General plan of attack:

• wrap PyConfigParser in another class and pass that around – advantages: configuration will be accessed by properties instead of string keys, minimizing risk of typos; default values will be defined in one place
• consolidate most of the config validations into this class – remove duplication
• add checking for nested types

There will always be need for each phase to have a separate validate method to check more complex properties, though.

My current status is in PR #375: it is using JSON Schema to describe the configuration. It does not require too many changes in the existing codebase, and has the benefit of not having to reimplement the type checking.