Developer Tackles C-Level Dependency Bug Using Structural Subtyping Workaround

An open-source contributor recently used a lighter workweek to focus on writing Python type stub files and addressing a runtime dependency issue in a C source file called unit_list_proxy.c. The problem involved C code aggressively importing a large Python library at object creation, creating a heavy, tangled dependency cycle. Rather than undertaking a full refactor, the developer proposed using structural subtyping — a form of duck typing applied at the C level — which was approved by mentor Clément. This approach checks whether an object has the required behavior rather than verifying its exact type, eliminating the need to import the entire Python library. The solution cleanly breaks the dependency chain without requiring a major rewrite of the underlying code.