code: def _to_p(self, mode):
          
  
          if self.mode.endswith("A"):
              chans = self.channels[:-1]
              alpha = self.channels[-1]
              self._secondary_mode = self.mode[:-1]
          else:
              chans = self.channels
              alpha = None
              self._secondary_mode = self.mode
  
          palette = []
          selfmask = chans[0].mask
          for chn in chans[1:]:
              selfmask = np.ma.mask_or(selfmask, chn.mask)
          new_chn = np.ma.zeros(self.shape, dtype=int)
          color_nb = 0
  
          for i in range(self.height):
              for j in range(self.width):
                  current_col = tuple([chn[i, j] for chn in chans])
                  try:
                      next(idx
                           for idx in range(len(palette))
                           if palette[idx] == current_col)
                  except StopIteration:
                      idx = color_nb
                      palette.append(current_col)
                      color_nb = color_nb + 1
  
                  new_chn[i, j] = idx
  
          if self.fill_value is not None:
              if self.mode.endswith("A"):
                  current_col = tuple(self.fill_value[:-1])
                  fill_alpha = [self.fill_value[-1]]
              else:
                  current_col = tuple(self.fill_value)
                  fill_alpha = []
              try:
                  next(idx
                       for idx in range(len(palette))
                       if palette[idx] == current_col)
              except StopIteration:
                  idx = color_nb
                  palette.append(current_col)
                  color_nb = color_nb + 1
  
              self.fill_value = [idx] + fill_alpha
  
          new_chn.mask = selfmask
          self.palette = palette
          if alpha is None:
              self.channels = [new_chn]
          else:
              self.channels = [new_chn, alpha]
          self.mode = mode
docs: Convert the image to P or PA mode.