Design of a blocks-based environment for introductory programming in Python

This paper details the design of a visual blocks-based tool for editing Python programs. Its purpose is to close the gap between programming using a simplified blocks-based language and textual programming in a mainstream language. As well as helping to guarantee the syntactic validity of programs, the tool aims to reduce the occurrence of run-time errors, a source of learner frustration with dynamic languages, by ensuring that constructed programs will remain well-typed during execution. The design promotes understanding of how data types are used in the language by representing them using colors: each expression block is colored according to its type, and each unfilled hole contains colors which indicate valid argument types. Connected blocks preserve conventional use of whitespace, demonstrating good practice for novice programmers.