Tracing dynamic features in python programs.

Recent years have seen a number of proposals for adding (retrofitting) static typing to dynamic programming languages, a natural consequence of their growing popularity for non-toy applications across a multitude of domains. These proposals often make assumptions about how programmers write code, and in many cases restrict the way the languages can be used. In the context of Python, this paper describes early results from trace-based collection of run-time data about the use of built-in language features which are inherently hard to type, such as dynamic code generation. The end goal of this work is to facilitate static validation tooling for Python, in particular retrofitting of type systems.