code: def to_cartesian(r, theta, theta_units="radians"):
      
      assert theta_units in ['radians', 'degrees'],\
          "kwarg theta_units must specified in radians or degrees"
  
      # Convert to radians
      if theta_units == "degrees":
          theta = to_radians(theta)
  
      theta = to_proper_radians(theta)
      x = r * cos(theta)
      y = r * sin(theta)
  
      return x, y
docs: Converts polar r, theta to cartesian x, y.