docs: def _isinstance(expr, classname):
          """Check whether `expr` is an instance of the class with name
          `classname`
  
          This is like the builtin `isinstance`, but it take the `classname` a
          string, instead of the class directly. Useful for when we don't want to
          import the class for which we want to check (also, remember that
          printer choose rendering method based on the class name, so this is
          totally ok)
          """
          for cls in type(expr).__mro__:
              if cls.__name__ == classname:
                  return True
          return False