Python script not reading from Arduino correctly - c

Question

I'm trying to get my Arduino to send data to a python script on my computer and for some reason the python script is reading the data incorrectly. Specifically, it reads the data correctly for about 4-5 receives then it starts to get out of sync. Below is my code:
Arduino:
struct sensorData
{
char beginPad[5];
int data0;
char pad0;
//int data1;
//char pad1;
//int data2;
};
union data
{
unsigned char buffer[sizeof(sensorData)];
sensorData vars;
};
data sendData;
void setup()
{
Serial.begin(9600);
static char temp[5] = {0, 1, 2, 3, 4};
memcpy(sendData.vars.beginPad, temp, 5);
sendData.vars.pad0 = 0;
//sendData.vars.pad1 = 0;
}
void loop()
{
sendData.vars.data0 = (256);
//sendData.vars.data1 = (512);
//sendData.vars.data2 = (1024);
Serial.write(sendData.buffer, sizeof(sensorData));
delay(100);
}
Python:
import serial
class SensorData:
def __init__(self, ser_obj, s_dict, p_start, p_len):
self.ser = ser_obj
self.sensor_buffer = s_dict
self.num_sensors = len(s_dict)
self.pad_start = p_start
self.pad_len = p_len
self.wait_for_beginning(p_start)
def poll(self):
for i in range(self.num_sensors):
tmp = self.ser_read()
tmp+=(self.ser_read()<<8)
print tmp
self.sensor_buffer.values()[i].append(tmp)
self.ser_read()
return self.sensor_buffer
def ser_read(self):
while True:
try:
data = ord(self.ser.read())
break
except:
continue
return data
def wait_for_beginning(self, start):
while True:
while(self.ser_read() != 0): continue
flag = 0
for i in range(1, self.pad_len):
if i == self.ser_read(): continue
else:
flag = 1
break
if flag: continue
else: break
def wait_for_end(self):
while True:
pad = self.ser_read()
if pad == self.pad_len-1:
break
#END OF CLASS
#main.py
def serial_poll( s_dict ):
dev = serial_init()
s = SensorData( dev, s_dict, 0, 5 )
while True:
sensor_buffer = s.poll()
s.wait_for_end()
print sensor_buffer
def serial_init():
ser = serial.Serial()
ser.baudrate = 9600
ser.port = '/dev/ttyACM0'
ser.open()
return ser
if __name__ == "__main__":
global sensor_buffer
sensor_buffer = { 'sensor1': [] }
serial_thread = threading.Thread( target=serial_poll, args=(sensor_buffer, ) )
serial_thread.daemon = True
serial_thread.start()
while True:
time.sleep( .1 )
I'm running the serial functions on a new thread because I have other things going on in this application. I'm basically trying to send some data that I have hard coded from the Arduino to a Linux computer. I have padding in between actual data to delimit it. At first I thought I was getting buffer overflows since each data buffer was more than 14 bytes long. I shortened it and the issue persisted. I then tried to add a delay since it might be sending data too fast. This didn't help either and now I'm out of ideas. If you need me to be more specific just let me know.