Blender Driver Scripted Expression Tutorials

On a different car, you need to adjust the tire wheel diameter in the Driver 'Scripted Expression', here 0.6 meters. You need to change it for each bone wheel. Another driver is set up for the armature 'steer.track' bone. Check out this post here You can use Math functions directly in driver expressions. To get the current frame you would set up a variable for it in the driver variables panel. Blender 2.79 Manual. Drivers » Workflow & Examples. Here are some examples using the scripted expression Expr to set the Driver Value.

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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 −

• GadFly
• mSQL
• MySQL
• PostgreSQL
• Microsoft SQL Server 2000
• Informix
• Interbase
• Oracle
• Sybase

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 −

• Importing the API module.
• Acquiring a connection with the database.
• Issuing SQL statements and stored procedures.
• Closing the connection

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 −

If it produces the following result, then it means MySQLdb module is not installed −

To install MySQLdb module, use the following command −

Note − Make sure you have root privilege to install above module.

Database Connection

Before connecting to a MySQL database, make sure of the followings −

• You have created a database TESTDB.

• You have created a table EMPLOYEE in TESTDB.

• This table has fields FIRST_NAME, LAST_NAME, AGE, SEX and INCOME.

• User ID 'testuser' and password 'test123' are set to access TESTDB.

• Python module MySQLdb is installed properly on your machine.

• You have gone through MySQL tutorial to understand MySQL Basics.

Example

Following is the example of connecting with MySQL database 'TESTDB'

While running this script, it is producing the following result in my Linux machine.

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 Table

Once a database connection is established, we are ready to create tables or records into the database tables using execute method of the created cursor.

Example

Let us create Database table EMPLOYEE −

INSERT Operation

It is required when you want to create your records into a database table.

Example

The following example, executes SQL INSERT statement to create a record into EMPLOYEE table −

Above example can be written as follows to create SQL queries dynamically −

Example

Following code segment is another form of execution where you can pass parameters directly −

READ Operation

READ 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.

• fetchone() − It fetches the next row of a query result set. A result set is an object that is returned when a cursor object is used to query a table.

• fetchall() − It fetches all the rows in a result set. If some rows have already been extracted from the result set, then it retrievesthe remaining rows from the result set.

• rowcount − This is a read-only attribute and returns the number of rows that were affected by an execute() method.

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Example

The following procedure queries all the records from EMPLOYEE table having salary more than 1000 −

This will produce the following result −

Update Operation

UPDATE 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

DELETE Operation

DELETE 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

Performing Transactions

Transactions are a mechanism that ensures data consistency. Transactions have the following four properties −

• Atomicity − Either a transaction completes or nothing happens at all.

• Indonesia movie 21. Consistency − A transaction must start in a consistent state and leave the system in a consistent state.

• Isolation − Intermediate results of a transaction are not visible outside the current transaction.

• Durability − Once a transaction was committed, the effects are persistent, even after a system failure.

The Python DB API 2.0 provides two methods to either commit or rollback a transaction.

Example

You already know how to implement transactions. Here is again similar example −

COMMIT Operation

Commit 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.

ROLLBACK Operation

If 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.

Disconnecting Database

To disconnect Database connection, use close() method.

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 Errors

There 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.