Python学习笔记 - PostgreSQL的使用

Posted 2020-10-24 昨日微风

一、安装PostgreSQL模块

pip install psycopg2

有时候会失败，多安装2次就好了(我是第二次成功了)。

二、数据库连接接口

由于Python统一了数据库连接的接口，所以psycopg2和 MySQLdb 在使用方式上是类似的：

 

pymysql.Connect()参数说明
host(str):      MySQL服务器地址
port(int):      MySQL服务器端口号
user(str):      用户名
password(str):  密码
database(str):  数据库名称

connection对象支持的方法
cursor()        使用该连接创建并返回游标
commit()        提交当前事务
rollback()      回滚当前事务
close()         关闭连接

cursor对象支持的方法
execute(op)     执行一个数据库的查询命令
fetchone()      取得结果集的下一行
fetchmany(size) 获取结果集的下几行
fetchall()      获取结果集中的所有行
rowcount()      返回数据条数或影响行数
close()         关闭游标对象

 

 

三、范例

MySql脚本

 

-- ----------------------------
-- Table structure for account
-- ----------------------------
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account`  (
  `acctid` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `name` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `money` decimal(50, 0) NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of account
-- ----------------------------
INSERT INTO `account` VALUES (\'1\', \'张三\', 50);
INSERT INTO `account` VALUES (\'2\', \'李四\', 150);

 

 

Python程序

 

#   coding:utf8
import sys
import psycopg2 #PostgreSQL

class TransferMoney(object):
    def __init__(self, conn):
        self.conn = conn

    def check_acct_available(self, acctid):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=\'%s\'" % acctid
            print("check_acct_available:" + sql)
            cursor.execute(sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("帐号%s不存在" % acctid)
        finally:
            cursor.close()

    def has_enough_money(self, acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=\'%s\' and money>%s" % (
                acctid, money)
            print("has_enough_money:" + sql)
            cursor.execute(sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("帐号%s没有足够的金额" % acctid)
        finally:
            cursor.close()

    def reduce_money(self, acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money-%s where acctid=\'%s\' " % (
                money, acctid)
            print("reduce_money:" + sql)
            cursor.execute(sql)
            if cursor.rowcount != 1:
                raise Exception("帐号%s减款失败" % acctid)
        finally:
            cursor.close()

    def add_money(self, acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money+%s where acctid=\'%s\' " % (
                money, acctid)
            print("add_money:" + sql)
            cursor.execute(sql)
            if cursor.rowcount != 1:
                raise Exception("帐号%s加款失败" % acctid)
        finally:
            cursor.close()

    def transfer(self, source_acctid, target_acctid, money):
        try:
            self.check_acct_available(source_acctid)
            self.check_acct_available(target_acctid)
            self.has_enough_money(source_acctid, money)
            self.reduce_money(source_acctid, money)
            self.add_money(target_acctid, money)
            self.conn.commit()
        except Exception as e:
            self.conn.rollback()
            print("transfer出现异常：" + str(e))
            raise e


def main():
    source_acctid = sys.argv[1]
    print("转出帐号=" + source_acctid)
    target_acctid = sys.argv[2]
    print("转入帐号=" + target_acctid)
    money = sys.argv[3]
    print("金额=" + money)

    # 连接数据库 MySql
    #conn = pymysql.Connect(
    #    host=\'localhost\',
    #    port=3306,
    #    user=\'root\',
    #    passwd=\'root\',
    #    db=\'OtkDb\',
    #    charset=\'utf8\')

　　　 # 连接数据库PostgreSQL

　　　　conn = psycopg2.connect(

　　　　　　host=\'localhost\',

　　　　　　port=5432,

　　　　　　user=\'postgres\',

　　　　　　password=\'postgres\',

　　　　　　database=\'OtkDb\')

    tr_money = TransferMoney(conn)

    try:
        tr_money.transfer(source_acctid, target_acctid, money)
    except Exception as e:
        print("main出现异常：" + str(e))
    finally:
        conn.close()


if __name__ == \'__main__\':
    main()

 

 四、运行效果

 

PS H:\\web\\Python> & python h:\\web\\Python\\01.MySql\\db.py 1 2 50
转出帐号=1
转入帐号=2
金额=50
check_acct_available:select * from account where acctid=\'1\'
check_acct_available:select * from account where acctid=\'2\'
has_enough_money:select * from account where acctid=\'1\' and money>50
reduce_money:update account set money=money-50 where acctid=\'1\'
add_money:update account set money=money+50 where acctid=\'2\'


PS H:\\web\\Python> & python h:\\web\\Python\\01.MySql\\db.py 1 2 50
转出帐号=1
转入帐号=2
金额=50
check_acct_available:select * from account where acctid=\'1\'
check_acct_available:select * from account where acctid=\'2\'
has_enough_money:select * from account where acctid=\'1\' and money>50
transfer出现异常：帐号1没有足够的金额
main出现异常：帐号1没有足够的金额

 

 

参考：

https://www.cnblogs.com/Erick-L/p/7106816.html