code: def _findExpressionStart(self, block):
          
  
          # raise expession on next level, if not found
          expEndBlock, expEndColumn = self._findExpressionEnd(block)
  
          text = expEndBlock.text()[:expEndColumn + 1]
          if text.endswith(')'):
              try:
                  return self.findBracketBackward(expEndBlock, expEndColumn, '(')
              except ValueError:
                  raise UserWarning()
          else:
              return expEndBlock, len(text) - len(self._lastWord(text))
docs: Find start of not finished expression
          Raise UserWarning, if not found