Function too_deeply_nested_error 

pub fn too_deeply_nested_error(
    ast: &Mod,
    source_file: &SourceFile,
    limit: usize,
) -> Result<(), CompileError>

Rejects an AST nested deeper than limit.

The parser grows its own stack, so it returns trees deeper than the passes after it can walk, and each of those recurses without a limit of its own. The symbol table applies the same limit, but compile(..., PyCF_ONLY_AST) returns before reaching it.