Python – Hcitool lescan does not print to a file in real time

Update: I solved my solution using os.system:

sensortag=0
while sensortag != "B4:99:4C:64:33:E0":
    #call the command and write to scan.txt file and then fill the process.
    #loop to find if the MAC address given is available
    os.system("hcitool lescan> scan.txt & pkill --signal SIGINT hcitool")
    scan = open("scan.txt","r")
    readscan = scan.read()
    if "B4:99:4C:64:33:E0" in readscan:
        print "SensorTag found."
        sensortag = "B4:99:4C:64:33:E0"

I have two programs on the Raspberry PI running Raspbian, essentially the same but with two different commands.

What I want to do is write both command outputs to a file so that they can be processed later.

I’m confused as to why the first program doesn’t work while the second does.

The first program has a “sudo timeout 5 HCIotool lescan” command, which does not work.

import os
import subprocess

#r+ because the file is already there, w without the file
myfile = open("scan.txt", "r+")

#Reset Bluetooth interface, hci0
os.system("sudo hciconfig hci0 down")
os.system("sudo hciconfig hci0 up")

#Scan for bluetooth devices
dev = subprocess. Popen(["sudo timeout 5 hcitool lescan"], stdout=subprocess. PIPE, shell=True)
(device, err) = dev.communicate()

#Print bluetooth devices
print device

#Write the hcitool lescan output to a file
myfile.write(device)

#Close the file
myfile.close()

This is my second program and it effectively prints “sudo hciconfig“:

import os
import subprocess

#r+ because the file is already there, w without the file
myfile = open("test.txt", "r+")

#Reset Bluetooth interface, hci0
os.system("sudo hciconfig hci0 down")
os.system("sudo hciconfig hci0 up")

#Make sure device is up
interface = subprocess. Popen(["sudo hciconfig"], stdout=subprocess. PIPE, shell=True)
(int, err) = interface.communicate()

#Print hciconfig to make sure it's up
print int

#Write the hciconfig output to a file
myfile.write(int)

#Close the file
myfile.close()

I solved my solution using os.system and terminated the scan immediately:

sensortag=0
while sensortag != "B4:99:4C:64:33:E0":
    #call the command and write to scan.txt file and then fill the process.
    #loop to find if the MAC address given is available
    os.system("hcitool lescan> scan.txt & pkill --signal SIGINT hcitool")
    scan = open("scan.txt","r")
    readscan = scan.read()
    if "B4:99:4C:64:33:E0" in readscan:
        print "SensorTag found."
        sensortag = "B4:99:4C:64:33:E0"