print (('\n> Done parsing drug targets: read %s total drugs')%len(drug_targets))这段代码表示什么

Null is a term used in computer programming and database management to refer to the absence of a value or the lack of a defined object or entity. It is often used as a placeholder or default value for variables, fields, or parameters that have not been assigned a specific value. In some programming languages, null is represented as a special keyword or symbol, such as null, nil, or undefined. In databases, null is used to indicate that a particular field or column does not contain any data or has not been assigned a value yet.