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import csv

def build_bitmap(row):
    # Determine if secondary bitmap is needed
    used_des = [int(col.split('-')[1]) for col in row if col.startswith("DE-") and row[col].strip()]
    has_secondary = any(de > 64 for de in used_des)

    # 8 bytes for primary bitmap, 8 more for secondary if needed
    bitmap = bytearray(16 if has_secondary else 8)

    for de in used_des:
        if de == 1:
            continue  # Bit 1 is reserved for "secondary bitmap present", set below
        byte_index = (de - 1) // 8
        bit_index = (de - 1) % 8
        bitmap[byte_index] |= 1 << (7 - bit_index)

    # Set bit 1 if secondary bitmap is used
    if has_secondary:
        bitmap[0] |= 1 << 7

    return bytes(bitmap)  # Return as immutable bytes object

# Example reading a CSV
with open("your_file.csv", newline='', encoding='utf-8') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        mti = row["MTI"]
        bitmap = build_bitmap(row)
        print(f"MTI: {mti} | Bitmap: {bitmap.hex().upper()}")