def sam2fastq(sam, singles = False, force = False):
    L, R = None, None
    for line in sam:
        if line.startswith('@') is True:
            continue
        line = line.strip().split()
        bit = [True if i == '1' else False \
                for i in bin(int(line[1])).split('b')[1][::-1]]
        while len(bit) < 8:
            bit.append(False)
        pair, proper, na, nap, rev, mrev, left, right = bit
        if pair is False:
            if singles is True:
                print_single(line, rev)
            continue
        if rev is True:
            seq = rc(['', line[9]])[1]
            qual = line[10][::-1]
        else:
            seq = line[9]
            qual = line[10]
        if left is True:
            if L is not None and force is False:
                print('sam file is not sorted', file = sys.stderr)
                print('\te.g.: %s' % (line[0]), file = sys.stderr)
                exit()
            if L is not None:
                L = None
                continue
            L = ['@%s' % line[0], seq, '+%s' % line[0], qual]
            if R is not None:
                yield L
                yield R
                L, R = None, None
        if right is True:
            if R is not None and force is False:
                print('sam file is not sorted', file = sys.stderr)
                print('\te.g.: %s' % (line[0]), file = sys.stderr)
                exit()
            if R is not None:
                R = None
                continue
            R = ['@%s' % line[0], seq, '+%s' % line[0], qual]
            if L is not None:
                yield L
                yield R
                L, R = None, None