The Sidr tree is an important fruit tree in many parts of the world, but it is often affected by various diseases and pests that can impact the quality and quantity of its fruit production. This paper proposes the use of ontology and semantic web technologies with Python programing language to program a diagnosis service for the Sidr tree diseases. Programming a Semantic Web application system and services requires knowledge of many technologies such as Resource Description Framework (RDF), Web Ontology Language (OWL), and SPARQL Query. The underline Web service (Sidr tree disease Web service), has to be programmed in connection to a pre-existing ontology and knowledge base. The service program is made of three main components. These components are the user interface, diagnosis service-related functions, Knowledge base, and query engine. The Python 3.10 code listing in this paper represents only the code related to disease diagnosing service and the Sidr tree ontology (SidrTreeonto). In addition to the listed statements and functions, the complete diagnosing service code contains some other unlisted HTML static and dynamic Web pages. The code is run and tested and found to be simple and easy to use even by unexpert users. Overall, this application will provide a useful tool for Sidr tree farmers and researchers to diagnose and manage diseases affecting their trees.