docs: def _updateNumbers(self, linenumers):
          """
          add/remove line numbers
          """
          b = self.blockCount()
          c = b - linenumers
          if c > 0:
              # remove lines numbers
              for _ in range(c):
                  # remove last line:
                  self.setFocus()
                  storeCursorPos = self.textCursor()
                  self.moveCursor(
                      QtGui.QTextCursor.End,
                      QtGui.QTextCursor.MoveAnchor)
                  self.moveCursor(
                      QtGui.QTextCursor.StartOfLine,
                      QtGui.QTextCursor.MoveAnchor)
                  self.moveCursor(
                      QtGui.QTextCursor.End,
                      QtGui.QTextCursor.KeepAnchor)
                  self.textCursor().removeSelectedText()
                  self.textCursor().deletePreviousChar()
                  self.setTextCursor(storeCursorPos)
          elif c < 0:
              # add line numbers
              for i in range(-c):
                  self.appendPlainText(str(b + i + 1))