115Ways Not to Say Hello, World!: Syntax Errors Observed in a Large-Scale Online CS0 Python Course

Online programming courses can provide detailed automatic feedback for code that fails to meet various test conditions, but novice students often struggle with syntax errors and are unable to write valid testable code. Even for very simple exercises, the range of incorrect code can be surprising to educators with mastery of a programming language. This research paper presents an analysis of the error messages from code run by students in an introductory Python 3 programming course, participated in by 8680 primary and high-school students from 680 institutions. The invalid programs demonstrate a wide diversity of mistakes: even for a one-line "Hello World!" exercise there were 115 unique invalid programs. The most common errors are identified and compared to the topics introduced in the course. The most generic errors in selected exercises are investigated in greater detail to understand the underlying causes. While the majority of students attempting an exercise reach a successful outcome, many students encounter at least one error in their code. Of these, many such errors indicate basic mistakes, such as unquoted string literals, even in exercises late in the course for which some proficiency of earlier concepts is assumed. These observations suggest there is significant scope to provide greater reinforcement of students' understanding of earlier concepts.