i need to import data from dynamic column that change every time user select which column to print

1- using this to get all fields and let user choose from them 

model_object_field=fields.Many2one('ir.model.fields', string="choose Field",
                   domain="[('ttype','!=','one2many'),('ttype','!=','many2many')]")

i tried code like this to print out what in the column that user selected 

but it didn't work 

how can i get data from the field and print it 

def out(self,cr):
    sql="select %s from %s"
    ss=cr.excute(sql,[self.model_object_field,self.model_id])
    return ss