Design Pattern: Singleton

“Beauty!”, when I see some really amazing code that is my first reaction, but what makes a piece of code beautiful? Is it neatly named variables? Is it the uniform indentation?

Well the answer is yes but there is something a little more than these factors and that is an elegant  solution to the problem. When I say elegant solution what is that I am talking about ? What makes a solution elegant? It is the way you approach a problem.

Design Patterns in the programming world adds to the beauty of the solution, it sometimes feels that it is the missing piece of the puzzle. And the solution so magically fits to solve the problem. The various patterns that I came across are Singleton, Mixin, Pub-Sub etc. The way I approached it and studied them is a little different, design patterns are actually tailored way to react to a given situation.

Let me elaborate on that now suppose there is an emergency and somebody got hurt, what is the first thought that comes to your mind ? It is to handle it using First Aid, this is actually a catered thought which has been imbibed in us from ages and people have design First Aid boxes in such a way that it has all the first come fixes for all the emergencies.

For me I see Design Pattern in the same manner it has gone through the test of time and proved to be the best way to solve a specific type of problem.  It is like a ready made template but you should be aware enough to know the problem and to know the pattern that solves that problem. 

I have read about a lot of design patterns but to be very frank I have seldom seen one being applied in the code-base that I have came across, this could be because I have not appreciated it much and also because I was not able to observe the pattern. It was very recently when I was working with Gautham Sir I began to appreciate the beauty of it. We were writing a utility in jnaapti using EcmaScript 6. He made me feel to appreciate the beauty of it and taught me how to implement it as well.

Let us break it down more and see the type of problems in which Singleton design pattern can be used.

What is Singleton design pattern?

A Singleton¬†design pattern puts a restriction of returning the same object irrespective of how many times the class¬†is being instantiated. This makes sure that whatever is the state¬†of object that state is preserved. Don’t be overwhelmed if you are not able to understand it now it will make more sense once you see the code.

The benefit you get is having a kind of a global store where you can put in data and retrieve it when you desire to.

Lets us make it more clear imagine there is a class Library now through out the life cycle of the software what we want is there should be only one Library object and when ever I get this object I should be able to add and delete books from the library hence modifying the library now when I do this the library object anywhere being use should get this information.

Lets chalk out some code and try to understand it, I have 3 files Library.js, Customer.js and LibraryPlayGround.js.  The content of those file are very straight forward.

es6-12
Library.js

Now we need customers or readers for simplifying things i have only included on one method that is return books.

es6-2
Customer.js

Once all this is done we need a playground where we can see things happening and experiment with it.

es6-3
LibraryPlaygroud.js

Now if you see the code farhaan object has tried to access the same Library object that is being exported. No matter what it well return the same instance which has been instantiated in the beginning of the lifecycle of the software. This is how I tried implementing Singleton .

I have used ECMAScript here to demonstrate that concept and to implement it, I am a learner so there could have been certain things I wouldn’t have made clear, you can leave a comment regarding the same, if you have something to add I would love to know.

Till then Happy Hacking

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The A/V guy’s take on PyCon Pune

The A/V guy’s take on PyCon Pune

“This is crazy!”, that was my reaction at some point in PyCon Pune. This is one of my first conference where I participated in a lot of things starting from the website to audio/video and of course being the speaker. I saw a lot of aspects of how a conference works and where what can go wrong. I met some amazing people, people who impacted my life , people who I will never forget. I received so much of love and affection that I can never express in words. ¬†So before writing anything else I want to thank each and everyone of you , “Thank you!”.

My experience or association started the time when the PyCon Pune was being conceived Sayan asked me if I could volunteer for Droidcon so that I can learn how to handle A/V for PP, ¬†and our friends at HasGeek were generous enough to let me do that. The experience at Droidcon was crazy, I met a lot of people and made crazy lot of friends. Basically me and Haseeb were volunteering to learn the A/V stuff and Karthik was patient enough to walk us through the whole complex set up, to be very honest I didn’t get the whole picture till now but I some how able to manage. I learned a thing or two about ¬†manning¬†the camera and how much work actually goes to record a conference.

Since I was anyhow going to the conference I thought why not to apply for a talk but somehow I knew I wasn’t going to make it reason being the talks got rejected in a lot of other conferences ūüėõ . But anyhow being my stubborn self I don’t give up on rejection I gathered all the courage and got Vivek involved and we decided to apply for the talk and to my surprise it got in. This was our first conference talk and it was on one of the projects that we really really love, Pagure.

Since these things happened over a large span of time, by the time conference dates came I have nearly got out of touch with the A/V setup I only have vague idea about what is happening. So Sayan who is a one man army stepped in and he assured me that he will help me with getting the setup ready and we turned again to our friends at HasGeek and they were really humble to help us out this time and also help us with the instruments. We literally had a suitcase full of wires in case things go wrong. We spend around 3 days to up skill ourselves to handle the setup but this time the setup was very simple.

After all this happened and Sayan and Chandan took all the instruments to Pune. I arrived at Pune somewhere around two days before the conference the bus that I took from Bangalore to Pune dropped me somewhere near Telegaun which is near to Mumbai than Pune and I somehow managed to get back to Pune and reached Sayan and Chandan’s house. We were bunking together and there were more people about to come. I took some rest and then we were out , first stop was Reserved Bit , oh I can’t forget this place.

It is a perfect place for geeks and I loved every aspect of it. There I met Siddhesh for the first time we have had conversations over IRC though and met Nisha too. Amazing people the whole experience to travel to Reserved Bit and way back was amazing. We went to the venue to checkout where the camera will be and verify various aspects of the venue. After we came back I started working on the setup and man it was very tough and tricky to gather live feed from the camera.

First of all I was little hesitant to use any proprietary software but then I had no option so we somehow found a windows laptop and tried configuring it but almost everytime either we got a “BLUE SCREEN” or “UPDATES” which annoyed me , the sole reason of using windows was because we had a piece of hardware called capture cards, and the driver for which were not available. After long struggle and a lot of digging done by Siddhesh we got driver for Epiphan capture card for Linux and this was around 12 in the night and we all were still there at Reserved Bit. This gave all of us new hope and then it started we kind of got our minimalistic set up and Siddhesh did a “Compiler talk by Angle Fish” , it was a lot of fun by the time we got it working it was somewhere around 4 in the morning. After all this Sayan and Me actually took a walk back home and picked up Subho on the way. The next day CuriousLearner arrived and then Haseeb , Amit and Gaurav.

We were around 10 people squeezed in a single room but without any discomfort we kind of enjoyed our stay with occasional leg pulling to deep intense tech discussion the whole experience was just terrific. Then comes the actual venue setup that was one crazy thing so the video setup was working with Linux , we had Epiphan capture card working on Kernel version below 4.9 and OBS studio as a recording software. I actually spent a good number of hours to install OBS and downgrading kernel to 4.6 so that Epiphan driver works on at least 6 laptops. When we tried the setup on site and it broke because we didn’t take into account the audio from the mic. All of us were stuck in a state of panic then we realized that we have a mixer with us, but its power cord was left at Reserved Bit . By this time this setup kind of became our conference hack and we wanted it to work so badly. We actually ran back to Reserved Bit spent sometime there since we had some work and then quickly came back to the venue, connected the mixer and after few trial and run it worked.

“YES IT WORKED ” our efforts paid off, we recorded the whole conference using this setup, some of the recordings were a little glitchy and one other hack that we added was we weren’t recording the slides from speaker’s laptop we were doing it manually on our laptops. That means one copy of slide was being played on our laptops and we were recording it accordingly.

Apart from this experience I actually got the opportunity to meet all the keynote speaker the first so I met Nick, Honza, Terri,  John, Steven and Praveen. This was another experience in itself to know them and talk to the Rockstars of the FOSS WORLD.

As a speaker Kushal introduced me as the Speaker who is also the Cameraman for the event and that was may be the first time in a tech conference. Vivek and I have been collaborating over the talk for a long time and we figured out the order in which we need to speak and we spoke accordingly we kind of covered all the things that we wanted to and got a great response from the audience. I attended most of the talks since I was The A/V GUY but I had a huge help from rtnpro he was always there humble and ready to help.

The conference came to an end where Nisha told all the people about the effort that was put in from every person and specially Sayan. After this we had two days of devsprint where we had amazing projects, Vivek and I were mentoring for Pagure and we got a lot of new contributors and quite a number of PRs ( 13 to be precise ), the devsprint was a run away success.

I also got chance to interact with mbuf and man I saw him smile and crack jokes for the first time and it was crazy fun , ¬†I think it was the dinner after the last day of the conference. One of the most amazing experience was to talk to Haris and yes his name is Haris not Harish. The whole experience was so lovely that I don’t think that it can be better than this.

PS: We fixed my Macbook too

PPS: Video of our talk at PyCon Pune

Hacking on Pagure CI

Hacking on Pagure CI

“Ahaa!” I got a lot of ahaa moments when I was hacking on Pagure CI , ¬†Pagure CI’s initial draft was laid by lsedlar and I have blogged about it followed by me and Pingou. Pingou has done really amazing work with the flow and refactoring of code to making beautiful api calls.

I had great time hacking around it and got a bunch of learning. Few of the learning are :

  1. Try to do the minimal work in setting up the development environment mock everything that is available for testing.
  2. Think deeply about something when your mentor points it to you.

So the issue I was working on is a long pending one the issue was to attach build ID to all the Jenkins build Pagure was getting . Reason why attaching build id’s are necessary is to distinguish between different builds and to make the link to Jenkins a bit more specific for example if a build fail which was that build.

The first mistake I did was setting up Jenkins on my machine I had it previously but since my machine went under a kernel panic I lost all data related to Jenkins , now Fedora 25 has some packaging issue when installing ¬†Jenkins directly. But anyhow from Jenkins site I got a way to set it up and it worked for me. In the mean while Pingou was pointing it out that I actually don’t need Jenkins instance but I was not able to get him on that and I really feel bad about it.

After setting up Jenkins the other task for me was to configure it , which was really easy because I have done it before and also because it was well documented. For setting up the documentation is fine but for hacking on the CI you need a little less work.

Step 1

Set up REDIS on your machine , you can do that with installing redis using sudo dnf install redis and enable the service using sudo systemctl enable redis and then start the service using sudo systemctl start redis. Along with this you need to add config for redis in default_config.py or which ever config file you are giving to the server using --config. The configuration are well documented in pagure.cfg.sample.

Step 2

Now, copy the pagure-ci-server from pagure-ci directory into the parent directory. Now once you have done that , this step is necessary because this is the service that run for pagure-ci. Now you just have to run pagure-ci-server by python pagure-ci-server.py. Once this started your service will be up and running.

Step 3

Now you just fire up your instance and make a project , have two branches and open a PR form once branch to other, if you get some authentication error that is most probably because you not done the right permission for users to use Jenkins, this is not recommended but you can entirely turn off the security of Jenkins just because you are testing something.

If you have done everything correct you will see the Jenkins flag being attached to the Pull Request.

VERY IMPORTANT NOTE:

All this could be saved if I have just used python-jenkins to fetch a job from Fedora Jenkins instance and send it as a flag to my PR. Thank you Pingou for telling me this hack.

Happy Hacking!

Functional Programming 101

“Amazing!” ¬†that was my initial reaction when I heard and read about functional programming , I am very new to the whole concept so I might go a little off while writing about it so I am open to criticism . ¬†This is basically my understanding about functional programming and why I got hooked to it .

Functional Programming is a concept just like Object Oriented Programming , a lot of people confuse these concept and start relating to a particular language , thing that needs to be clear is languages are tools to implement concepts. There is imperative programming where you tell the machine what to do ? For example

  1. Assign x to y
  2. Open a file
  3. Read a file

While when we specifically talk about FP it is a way to tell how to do things ? The nearest example that I can come up with is SQL query  where you say something like

SELECT  * FROM Something where bang=something and bing=something

Here we didn’t tell what to do but we told how to do it. This is what I got as a gist of functional programming where we divide our task into various functional¬†parts and then we tell how things have to be implemented on the data.

Some of the core concepts that I came across was pure functions and functions treated as first class citizen or first class object . What each term means  lets narrow it down .

Pure functions  is a function whose return value is determined by the input given, the best example of pure functions are Math functions for example Math.sqrt(x) will return the same value for same value of x. Keeping in mind that x will never be altered. Lets go on a tangent and see that how this immutability of x is a good thing, this actually prevents data from getting corrupt.  Okay! That is alot to take in one go, lets understand this with a simple borrowed example from the talk I attended.

We will take example of a simple Library System¬† now for every library system there should be a book store, the book store¬†here is an immutable¬†data structure now what will happen if I want to add a new book to it ? Since it is immutable¬†I can’t modify it , correct ? So a simple solution to this problem is every time I add or remove a book I will actually deliver a new book store¬†and this new book store will replace the old one. That way I can preserve the old data because hey we are creating a whole new store. This is probably the gist or pros of functional programming.


book_store = ["Da Vinci's Code", "Angles and Demons", "The Lost Symbol"]
def add_book( book_store, book):
    new_book_store = []
    map(lambda old_book: new_book_store.append(old_book), book_store)
    new_book_store.append(book)
    return new_book_store

print add_book(book_store, "Inferno") # ["Da Vinci's Code", "Angles and Demons", "The Lost Symbol", "Inferno"]

print book_store # ["Da Vinci's Code", "Angles and Demons", "The Lost Symbol"]

In the above code you can actually see that a new book store is returned on addition of a new book. This is what a pure function looks like.

Function as first class citizens , I can relate a lot to this because of python where we say that everything is a first class objects. So, basically when we say functions are first class citizen we are implying that functions can be assigned to a variable, passed as a parameter and returned from a function. This is way more powerful then it sounds this bring a lot modular behavior to the software you are writing, it makes the project more organized and less tightly coupled. Which is a good thing in case you want to make quick changes or even feature related big changes.


def find_odd(num):
    return num if(num%2 != 0) else None

def find_even(num):
    return num if(num%2 == 0) else None

def filter_function(number_list, function_filter):
    return [num for num in number_list if(function_filter(num) != None)]

number_list = [1,2,3,4,5,6,7,8,9]
print filter_function(number_list, find_odd) # [1,2,5,7,9]
print filter_function(number_list, find_even) # [2,4,6,8]

In the above code you can see that function is passed as an argument to another function.

I have not yet explored into lambda calculus which I am thinking of getting into . There is a lot more power and beauty in functional programming.  I want to keep this post a quick read so I might cover some code example later, but I really want to demonstrate this code.


def fact(n, acc=1):
    return acc if ( n==1 ) else fact(n-1, n*acc)

where acc=1  this is pure textbook and really beautiful code which calculates factorial of n ,  when it comes to FP it is said To iterate is Human, to recurse is Divine. I will leave you to think more about it, will try to keep writing about things I learn.

Happy Hacking!

Vacation Of Code

Vacation Of Code

This all started when pingou gave me the opportunity to write a utility which helps to user to edit comment on pagure.Now for those who don’t know what pagure is , so pagure is open source equivalent of Github, to be precise :

Pagure is a light-weight git-centered forge based on pygit2. Currently, Pagure offers a web-interface for git repositories, a ticket system and possibilities to create new projects, fork existing ones and create/merge pull-requests across or within projects.

So the utility that was allotted to me was an edit button that privilege the owner of the comment to modify the comment on the pull request. That sounds really simple but writing the whole code and modifying others code are two different things.

I finally started exploring Flask and its feature so Flask is framework  that helps you write servers , Server as the name suggest is use to serve request.I had a brief idea about the type of request but never got the chance to explore it.

There are many types of request that help the client and server to talk to each other  famous ones are POST and GET.

The GET method

The GET method is the method used by the browser to ask the server to send back a given resource: “Hey server, I want to get this resource.” In this case, the browser sends an empty body. Because the body is empty, if a form is sent using this method, the data sent to the server is appended to the URL.

The POST method

The POST method is a little different. It’s the method the browser sends the server to ask for a response that takes into account the data provided in the body of the HTTP request: “Hey server, take a look at this data and send me back an appropriate result.” If a form is sent using this method, the data is appended to the body of the HTTP request.

Source: MDN

So in first attempt I wrote a shabby code and somehow make it work , but as I told it was really shabby so pingou and subho told me to use hidden form technique which is used to trigger certain functions without actually making the user know what is going on . It is more of a hack to get things done your way.The problem I faced was delete comment and edit comment use the same form to send request so both have the same end point hence inside the function that deletes comment I devised a way to distinguish how to differentiate when to edit comment and when to delete it.

The algorithm was simple get comment id , get new comment , replace the old comment by new one and make entry in the database.The code snippet that really helped me to understand things to a new depth was:

Example

Consider the following form:

<form action="http://foo.com" method="get">
  <input name="say" value="Hi">
  <input name="to" value="Mom">
  <button>Send my greetings</button>
</form>
With the GET method, the HTTP request looks like this:
GET /?say=Hi&to=Mom
HTTP/1.1 Host: foo.com
Example

Consider this form (the same one as above):

<form action="http://foo.com" method="post">
  <input name="say" value="Hi">
  <input name="to" value="Mom">
  <button>Send my greetings</button>
</form>

When sent using the POST method, the HTTP request looks like this:

POST / HTTP/1.1
Host: foo.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 13

say=Hi&to=Mom
 My Pull request is still under consideration so you can actually check what I did in pagure. Do let me know what you think about it.

DGPLUG SUMMER TRAINING

DGPLUG SUMMER TRAINING

This is  a place where you learn how to do stuff, I got to know about summer training when I was going through Twitter feeds. Bhibhas and Sayan tweeted about it and I thought why not give it a try. And now when I look back I made a wise decision joining it. Training generally take place over IRC so anyone can attend it irrespective of where are they from who are they and what is there background. I met a lot of amazing people I got to realize that how much more I need to do.

I started the training as a newbie , I tried to attend as many sessions as possible and most importantly I tried to implement what ever I learnt. I made amazing friends and found peers who can look into my code and we can have a discussion about issues. We had sessions form Kushal which was not only challenging but also fun.

We even had a session from mbuf which was enthralling and makes you ponder over your existence. He is one gem of a person. Sayan use to take class on python and basics of web development, he is one of the person whom I have bugged a lot and I still do but he has never given up on me.

Once a while there are guest sessions from people who are contributing to the upstream, these session actually motivate you towards contributing because they make you feel that all these that you are doing is not without a reason.

At the end people stop attending session I don’t know the reason but actually the doubles during the end because then only comes the real reason for the whole training. The end turns the trainees into contributors and that feeling cannot be converted into words. This training has not only taught me technologies but has given a direction to my life. Thank You DGPLUG.

FEDORA-INFRA: A contributor friendly repo

FEDORA-INFRA: A contributor friendly repo

This all started with zeal to contribute to open source. Seeing your code work is awesome but your code being used by zillions of people out there is not comparable.So it all started when Kushal gave the link to fedora-infra repo and Trishna shared the link to me. I went there and with the limited knowledge of python I have I thought I can contribute to the community.

I took up the ownership to fix an easyfix in the repo, pingou was the mentor for this bug and a super friendly one.I cloned the repo and set up my development environment now since was late but I was so damn interested to fix that bug that I worked for about two hours on it and I was able to get some result . All this while I was on irc on #fedora-apps channel. I pushed it and asked pingou to review it , but he slept. I thought I have to wait till the next day but then threebean and prth came to my rescue.

The reviewed my code and guided me and made me tweaked a little bit. Till now my commit count has reached 5. The next day pingou came online and made me tweak it a little more wait not a little but like crazy more after one more hour of work, the fix was done.

Now I have 8 commits , now the challenge was to squash 8 commits into 1 , I have never done it before and I ran into various issues but to my rescue me pingou was always there he guided me with every step. We tried for 3 hours approx and failed every time.

After that I tried one more time this time very slowly and steadily and there I was  SWEET SUCCESS , I sent a final PR and I think pingou was also online and he accepted it the very moment.The next day I sent another PR and it also got merged.I am really enjoying contributing to fedora-infra.Its just amazing .