Python 3.8 now uses ast.Constant type and remove types like _ast.Str: ast.Str is a backward compatibility class. See https://bugs.python.org/issue32892 for more information about the Python change.

I had to disable Chameleon benchmark in the performance project: python/pyperformance#47

The AST visitor of Chameleon should support the ast.Constant type added in Python 3.6.