def invert_sym(sym_op):
    """
    Invert the sign of the given symmetry operation
    Usage:
      new_op = invert_sym(sym_op)
      sym_op = str symmetry operation e.g. 'x,y,z'
      new_op = inverted symmetry
    E.G.
      new_op = invert_sym('x,y,z')
      >> new_op = '-x,-y,-z'
    """
    sym_op = sym_op.lower()
    new_op = sym_op.replace('x', '-x').replace('y', '-y').replace('z', '-z').replace('--', '+').replace('+-', '-')
    return new_op