def read(self, vlaninheader):
        print("read(): <-", self._full_fn)
        
        with open(self._full_fn) as file:
            # self._lines = file.read().splitlines()
            # self._lines = file.readlines()    # behält '\n'
            self._lines = file.readlines()
        
        vlaninheader = None
        if vlaninheader in self._full_fn:
            print("das VLAN '{vlaninheader}' wurde in '{self._full_fn}' gefunden".format(vlaninheader,  self._full_fn) )
            
        if not self._lines:
            raise OSError("'{}' ist leer!".format(self._full_fn))