%r'%obj depends on __repr__, and can also be used as a spare tire for str
The result of __format__ format() depends on the result of __format__, which is object formatted
__call__ obj() is equivalent to calling __call__, the object that implements __call__ is callable
The __new__ constructor, executed before __init__ is executed, is responsible for creating an object, which has specific applications in the singleton pattern
The __del__ destructor method, which is executed before the object is deleted when the object is deleted, is mainly used to close the system resources opened in the object
class A:
def __getitem__(self, item):
print(item)
a = A()
__getitem__ The new style of object[] adds, deletes, modifies and checks the object
__setitem__
__delitem__
__delattr__ del obj.attr is used to customize the method of deleting an attribute
There is only one object, only one memory space is opened
Create a class object property in the singleton pattern programming static properties in the class, all methods become class methods
Design Patterns---java
The singleton pattern in python is to use __new__
python
Displays all properties starting with a in an object
Second, the module
py files are modules
The reason why python is easy to use, there are many modules
three
1. Built-in modules
It comes with python installation
2. Expansion module
E.g:
itchat
beautiful soap
selenium web automation testing tool
django tornado
3. Custom modules
Built-in modules
serialization module
hashlib module
serialization module
What can be stored in a file must be a string, or a byte
Only bytes can be transmitted over the network
dic = {"layers":(90,23)}
print (str (dic))
print(str(dic).encode(encoding='utf-8'))
##Note that the above Chinese will display the following \xe5........
dic = {"layers":(90,23)}
print (str (dic))
print(str(dic).encode(encoding='utf-8'))
b"{'\xe5\xb1\x82\xe6\x95\xb0': (90, 23)}"
s = b"{'\xe5\xb1\x82\xe6\x95\xb0': (90, 23)}"
res = s.decode(encoding='utf-8')
print(res)
# dic --> string serialization
#string --> dic deserialization
#serialization==create a sequence=="create a string
#instantiate==create an instance
import json
#Serialization
dic = {"john":(190,90)}
ret = json.dumps(dic,ensure_ascii=False)
print(type(dic),dic)
print (type), right)
print('*', str(dic)) #Local method
# deserialize
res = json.loads(ret)
print(type(res),res)
Execution output:
f = open('john','r',encoding='utf-8')
ret = json.load(f)
print (type), right)
execute output
Dump serialization load deserialization is mainly used for a data directly stored in the file to deal with the file directly
Dumps serialization loads deserialization Only operates data in memory Mainly used for network transmission and dealing with multiple data and files
import pickle