python summary

1. The difference between mysql and MongoDB:

Both MySQL and MongoDB are common open source databases , but MySQL is a traditional relational database , and MongoDB is a non- relational database , also called a document database, which is a NoSQL (not only sql non-relational database) database. They each have their own advantages, the key is to see where they are used. Therefore, those SQL (full name Structured Query Language) statements that we are familiar with are not applicable to MongoDB, because SQL statements are the standard language of relational databases.

 

    Take our company's project as an example. In the early projects, we were all using relational databases, including SQLServer, Oracle, and DB2. Later, we all switched to Mysql. The reason is very simple: Mysql has the advantage of open source under the condition of good performance. Mysql's transactionality and high performance are our main considerations. Later, because the project will use the user system, there will be a large amount of user data for interaction - mass storage, Mysql's read and write speed will be a little bit bottleneck, so we think of Nosql, which has developed very strongly recently. With the development of Nosql's early memcache, many non-relational databases appeared, such as redis and mongodb. After a period of testing, the read and write speeds of redis and mongodb do have obvious advantages over Mysql. The write speed of mongodb is about 2.5W/time per second.

 

    mongodb is stored in BSON structure (binary), which has obvious advantages for mass data storage. The following is a comparison of the operation commands of Mongodb and Mysql.

effect	MySQL	MongoDB
server daemon	mysqld	mongod
Client Tools	mysql	mongo
Logical Backup Tool	mysqldump	mongodump
Logical restore tool	mysql	mongorestore
Data export tool	mysqldump	mongoexport
Data import tool	source	mongoimport
Create a new user and authorize	grant all on *.* to username@'localhost'  identified by 'passwd';	db.addUser("user","psw") db.auth("user","psw")
show library list	show databases;	show dbs
go into the library	use dbname;	use dbname
Show table list	show tables;	show collections
Query master-slave status	show slave status;	rs.status
Create library	create database name;	No need to create it separately, just use it directly
create table	create table tname(id int);	No need to create separately, insert data directly
delete table	drop table tname;	db.tname.drop()
delete library	drop database dbname;	First go into the library, db.dropDatabase()
insert record	insert into tname(id) value(2);	db.tname.insert({id:2})
Delete Record	delete from tname where id=2;	db.tname.remove({id:2})
Modify/ update records	update tname set id=3 where id=2;	db.tname.update({id:2}, {$set:{id:3}},false,true)
query all records	select * from tname;	db.tname.find()
query all columns	select id from tname;	db.tname.find({},{id:1})
Conditional query	select * from tname where id=2;	db.tname.find({id:2})
Conditional query	select * from tname where id < 2;	db.tname.find({id:{$lt:2}})
Conditional query	select * from tname where id >=2;	db.tname.find({id:{$gte:2}})
Conditional query	select * from tname where id=2 and name='steve';	db.tname.find({id:2, name:'steve'})
Conditional query	select * from tname where id=2 or name='steve';	db.tname.find($or:[{id:2}, {name:'steve'}])
Conditional query	select * from tname limit 1;	db.tname.findOne()
fuzzy query	select * from tname where name like "%ste%";	db.tname.find({name:/ste/})
fuzzy query	select * from tname where name like "ste%";	db.tname.find({name:/^ste/})
Get the number of table records	select count(id) from tname;	db.tname.count()
Get conditional record count	select count(id) from tname where id=2;	db.tname.find({id:2}).count()
Remove duplicate values ​​when querying	select distinct(last_name) from tname;	db.tname.distinct('last_name')
Positive sort query	select *from tname order by id;	db.tname.find().sort({id:1})
reverse sort query	select *from tname order by id desc;	db.tname.find().sort({id:-1})
take storage path	explain select * from tname where id=3;	db.tname.find({id=3}).explain()

Special note: mongodb insert multiple fields syntax

> db.user.insert({id:1,name:'steve',sex:'male'})  正确

> db.user.insert({id:2},{name:'bear'},{sex:'female'})  错误

 2. The respective advantages of Django, Tornado, and Flask Framework

Django: Django has no sockets. The purpose of Django is to be easy and fast to develop, and follow the MVC design. Multiple components can easily serve the entire framework in the form of "plug-ins". Django has many powerful third-party plug-ins. Django is very extensible.

Tornado: It is a non-blocking server, and the speed is quite fast, thanks to its non-blocking method and the use of epoll, Future object, disadvantages: no session, needs to be customized

 Flask：是一个微型的web框架，配合SQLALchemy来使用，jinja2模板， werkzeug接口       

3、单例：

class SingleSimple():
    instance=None#类属性
    def __new__(cls, *args, **kwargs):#限制生成对象,c创建对象
        if cls.instance==None:
            cls.instance=object.__new__(cls)#生成新对象
        return cls.instance
    def __init__(self,name):#必须调用，必须加参；
        print('正在初始化方法...')
        self.name=name
s=SingleSimple('abc')
ss=SingleSimple('dfjf')
print(s.name)
print(ss.name)

二、电脑配置

1、操作系统

Windows操作系统：win7、win8、XP

Unix操作系统：FreeBSD、Sun Solaris   一般用于银行、电信、移动、核心业务等高端领域，是收费的，闭源的，很贵

Linux：Ret Hat(红帽）、Ubuntu(游戏3D)、Fedora（社区版）  服务器基本都是Linux系统，维护。

Linux构成：Linux内核和外围程序（shell、gnome。。）

三、