code: def p0(self):
          
          if self._p0 is None:
              raise ValueError("initial positions not set; run set_p0")
          # convert to dict
          p0 = {param: self._p0[..., k]
                for (k, param) in enumerate(self.sampling_params)}
          return p0
docs: A dictionary of the initial position of the walkers.
  
          This is set by using ``set_p0``. If not set yet, a ``ValueError`` is
          raised when the attribute is accessed.