Read DNA from a 2bit file where each base is encoded in 2bit 
        (4 bases per byte).
        
        Parameters
        ----------
        l : tuple
            Location tuple
        
        Returns
        -------
        list
            Array of base chars

def _read_dna(self, l, lowercase=False):
        """
        Read DNA from a 2bit file where each base is encoded in 2bit 
        (4 bases per byte).
        
        Parameters
        ----------
        l : tuple
            Location tuple
        
        Returns
        -------
        list
            Array of base chars
        """
        
        file = os.path.join(self.dir, l.chr + ".dna.2bit")
        
        print(file)
        
        if not os.path.exists(file):
            return bytearray([])
       
        f = open(file, 'rb')
        f.seek((l.start - 1) // 4)
        # read bytes into buffer
        data = f.read(l.length // 4 + 2)
        f.close()
        
        return DNA2Bit._read2bit(data, l)