Getting wrong values from serial.read() connected to a Raspberry Pi
ser.write(str(x_value));


Writes the string representation of the integer x_value, which is a sequence of ASCII characters.

ByteReceived = (Serial.read());
Serial.print(ByteReceived);


Reads a character (byte) and prints to the value (again as a sequence of characters).

45 51 48 45 53 52 45 49 52 45 52 55 55....


45 is ASCII character value for the character '-', 51 is the character '3', 48 is '0' and so on.

Cheers!