MySQL--07(pymysql)

pip install pymysql

import pymysql

from  functools import  wraps

# 四个参数（连接地址，登录数据库用户，数据连接密码，数据库名字）
db = pymysql.connect('localhost', 'root', 'mysql', 'books')

c = db.cursor()  # 获取游标cursor

## 查询所有表
sql = 'show tables;'
c.execute(sql)  # 执行sql语句
query = c.fetchall()
# fetch 取，获取  all 全部

# print(query)

## 查询books表里的所有记录
sql = 'select * from books'
c.execute(sql)
query = c.fetchall()
# print(query)

# CURD

# sql = '''
# insert into books(book_name,author,publish,prints,publish_date)values
# ('三国演义','罗贯中','中州古籍出版社',100,'2019-04-01');
# '''
# c.execute(sql)
# db.commit()  # 提交
# query=c.fetchall()
# print(query)


sql = 'select * from books'
c.execute(sql)
query = c.fetchall()


# print(query)

# # pymysql 删除数据
# sql ='delete from books where id=4'
# try:
#     c.execute(sql)
#     db.commit()  # 只要涉及到数据变更的，一定要带上 commit
# except:
#     db.rollback()
#

# pymysql 修改数据
# sql='update books set author="四毛" where id=1'
#
# try:
#     c.execute(sql)
#     db.commit()
# except:
#     db.rollback()

# sql='select * from books'
# # [{},{},{}]
# try:
#     c.execute(sql)
#     query =c.fetchall()
#     res =[]
#     for x in query:
#         temp ={}
#         temp['book_name']=x[1]
#         temp['author']=x[2]
#         res.append(temp)
# except:
#     print('查询错误')
#
# print(res)

# c.close()
# db.close()


'''
定义单例装饰器
'''
def singleton(cls):
    _instance ={}  # 定义集合放置cls的实例
    @wraps(cls)
    def getInstance(*args,**kwargs):
        if cls not in _instance:  # 如果没有实例，则生成一个
            _instance[cls]=cls(*args,**kwargs)
        return _instance[cls]   # 返回实例
    return  getInstance


@singleton
class pysql(object):

    def __init__(self):
        print('class instance1')


p1 = pysql()
p2 = pysql()
print(id(p1))
print(id(p2))