reading data from arduino with python

im trying to do something which arduino sends bunch of data frequently, and my objective is:

1. every 100 data, make a new file. (lets call it a1, a2, ...)

2. in one generic file, take the average of each of these a files and write it inside of that file as a new line

for experiment i coded my arduino like that:

void setup(){
Serial.begin(9600);
}

void loop(){
Serial.println(random(100,500)); 
delay(20);
}

and here is the python code:

import serial, struct

initialfreq = 0
a = 0
interval = 0

fileName = 'general_list'
general_list = open(fileName, 'wb')

ser = serial.Serial(port = 'COM3', baudrate = 9600)


def mean(numberList):
    return sum(numberList) / len(numberList)



while(1):
  for i in '100' :
      temparray=[]
      fileName = 'interval' + str(initialfreq) + '.data'
      temp_file = open(fileName, 'wb')
      readoff = ser.readline()
      temparray.append(readoff)
      temp_file.write(readoff)


##        temp_file.flush()
print("bitti")
general_list.write(str(interval)+"    "+str(mean(temparray)))
general_list.write(str(mean(temparray)))
initialfreq= initialfreq + 1
a=0`

my problem is,

1. for loop is not working properly, even when i sad 100, its not taking 100 values.

2. arduino sending codes with \n. i cant see them in files but in temparray i see that there is \n 's so its not calculating the average.

thanks a lot guys.