Can we connect python to database?
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The following example shows how to connect to the MySQL server:
Section 7.1, “Connector/Python Connection Arguments” describes the permitted connection arguments. It is also possible to create connection objects using the connection.MySQLConnection() class:
Both forms (either using the To handle connection errors, use the
Defining connection arguments in a dictionary and using the
Using the Connector/Python Python or C Extension Connector/Python offers two implementations: a pure Python interface and a C
extension that uses the MySQL C client library (see Chapter 8, The Connector/Python C Extension). This can be configured at runtime using the Note The The following example shows how to set
It is also possible to use the C Extension directly by importing the The Python standard for database interfaces is the Python DB-API. Most Python database interfaces adhere to this standard. You can choose the right database for your application. Python Database API supports a wide range of database servers such as −
Here is the list of available Python database interfaces: Python Database Interfaces and APIs. You must download a separate DB API module for each database you need to access. For example, if you need to access an Oracle database as well as a MySQL database, you must download both the Oracle and the MySQL database modules. The DB API provides a minimal standard for working with databases using Python structures and syntax wherever possible. This API includes the following −
We would learn all the concepts using MySQL, so let us talk about MySQLdb module. What is MySQLdb?MySQLdb is an interface for connecting to a MySQL database server from Python. It implements the Python Database API v2.0 and is built on top of the MySQL C API. How do I Install MySQLdb?Before proceeding, you make sure you have MySQLdb installed on your machine. Just type the following in your Python script and execute it − #!/usr/bin/python import MySQLdb If it produces the following result, then it means MySQLdb module is not installed − Traceback (most recent call last): File "test.py", line 3, in To install MySQLdb module, use the following command − For Ubuntu, use the following command - $ sudo apt-get install python-pip python-dev libmysqlclient-dev For Fedora, use the following command - $ sudo dnf install python python-devel mysql-devel redhat-rpm-config gcc For Python command prompt, use the following command - pip install MySQL-python Note − Make sure you have root privilege to install above module. Database ConnectionBefore connecting to a MySQL database, make sure of the followings −
ExampleFollowing is the example of connecting with MySQL database "TESTDB" #!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # execute SQL query using execute() method. cursor.execute("SELECT VERSION()") # Fetch a single row using fetchone() method. data = cursor.fetchone() print "Database version : %s " % data # disconnect from server db.close() While running this script, it is producing the following result in my Linux machine. Database version : 5.0.45 If a connection is established with the datasource, then a Connection Object is returned and saved into db for further use, otherwise db is set to None. Next, db object is used to create a cursor object, which in turn is used to execute SQL queries. Finally, before coming out, it ensures that database connection is closed and resources are released. Creating Database TableOnce a database connection is established, we are ready to create tables or records into the database tables using execute method of the created cursor. ExampleLet us create Database table EMPLOYEE − #!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # Drop table if it already exist using execute() method. cursor.execute("DROP TABLE IF EXISTS EMPLOYEE") # Create table as per requirement sql = """CREATE TABLE EMPLOYEE ( FIRST_NAME CHAR(20) NOT NULL, LAST_NAME CHAR(20), AGE INT, SEX CHAR(1), INCOME FLOAT )""" cursor.execute(sql) # disconnect from server db.close() INSERT OperationIt is required when you want to create your records into a database table. ExampleThe following example, executes SQL INSERT statement to create a record into EMPLOYEE table − #!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # Prepare SQL query to INSERT a record into the database. sql = """INSERT INTO EMPLOYEE(FIRST_NAME, LAST_NAME, AGE, SEX, INCOME) VALUES ('Mac', 'Mohan', 20, 'M', 2000)""" try: # Execute the SQL command cursor.execute(sql) # Commit your changes in the database db.commit() except: # Rollback in case there is any error db.rollback() # disconnect from server db.close() Above example can be written as follows to create SQL queries dynamically − #!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # Prepare SQL query to INSERT a record into the database. sql = "INSERT INTO EMPLOYEE(FIRST_NAME, \ LAST_NAME, AGE, SEX, INCOME) \ VALUES ('%s', '%s', '%d', '%c', '%d' )" % \ ('Mac', 'Mohan', 20, 'M', 2000) try: # Execute the SQL command cursor.execute(sql) # Commit your changes in the database db.commit() except: # Rollback in case there is any error db.rollback() # disconnect from server db.close() ExampleFollowing code segment is another form of execution where you can pass parameters directly − .................................. user_id = "test123" password = "password" con.execute('insert into Login values("%s", "%s")' % \ (user_id, password)) .................................. READ OperationREAD Operation on any database means to fetch some useful information from the database. Once our database connection is established, you are ready to make a query into this database. You can use either fetchone() method to fetch single record or fetchall() method to fetech multiple values from a database table.
ExampleThe following procedure queries all the records from EMPLOYEE table having salary more than 1000 − #!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() sql = "SELECT * FROM EMPLOYEE \ WHERE INCOME > '%d'" % (1000) try: # Execute the SQL command cursor.execute(sql) # Fetch all the rows in a list of lists. results = cursor.fetchall() for row in results: fname = row[0] lname = row[1] age = row[2] sex = row[3] income = row[4] # Now print fetched result print "fname=%s,lname=%s,age=%d,sex=%s,income=%d" % \ (fname, lname, age, sex, income ) except: print "Error: unable to fecth data" # disconnect from server db.close() This will produce the following result − fname=Mac, lname=Mohan, age=20, sex=M, income=2000 Update OperationUPDATE Operation on any database means to update one or more records, which are already available in the database. The following procedure updates all the records having SEX as 'M'. Here, we increase AGE of all the males by one year. Example#!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # Prepare SQL query to UPDATE required records sql = "UPDATE EMPLOYEE SET AGE = AGE + 1 WHERE SEX = '%c'" % ('M') try: # Execute the SQL command cursor.execute(sql) # Commit your changes in the database db.commit() except: # Rollback in case there is any error db.rollback() # disconnect from server db.close() DELETE OperationDELETE operation is required when you want to delete some records from your database. Following is the procedure to delete all the records from EMPLOYEE where AGE is more than 20 − Example#!/usr/bin/python import MySQLdb # Open database connection db = MySQLdb.connect("localhost","testuser","test123","TESTDB" ) # prepare a cursor object using cursor() method cursor = db.cursor() # Prepare SQL query to DELETE required records sql = "DELETE FROM EMPLOYEE WHERE AGE > '%d'" % (20) try: # Execute the SQL command cursor.execute(sql) # Commit your changes in the database db.commit() except: # Rollback in case there is any error db.rollback() # disconnect from server db.close() Performing TransactionsTransactions are a mechanism that ensures data consistency. Transactions have the following four properties −
The Python DB API 2.0 provides two methods to either commit or rollback a transaction. ExampleYou already know how to implement transactions. Here is again similar example − # Prepare SQL query to DELETE required records sql = "DELETE FROM EMPLOYEE WHERE AGE > '%d'" % (20) try: # Execute the SQL command cursor.execute(sql) # Commit your changes in the database db.commit() except: # Rollback in case there is any error db.rollback() COMMIT OperationCommit is the operation, which gives a green signal to database to finalize the changes, and after this operation, no change can be reverted back. Here is a simple example to call commit method. db.commit() ROLLBACK OperationIf you are not satisfied with one or more of the changes and you want to revert back those changes completely, then use rollback() method. Here is a simple example to call rollback() method. db.rollback() Disconnecting DatabaseTo disconnect Database connection, use close() method. db.close() If the connection to a database is closed by the user with the close() method, any outstanding transactions are rolled back by the DB. However, instead of depending on any of DB lower level implementation details, your application would be better off calling commit or rollback explicitly. Handling ErrorsThere are many sources of errors. A few examples are a syntax error in an executed SQL statement, a connection failure, or calling the fetch method for an already canceled or finished statement handle. The DB API defines a number of errors that must exist in each database module. The following table lists these exceptions.
Your Python scripts should handle these errors, but before using any of the above exceptions, make sure your MySQLdb has support for that exception. You can get more information about them by reading the DB API 2.0 specification. Can we connect MySQL database with Python?The connect() constructor creates a connection to the MySQL server and returns a MySQLConnection object. Section 7.1, “Connector/Python Connection Arguments” describes the permitted connection arguments.
Can you connect SQL to Python?You can connect to a SQL Database using Python on Windows, Linux, or macOS.
How does Python 3 connect to database?How to connect MySQL database in Python. Install MySQL connector module. Use the pip command to install MySQL connector Python. ... . Import MySQL connector module. ... . Use the connect() method. ... . Use the cursor() method. ... . Use the execute() method. ... . Extract result using fetchall() ... . Close cursor and connection objects.. |