Found a nice solution for monitoring selenium tests on headless linux machine

Hey guys, found today from one of my colleagues a good tip about how to debug selenium tests with gui on headless linux. Maybe someone wil find it also helpful. Here's the link

Comparison of python json libs in performance

I work a lot with json in python and never thought before about performance. I was using standard python json lib that goes right from the box, but today found out from one of my colleagues that there is way more faster lib called cjson. I got interested in this and googled a little bit. As a result i got a python script that shows which json lib is faster on Python. Here it is : As a result i got this metrics :

yajl        serialize: 0.308  deserialize: 0.334  total: 0.642
json        serialize: 1.245  deserialize: 1.384  total: 2.629
cjson       serialize: 0.339  deserialize: 0.244  total: 0.583
stdlib json serialize: 1.019  deserialize: 1.396  total: 2.415
ultra json  serialize: 0.170  deserialize: 0.159  total: 0.328
[Finished in 7.0s]

And the winner is ultra json! :) If you want to clone this script for yourself - here's the link  

Rotating a two-dimensional array in Python

I was solving one of the learning tasks on Python and had to rotate two dimensional array clockwise. In Java i would have to loop over array and pass values into newly created array, but in Python i could solve this with one line of code :

 template = zip(*template[::-1])

And an explanation for this line is next : Consider the following two-dimensional list:

original = [[1, 2],
            [3, 4]]

Lets break it down step by step:

original[::-1]   # elements of original are reversed
[[3, 4], [1, 2]]

This list is passed into zip() using argument unpacking, so the zip call ends up being the equivalent of this:

zip([3, 4],
    [1, 2])
#    ^  ^----column 2
#    |-------column 1
# returns [(3, 1), (4, 2)], which is a original rotated clockwise

Hopefully the comments make it clear what zip does, it will group elements from each input iterable based on index, or in other words it groups the columns.

Getting HTTP traffic details from tcpdump

Yestarday i had one issue to verify where i had to make sure that our backend part is sending POST requests with id's to third party server.  Server didn't have GUI , so i couldn't use Wireshark for that ( or could, but just don't know how:) ) and i googled for possible solutions.  So, here're two possible ways that could help you out in such case :
1) Basic one is simply run

 tcpdump -w output.log

and then download this file on your computer, open it in Wireshark and analize with it

2) Or you could try to analyze it in console with this commands :) :

# tcpdump filter for HTTP GET 
sudo tcpdump -s 0 -A 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420'

# tcpdump filter for HTTP POST 
sudo tcpdump -s 0 -A 'tcp dst port 80 and (tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354)'

# monitor HTTP traffic including request and response headers and message body
# cf. https://sites.google.com/site/jimmyxu101/testing/use-tcpdump-to-monitor-http-traffic
tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2 data-blogger-escaped--="" data-blogger-escaped-tcp="" data-blogger-escaped-xf0="">>2)) != 0)'
tcpdump -X -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2 data-blogger-escaped--="" data-blogger-escaped-tcp="" data-blogger-escaped-xf0="">>2)) != 0)'

2) But the easiest and way more better looking option is to use Chaosreader . The script is called chaosreader0.94. See here for more details.  So, you just need to :

1. Run this



 tcpdump host 93.23.40.50 -s 9000 -w outputfile; perl chaosreader0.94 outputfile

2. You can use both IP address of the server or it's direct http url
3. Generate traffic
4. Hit Ctrl+C and look for resuls in html file that chaosreader0.94 will generate for us.

The Hamming distance task solution

I was going through new interesting tasks on http://www.checkio.org/ and faced with bytes task about Hamming distance calculation. Here's some theory about this : 

The Hamming distance between two binary integers is the number of bit positions that differs (http://en.wikipedia.org/wiki/Hamming_distance). For example: 

117 = 0 1 1 1 0 1 0 1 17 = 0 0 0 1 0 0 0 1 H = 0+1+1+0+0+1+0+0 = 3 

And the task was : 

Given two positive integers in decimal form. You should calculate the Hamming distance between these two numbers in binary form.

I don't like tasks with bytes because i don't understand them fully:) So, i started googling and playing around with different solutions. In the end i got my code running and completing the task as it was required : 

And then i got access to other people solutions. Well, it was very surprising and exciting to see this nice, clean and short solution for my problem:) 

def checkio(data):
    a, b = data
    return str(bin(a^b)).count('1')
 
#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio([117, 17]) == 3, "First example"
    assert checkio([1, 2]) == 2, "Second example"
    assert checkio([16, 15]) == 5, "Third example"

Which, we all have to admit, is cool and looks really good. For the one who just start studying python here's some short description of how this cool algorithm works : According to python docs :

Bitwise operator works on bits and perform bit by bit operation. Assume if a = 60; and b = 13; Now in binary format they will be as follows: a = 0011 1100 b = 0000 1101 ----------------- a&b = 0000 1100 a|b = 0011 1101 a^b = 0011 0001 ~a  = 1100 0011

So,

1. bin() - converts ints into bytes
2. a^b - Binary XOR Operator copies the bit if it is set in one operand but not both
3. .count("1") - counts how many 1 in result

Nice and easy:)

P.S. while i was googling about this convertation from int into bytes and back, i found useful python script which i used for my method :

Another cool website for beginners who want to learn Python

Found this today - http://www.checkio.org/ . From my experience i've noticed that learning in a gaming mode goes much better and faster. Besides it's a great motivator to continue studying and getting new perks for successfully finished tasks.  I've already passed all lessons for ruby, python on Codeacademy , finished all tasks on http://codingbat.com and now going to finish this checkio game and win it :) you should try it for youself - python is awesome and fun to learn. 

Needed to make Google think that i'm from US

Since i live in Ukraine right now, sometimes i want to use services that are working only for US citizens. For example Spotify will work for you only if you live in US or in some european countries. I used to user Tunnelbear on my macbook Air and it worked like a charm until some point where it stopped logging in for me:( Since that moment i forgot about this issue and found some alternatives for Spotify. However, yesterday one of my friends asked me about how she can buy Google Nexus 4. I found some articles for her, but before sending it, i decided to check myself how well they work and whether i can get access to Google play where i can order this Nexus 4 device. First solution was to use Firefox + anonymousX plugin, but it didn't worked for me even when i set timezone on my laptop to US and cleared all cookies and cache in Firefox. Second option was to register on one of the web tunnels which can become a VPN provider for you and mask you as a US citizen. I was too lazy for registering on one more web service, that will most likely spam me with e-mails afterwards, and i kept looking. My third and final option was to use Tor browser. I've heard about this project before and it was interesting for me to try it out. Here's what you gonna need  to do: 

• Download it
• Install:)
• Launch at first time, so it will create all needed config files and will connect to Tor network at first time
• Then you're gonna need to open Terminal ( i'm a Mac user) and run next command :

• nano /Applications/TorBrowser_en-US.app/Contents/MacOS/Vidalia.app/Contents/MacOS/../../../../../Library/Vidalia/torrc

• In the end of the file paste this 2 values :

• ExitNodes {US}
  StrictExitNodes 1

• Save it, stop Tor and then start it again
• Now go to https://play.google.com/store and you'll see that devices section is available for you and you can actually select and purchase one of them:) 

You can actually specify any country you need and "simulate" situation when you're accessing your application from another country. I believe that for more simpler tasks you can use both Tor and Firefox + anonymousX plugin, but Tor can be considered as a backup when Firefox fails you. 

Simple HTTP Server that will give serve simple files and can emulate delay before giving response

On one of my projects i had a task where i needed to make a  simple http server that would give one xml file for our service (Trying to emulate and verify sync between two services). But besides that i had also to check that application behaves properly when you get timeout from the server on the other end. So, i've started googling and found really nice and fast solution with python SimpleHTTPServer. I found it here and modified it a little bit for my purposes with delay emulation. Here's the code : 

You can save it as server.py and they simple run it on your server as:

python server.py 8081 0&

It will run this server on 8081 port ( you can change it to any free port you want) . Second value is for delay - 0 if you want server to respond right away, !=0 - set how many seconds you want server to wait before responding.

It's very fast and easy way to check this things, and i'm pretty sure i will use it in the future and maybe will modify and improve it when it will be needed. The beauty of this method is that you don't have to setup any server and launch it. All you need is installed Python ( which is already preinstalled on any Unix machine) and this file.