python与数据库连接

Python与数据库的连接是通过各种数据库驱动库来实现的。不同的数据库需要使用不同的库来连接和操作。以下是一些常见的数据库及其对应的Python库：

1. **MySQL**:
- 示例代码：

     import mysql.connector

     conn = mysql.connector.connect(
         host='localhost',
         user='yourusername',
         password='yourpassword',
         database='yourdatabase'
     )

     cursor = conn.cursor()
     cursor.execute("SELECT * FROM yourtable")
     result = cursor.fetchall()
     for row in result:
         print(row)

     cursor.close()
     conn.close()

2. **PostgreSQL**:
- 库：`psycopg2`
- 示例代码：

     import psycopg2

     conn = psycopg2.connect(
         host='localhost',
         database='yourdatabase',
         user='yourusername',
         password='yourpassword'
     )

     cursor = conn.cursor()
     cursor.execute("SELECT * FROM yourtable")
     result = cursor.fetchall()
     for row in result:
         print(row)

     cursor.close()
     conn.close()

3. **SQLite**:
- 库：`sqlite3` (内置库)
- 示例代码：

     import sqlite3

     conn = sqlite3.connect('yourdatabase.db')
     cursor = conn.cursor()
     cursor.execute("SELECT * FROM yourtable")
     result = cursor.fetchall()
     for row in result:
         print(row)

     cursor.close()
     conn.close()

4. **MongoDB**:
- 库：`pymongo`
- 示例代码：

     from pymongo import MongoClient

     client = MongoClient('mongodb://localhost:27017/')
     db = client['yourdatabase']
     collection = db['yourcollection']

     results = collection.find()
     for document in results:
         print(document)

     client.close()

这些库提供了丰富的功能来连接和操作数据库，包括执行SQL语句、处理结果集、管理事务等。