Serial communication : Send a list from Python3 to Arduino - python-3.x

Question

I don't manage to deal with my problem even if I have read a lot about it on internet these last few days.
I try to communicate a variable length list from my Python3 program to my Arduino Leonardo.
Actually the length of these lists is variable but there are only three possible length :
first possibility : [0, 0, 1, 176, 1, 0, 0]
second possibility : [0, 1, 11, 255]
third possibility : [0, 2, 0]
(most of the values inside these lists are variables)
My Python3 code :
with Serial(port = port, baudrate=9600, timeout=1, writeTimeout=1) as port_serie :
if port_serie.isOpen() :
for value in Datas_To_Send : #Envoi des données
s = struct.pack('!{0}B'.format(len(Datas_To_Send)), *Datas_To_Send)
port_serie.write(s)
This code sends binary values like this one :
b'\x00\x00\x01\xb0\x01\x00\x00'
(the original list to send was : [0, 0, 1, 176, 1, 0, 0])
The problem is that I absolutely don't know how to find back my original list of values with my Arduino code...
My Arduino code (quite basic) :
void changeSettings() {
if ( Serial.available() > 0 ) {
int byte_read = Serial.read() ;
Serial.println(byte_read, DEC) ;
The output of this code is a pure conversion of each character from the ASCII to the Decimal...
Output (for the binary value I gave as example) :
98
39
92
120
48
48
92
120
48
48
92
120
48
49
92
120
98
48
92
120
48
49
92
120
48
48
92
120
48
48
39
10
Do you have any idea to find the first list back ?
Thank you

Answer 1

It seems you need to transmit either 7, 4 or 3 values, correct?
Are all the values under 256?
So, i would send 1 byte that is either 7, 4 or 3 followed by either 7, 4 or 3 bytes of the list's elements. If any item in your list is greater than 255 and less than 65,536 you'll need to send 2 bytes per element.

Answer 2

Well, I found the solution thanks to #MarkSetchel's and Olmagzar's (Discord user) tips.
Python3 code :
if Datas_To_Send :
long = len(Datas_To_Send)
Datas_To_Send.insert(0, long)
with Serial(port = '/dev/cu.usbmodem14101', baudrate=9600, timeout=1, writeTimeout=1) as port_serie :
if port_serie.isOpen() :
s = struct.pack('!{0}B'.format(len(Datas_To_Send)), *Datas_To_Send)
port_serie.write(s)
port_serie.close()
So I add list length directly at the first position of my list "Datas_To_Send".
Like that I just have to read it first on Arduino's side to know how many items I have to read.
Arduino code :
void changeSettings() {
if (Serial.available() > 0)
{
unsigned char len = Serial.read();
unsigned char Datas[len] ;
for (int i = 0; i < len - 1; i++)
{
unsigned char byte_read = Serial.read();
Datas[i] = byte_read ;
}
}
}