def ser_uint256(u):
    rs = b''
    for _ in range(8):
        rs += struct.pack('<I', (u & 4294967295))
        u >>= 32
    return rs
def ser_uint256(u):
    rs = b
    for _ in range(8):
        rs += struct.pack('<I', (u & 4294967295))
        u >>= 32
    return rs