code: def _str_base(self):
      return ",".join(
          [
              str(self.v),
              str(self.v_min),
              str(self.v_max),
              str(self.v_steps),
          ]
      )
  
imports: from sympy.core.singleton import S
  from sympy.core.symbol import Symbol
  from sympy.core.sympify import sympify
  from sympy.core.numbers import Integer
label_desc: Use image node_id 14 for calling the PlotInterval obj's underlying member method code with example usage: obj._str_base() and returns: str