Genie is a relatively new language similar to Python but compiles to C based on the Vala compiler. Currently class contents may be set to public (default) or private (with a single underscore before the name). Vala supports a third option, "protected", which is similar to private but accessible to subclasses.
Dig into the valac compiler to change a single underscore to represent "protected" and, following the Python convention, change double underscore before names to represent "private". This will likely only require a few lines of code but will involve a good deal of reading code and learning how code gets tokenized.
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