code: def visit_slice(self, node):
          
          lower = node.lower.accept(self) if node.lower else ""
          upper = node.upper.accept(self) if node.upper else ""
          step = node.step.accept(self) if node.step else ""
          if step:
              return "%s:%s:%s" % (lower, upper, step)
          return "%s:%s" % (lower, upper)
docs: return an astroid.Slice node as string