serial data from avr to python
make sure that the baud rate, number of parity bits, start bits and stop bits  are same in your microcontroller and in your serial terminal program. In every serial terminal applications there are options to set the number of parity bits, start bits e.t.c. So the terminal program expects data in the format which is defined by the you. Install any other serial terminal application and check to see the correct byte is received. If the correct bit is received then it may be the problem with your python program.