see print instance.doc, e.g. cat=LoadFile(kind='excel')
          read how to use cat.load_data, exec: print (cat.doc)

def load_data(self, path, *args, **kwargs):
        """see print instance.doc, e.g. cat=LoadFile(kind='excel')
          read how to use cat.load_data, exec: print (cat.doc)"""
        self.df = self._load(path,*args, **kwargs)
        self.series = self.df.iloc[:,0]
        print ("Success! file length: " +str(self.df.shape[0]))