Working with ButterKnife in Android


The following tutorial will help you understand Butter Knife implementation in Android

Why to use Butter Knife for Android?

Butter Knife in short is used in case for method binding of Android Views. Butter Knife is mainly used to make coding clean and simple especially in cases where where you deal with complex layout. Usually if you aren’t using Butter Knife you’ll have to eventually use findViewById() method for each view that you create in your layout, in cases where your application deals with many TextView’s, EditText’s, Button’s , ImageView’s the lines of code you write extends. In such cases Butter Knife comes in handy, using which you can reduce many lines of code and simply avoid methods such as findViewById().

Does Butter Knife make your App to slow down ?

No. Butter Knife doesn’t slow down your App, it gives the same result as when you declare your views using findViewById. The reason behind it is ButterKnife automatically generates findViewById calls at compile time itself thus, making use of “Annotation Processing”.

Butter Knife in Action :

Usage in xml :


android:hint="First Name"

Usage in Java class.
LinearLayout linearLayout;
EditText edittext;
//Just use the below code for setting a OnclickListener. That’s it. you don’t need to use findViewById multiple times
void OnLayoutClicked(View view) {
//Do Your Stuff here

Learn more about butterknife at :

sTeam GSoC 2016 Windup

(ˢᵒᶜⁱᵉᵗʸserver) aims to be a platform for developing collaborative applications.
sTeam server project repository: sTeam.
sTeam-REST API repository: sTeam-REST

An overview of the work done by ajinkya007 during Google Summer of code 2016 with FOSSASIA on its project sTeam.

The community bonding period saw the creation of a docker image and a debian package for the sTeam server. The integration of the sTeam shell into vi, improvements in the export and import to git scripts, user and group manipulation commands, sending mails through the commandline, viewing logs and the edit script modifications were done subsequently. The later part of GSOC saw that the sTeam-rest repository was restructured, unit and api-end point tests were performed. The new web interface developed was tested.
The code written during this period by me and siddhant was merged and the conflicts were resolved. The merged code was tested thoroughly as no automated test integration tool supports pike programming language. Documentation was generated using Doxygen and deployed in the gh-pages of the sTeam server repository.

A trello board was maintained throughout the course of GSOC 2016.

Trello Board: sTeam


Issues Reported and Resolved

A list of tasks covered and all the Pull requests related to each:

Tasks Issue PR
Make changes in the Makefile for installation of sTeam. Issue-25 Issue-27 PR-66 PR-67
Edit script modifications Issue-20 Issue-29 Issue-43 PR-44 PR-48
Indentation of output in steal-shell. Issue-24 PR-42
Integrate steam-shell into vim or emacs. Issue-37 Issue-43 Issue-49 PR-41 PR-48 PR-51
Improve the import and export from git scripts. Issue-9 Issue-14 Issue-16 Issue-18 Issue-19 Issue-46 PR-45 PR-54 PR-55 PR-76
Create, Delete and List the user through commandline Issue-58 Issue-69 Issue-72 PR-59 PR-70 PR-78
Sending Mails through commandline Issue-74 PR-85
Generate error logs and display them in CLI Issue-83 PR-86
Create a file of any mime type from command line. Issue-79 PR-82
Add more commands for group operations. Issue-80 PR-84
Add more utility to the steam-shell Issue-56 Issue-71 Issue-73 PR-57 PR-75 PR-81
Restructure the sTeam-rest repository List of Issue’s List of PR’s
Write test cases to test sTeam-rest api List of Issue’s List of PR’s
Create a debian package and a docker image for easy deployment Create docker image Docker Image
Document the work done Issue 149 sTeam Server Structure, sTeam Server Documentation
Test the web-interface

Commits Merged

During the course of GSOC 2016, work was done on the sTeam and sTeam-rest repositories.

1. The work done on the sTeam repository.

We have combined all the work into two branches for the ease of creating a debian package. The commits made by me in each branch can be seen here.

2. The work done on the sTeam-rest repository

The push request’s sent for the issue’s are yet to be merged in the main repository. The list of PR’s for the sTeam-rest repository.

sTeam-rest PR’s

The weekly blogs

The blogs summarizing the work done during the week were published on my personal website. These can be found on Weekly Blogs
All the blogs can also be found on the Fossasia blog.
The list in reverse chronological order is as follows.


Scrum reports were posted on the #steam-devel on and sTeam google group. The sTeam trello board also has everyday scrum reports.

Further Improvements

  1. sTeam command line lacks the functionality to read and set the object access permissions. sTeam function analogous to getfacl() to change the sTeam server object permisssions.
  2. sTeam debian package for easy installation of the sTeam server. The debian package is yet to be fully packaged.

Special Thanks

  • I would like to thank my mentors Mario Behling, Hong Phuc Dang, Martin Bahr, Trilok Tourani and my peers for being there to help me and guide me.
  • I would like to thank FOSSASIA, sTeam and Pike Community for giving me this opportunity and guiding me in this endeavour.
  • I would also like to thank Google Summer of Code for this experience.

Feel free to explore the repository. Suggestions for improvements are welcomed.

Checkout the FOSSASIA Idea’s page for more information on projects supported by FOSSASIA.

KISS Datatable

Recenlty I’ve faced a problem with sorting columns in Datatable.

What is Datatable?

Datatable is a plug-in for Jquery library. It provides a lot of features like pagination, quick search or multi-column ordering. Besides, you can develop easily Bootstrap or Foundation ui css styles. There are also more other option but It doesn’t make sense to list it here, because you can visit their site and you can read clearly documentation. On Datatable website you can see a lot of examples. First of them shows how to improve your ordinary table to awesome and rich of features table. One function changes everything, It’s fantastic!  


Returning to my problem which I’ve faced, as I told it was problem related to sorting column in table.

I know sorting is a trivial thing. I hope that everyone knows it 🙂 Sorting by a date is also implemented in a datatable library. So everything is clear when we don’t change date format to human readable format. I mean something like this ‘3 hours ago’, ‘1 year ago’.

When Open Event team tested how datatable manages ordering columns in that format it didn’t work. It’s quite hard to sort by that format, So I’ve invented an idea. Surely you are wondering what i’ve invented. I’ve postponed my minds about sort by this values. It can direct to overwork. When I thought about it, weird ideas came to my mind, a lots of conditions, If statements… Therefore I’ve resigned from this. I’ve used KISS principle. KISS means ‘keep it simple stupid’. I like it!

Therefore that sorting is implemented on frontend side. I’ve decided not to display human readable date format at the beginning. I find  all dates which have format “YYYY-MM-DD HH:mm” then I replace that format to human readable format. So it’s very quick and comfortable, and doesn’t require a lot conditions to write. Of course I’ve tried to implement it in Datatable library. I suppose that it would  require more effort than it’s now.

Below You can see great function which changes a date in frontend side but does not change data in a datatable. So sorting process takes place in a datatable using format  “YYYY-MM-DD HH:mm” but user see human readable format. Isn’t it awesome?!

function change_column_time_to_humanize_format(datatable_name, column_id) {
  $(datatable_name).each(function( key, value ) {
    $(value).children().each(function( key1, value2 ) {
       if(key1 === column_id ){
          var current_value = $(value2).text().slice(0, 16);
          var changed_value = moment(current_value, "YYYY-MM-DD hh:mm").fromNow()
          var isValid = moment(current_value, "YYYY-MM-DD HH:mm", true).isValid()
          if (changed_value !== current_value && isValid === true){


sTeam Docker Image

(ˢᵒᶜⁱᵉᵗʸserver) aims to be a platform for developing collaborative applications.
sTeam server project repository: sTeam.
sTeam-REST API repository: sTeam-REST


What is Docker?

Docker is open source software to pack, ship and run any application as a lightweight container. Containers are completely hardware and platform independent so you don’t have to worry about whether what you are creating will run everywhere.

In order to facilitate development in all the environments and give the user the ease from the cumbersome installation steps a docker image was made for the sTeam project.
This docker image contains all the necessary dependencies to start the sTeam server.
It also includes the sTeam UI and the Rest API along with it’s dependencies. These have already been installed and developer can start collaborating to it.


The docker image can be found at :

It has all the necessary information for it’s usage and installation.

The dockerfile for the sTeam repository:

FROM ubuntu:latest
RUN apt-get update
RUN apt-get install -y wget git firefox nodejs nodejs-legacy npm
RUN apt-get install -y build-essential mysql-server libmysqld-dev bzip2 libjpeg$
RUN apt-get install -y pike7.8 pike7.8-bzip2 pike7.8-svg
RUN apt-get install -y libxml2-dev libxslt1-dev automake flex
RUN npm install -g npm bower gulp coffee-script jasmine-node frisby
RUN cd home
RUN wget -c$
RUN git clone
RUN cd sTeam
RUN git checkout societyserver-source
RUN ./build
RUN sudo ./install
RUN cd ..
RUN git clone
RUN cd sTeam-web-interface-gsoc-2015
RUN npm install
RUN cd ..
RUN git clone
RUN cd steam-rest
RUN npm install

Feel free to explore the repository. Suggestions for improvements are welcomed.

Checkout the FOSSASIA Idea’s page for more information on projects supported by FOSSASIA.

Python code examples

I’ve met many weird examples of  behaviour in python language while working on Open Event project. Today I’d like to share some examples with you. I think this knowledge is necessary, if you’d like to increase a  bit your knowledge in python area.

Simple adding one element to python list:

def foo(value, x=[]):
  return x

>>> print(foo(1))
>>> print(foo(2))
>>> print(foo(3, []))
>>> print(foo(4))


[1, 2] 
[1, 2, 4]

First output is obvious, but second not exactly. Let me explain it, It happens because x(empty list) argument is only evaluated once, So on every call foo(), we modify that list, appending a value to it. Finally we have [1,2, 4] output. I recommend to avoid mutable params as default.

Another example:

Do you know which type it is?

>>> print(type([ el for el in range(10)]))
>>> print(type({ el for el in range(10)}))
>>> print(type(( el for el in range(10))))

Again first and second type are obvious <class ‘list’>, <class ‘set’>. You may  think that last one should return type tuple but it returns a generator <class ‘generator’>.


Do you think that below code returns an exception?

list= [1,2,3,4,5]
>>> print(list [8:])

If you think that above expression returns index error you’re wrong. It returns empty list [].

Example funny boolean operators

>>> 'c' == ('c' or 'b')
>>> 'd' == ('a' or 'd')
>>> 'c' == ('c' and 'b')
>>> 'd' == ('a' and 'd')

You can think that that OR and AND operators are broken.

You have to know how python interpreter behaves while looking for OR and AND operators.

So OR Expression takes the first statement and checks if it is true. If the first statement is true, then Python returns object’s value without checking second value. If first statement is false interpreter checks second value and returns that value.

AND operator checks if first statement is false, the whole statement has to be false. So it returns first value, but if first statement is true it checks second statement and returns second value.

Below i will show you how it works

>>> 'c' == ('c' or 'b')
>>> 'c' == 'c'
>>> 'd' == ('a' or 'd')
>>> 'd' == 'a'
>>> 'c' == ('c' and 'b')
>>> 'c' == 'b'
>>> 'd' == ('a' and 'd')
>>> 'd' == 'd'

I hope that i have explained you how the python interpreter checks OR and AND operators. So know above examples should be more understandable.

sTeam Server Object permissions and Doxygen Documentation

(ˢᵒᶜⁱᵉᵗʸserver) aims to be a platform for developing collaborative applications.
sTeam server project repository: sTeam.
sTeam-REST API repository: sTeam-REST

sTeam Server object permissions

sTeam command line lacks the functionality to read and set the object access permissions. The permission bits are: read,write, execute, move, insert,
annotate, sanction. The permission function was designed analogous to the getfacl() command in linux. It should display permissions as: rwxmias corresponding to the  permission granted on the object.

The the key functions are get_sanction, which returns a list of objects and permissions and sanction_object, which adds a new object and its set of permissions. The permissions is stored as an integer and the function should break the individual bits like getfact().

The permission bits for the sTeam objects are declared in the

// access.h: The permission bits

#define FAIL           -1 
#define ACCESS_DENIED   0

#define SANCTION_READ          1
#define SANCTION_EXECUTE       2
#define SANCTION_MOVE          4
#define SANCTION_WRITE         8
#define SANCTION_INSERT       16
#define SANCTION_ANNOTATE     32

The get_sanction method defined in the access.pike returns a mapping which has the ACL(Access Control List) of all the objects in the sTeam server.

// Returns the sanction mapping of this object, if the caller is privileged
// the pointer will be returned, otherwise a copy.
final mapping
    if ( _SECURITY->trust(CALLER) )
	return mSanction;
    return copy_value(mSanction);

The functions gets the permission values which are set for every object in the server.

The sanction_object method defined in the object.pike sets the permissions for the new objects.

// Set new permission for an object in the acl. Old permission are overwritten.
int sanction_object(object grp, int permission)
    ASSERTINFO(_SECURITY->valid_proxy(grp), "Sanction on non-proxy!");
    if ( query_sanction(grp) == permission )
      return permission; // if permissions are already fine

    try_event(EVENT_SANCTION, CALLER, grp, permission);
    set_sanction(grp, permission);

    run_event(EVENT_SANCTION, CALLER, grp, permission);
    return permission;

This method makes use of the set_sanction which sets the permission onthe object. The task ahead is to make use of the above functions and write a sTeam-shell command which would provide the user to easily access and change the permissions for the objects.

Merging into the Source

The work done during GSOC 2016 by Siddhant and Ajinkya on the sTeam server was merged into the gsoc201-societyserver-devel and gsoc2016-source branches in the societyserver repository.
The merged code can be found at:

The merged code needs to be tested before the debian package for the sTeam server is prepared. The testing has resulted into resolving of minor bugs.

Doxygen Documentation

The documentation for the sTeam is done using doxygen. The doxygen.pike is written and used to make the documentation for the sTeam server. The Doxyfile which includes the configuration for generating the sTeam documentation is modified and input files are added. The generated documentation is deployed on the gh-pages in the societyserver/sTeam repository.
The documentation can be found at:

The header files and the constants defined are also included in the sTeam documentation.

sTeam Documentation:


sTeam defined constants:


sTeam Macro Definitions:


Feel free to explore the repository. Suggestions for improvements are welcomed.

Checkout the FOSSASIA Idea’s page for more information on projects supported by FOSSASIA.

Accepting Stripe payments on behalf of a third-party

{ Repost from my personal blog @ }

In Open Event, we allow the organizer of each event to link their Stripe account, so that all ticket payments go directly into their account. To make it simpler for the organizer to setup the link, we have a Connect with stripe button on the event creation form.

Clicking on the button, the organizer is greeted with a signup flow similar to Login with Facebook or any other social login. Through this process, we’re able to securely and easily obtain the credentials required to accept payments on behalf of the organizer.

For this very purpose, stripe provides us with an OAuth interface called as Stripe Connect. Stripe Connect allows us to connect and interact with other stripe accounts through an API.

We’ll be using Python’s requests library for making all the HTTP Requests to the API.
You will be needing a stripe account for this.

Registering your platform
The OAuth Flow

The OAuth flow is similar to most platforms.

  • The user is redirected to an authorization page where they login to their stripe account and authorize your app to access their account
  • The user is then redirected back to a callback URL with an Authorization code
  • The server makes a request to the Token API with the Authorization code to retrieve the access_token, refresh_token and other credentials.

Implementing the flow

Redirect the user to the Authorization URL.  

The authorization url accepts the following parameters.

  1. client_id – The client ID acquired when registering your platform.required.
  2. response_type – Response type. The value is always code. required.
  3. redirect_uri – The URL to redirect the customer to after authorization.
  4. scope – Can be read_write or read_only. The default is read_only. For analytics purposes, read_only is appropriate; To perform charges on behalf of the connected user, We will need to request read_write scope instead.

The user will be taken to stripe authorization page, where the user can login to an existing account or create a new account without breaking the flow. Once the user has authorized the application, he/she is taken back to the Callback URL with the result.

Requesting the access token with the authorization code

The user is redirected back to the callback URL.

If the authorization failed, the callback URL has a query string parameter error with the error name and a parameter error_description with the description of the error.

If the authorization was a success, the callback URL has the authorization code in the code query string parameter.

import requests

data = {  
    'client_secret': 'CLIENT_SECRET',
    'grant_type': 'authorization_code'

response ='', data=data)

The client_secret is also obtained when registering your platform. The codeparameter is the authorization code.

On making this request, a json response will be returned.

If the request was a success, the following response will be obtained.

  "token_type": "bearer",
  "stripe_publishable_key": PUBLISHABLE_KEY,
  "scope": "read_write",
  "livemode": false,
  "stripe_user_id": USER_ID,
  "refresh_token": REFRESH_TOKEN,
  "access_token": ACCESS_TOKEN

If the request failed for some reason, an error will be returned.

  "error": "invalid_grant",
  "error_description": "Authorization code does not exist: AUTHORIZATION_CODE"

The access_token token obtained can be used as the secret key to accept payments like discussed in Integrating Stripe in the Flask web framework.

CommonsNet’s main features are ready

Main CommonsNet features are generating a file and  generating a code script. Today I would like to provide you with a simple and short guideline how I have managed to implement them.

Generate a file

Generating a file is the most important feature of our website, and it is not only a condition of its existance but also a basis to find stakeholders – in general people who want to use CommonsNet webiste.  It is the most complicated CommonsNet feature as well even if it is not so difficult as you may think.

To implement this feature a pure JavaScript is used and for now we have chosen the simplest solution to build it, mainly because we need to have a working webiste now to start a real promotion and find many customers.

Important steps here are:

  1. Manually prepare a .fodt file
  2. Get .fodt file and modify it
  3. Generate a pdf file from a ready .fodt file
  4. Write function to download a pdf file.


Preparing .fodt file

My mentor Andre Rebentisch has recommended me to use .fodt file because it’s very user-friendly and let you to prepare a file’s structure very easy. Actually that’s it! I have prepared manually in Libre Office a default doc file, and then save it in .fodt extension. .Fodt is a great option because it behaves as .xml file and let you modify this file using any programming language.

So, as I have already mentioned above I have created a simple doc file and prepare the structure. It is very clear and looks like a default Libre Office file. Only thing is that it has .fodt extension which means that you can open it in a code editior like for e.g. Sublime and start modifying easily.

If you open your .fodt file in a Sublime, it looks like this. Isn’t it simply? And above all it helps you to easily manipulate your data using for e.g a JavaScript.

Screen Shot 2016-08-13 at 17.19.06

Screen Shot 2016-08-13 at 17.18.00Get .fodt file to manipulate it

In my AngularJS Wizard Controller I write a function to get data from my .fodt file

 method: 'GET',
 url: '',
 }).success(function(data){}) .error(function(){

It’s very easy code sample and you can find it in many Internet resources. I hope it is understandable to you as well. I have written a function which get a .fodt file and return data. Inside .success I have written my whole code to manipulate a .fodt file.  To use it I have decided to use a simple JavaScript replace method and if-else conditions, and in dependence on user’s inputs in a wizard form create different file’s structures. Let me show you a small section :

result = result.replace("NETWORK_NAME", "The owner provides" + " " + vm.ssid + "network connection")

if ((vm.password !== "") && (typeof vm.password !== "undefined")) {
 result = result.replace("INPUT_PASSWORD", "The owner informs that password is" + " " + vm.password);


Generate a pdf file from a ready .fodt file

It is still in progress! I will update it as soon as I manage to successfully implement it!

Write function to save it

To save my ready file I have used save function() and put in my AngularJS Wizard Controller.

$ = function() {}

Generate a code script

We have decided to implement a generating code feature, because we want our users to be able to simply fill a wizard form with all Wifi details, then copy  a generated code  and be able to simply  paste it to their website.

We believe it is a very convenient solution to them because all they need to do it is to go through a form and it is ready. Besides, we have already decided to get rid of a database and use only a JSON file to not complicate our website’s working. So, that’s also the reason why we want to make it as simple as possible.

That’s why I have decided to create a link snd store there all wizard form’s values Undoubtedly it causes to build a very long link, but in the same time I believe that it is a good solution if we don’t use a database. I have also already found some ways to shorten and encrypt the generated link.

In my WizardController AngularJS I have write a function with a condtion

$scope.gotoStep = function(newStep) {
 currentStep = newStep;
 if ( currentStep === 3) {
 var link = "" + vm.ssid + "&password=" + vm.password + "&security=" + vm.securitytypes + "&standard=" + vm.wifistandards + "&payment=" + vm.paymentfieldyes + "&fee=" + vm.paymentfield + "&timelimit=" + vm.timelimityes + "&limit=" + vm.timelimitfield + "&service=" + vm.serviceyes + "&specialdevices=" + vm.specialdevices + "&devices=" + vm.specialdevicesfield + "&specialsettings=" + vm.specialsettings + "&settings=" + vm.specialsettingsfield + "&acceptterms=" + vm.acceptterms + "&liking=" + vm.socialprofile + "&downloading=" + vm.downloading + "&restrictions=" + + "&country=" + vm.countries + "&law=" + vm.legalrestrictions
 vm.code = '<a href="' + link + '">CommonsNet</a>'

If my currentStep === 3 (actually it’s a  confirmation.html templateUrl) I create a link (a code) which is available to users to copy and paste to their website.

Then I have also created a new FileController (FileCtrl) which is called when users enter a (if they paste in an url a copied generated link)

app.controller('FileCtrl',['$scope', '$routeParams', function ($scope, $routeParams) { $scope.ssid = $routeParams.ssid; $scope.password = $routeParams.password; }])

Finally I have created a .html structure to post data from a wizard from which are all stored in our link. It’s a normal html structure but in order to adjust the html’s content to user’s wizard inputs I have used an Angular ng-if . A little example looks like this:

ng-if="ssid && ssid != 'undefined'

And that’s it. It still needs some improvements and fixing bugs but main features work according to my plan!!!

It’ time to intensively extend the idea of CommonsNet and find stakeholders! Are you interested too? I am sure you are, because CommonsNet is a great tool which helps us to build a transparent Wifi networks!

Feel free to write your comments and suggestion!

PayPal Express Checkout in Python

As per the PayPal documentation …

Express Checkout is a fast, easy way for buyers to pay with PayPal. Express Checkout eliminates one of the major causes of checkout abandonment by giving buyers all the transaction details at once, including order details, shipping options, insurance choices, and tax totals.

The basic steps for using express checkout to receive one-time payments are:

  1. Getting the PayPal API credentials.
  2. Making a request to the API with the transaction details to get a token
  3. Using the token to send the users to the PayPal payment page
  4. Capturing the payment and charging the user after the user completes the payment at PayPal.

We will be using PayPal’s Classic NVP (Name-value pair) API for implementing this.

Getting PayPal API Credentials

To begin with, we’ll need API Credentials.
We’ll be using the Signature API credentials which consists of

  • API Username
  • API Password
  • Signature

To obtain these, you can follow the steps at Creating and managing NVP/SOAP API credentials – PayPal Developer.

You’ll be getting two sets of credentials. Sandbox and Live. We’ll just stick to the Sandbox for now.

Now, we need sandbox test accounts for making and receiving payments. Head over to Creating Sandbox Test Accounts – PayPal Developer and create two sandbox test accounts. One would be the facilitator and one would be the buyer.

PayPal NVP Servers

All the API actions will take place by making a request to the PayPal server. PayPal has 4 different NVP servers for 4 different purposes.

  1. – Sandbox “testing” server for use with API signature credentials.
  2.– PayPal “live” production server for use with API signature credentials.
  3. – Sandbox “testing” server for use with API certificate credentials.
  4. – PayPal “live” production server for use with API certificate credentials.

We’ll be using the Sandbox “testing” server for use with API signature credentials.

Creating a transaction and obtaining the token

To create a transaction, we’ll need to make a request with all the transaction details. We can use Python requests library to easily make the requests. All requests are POST.

We’ll be calling the SetExpressCheckout method of the NVP API to obtain the token.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'SetExpressCheckout',
    'VERSION': 93,
    'RETURNURL': 'http://localhost:5000/paypal/return/',
    'CANCELURL': 'http://localhost:5000/paypal/cancel/'
response ='', data=data)  
token = dict(urlparse.parse_qsl(response.text))['TOKEN']


  • USER represents your Sandbox API Username.
  • PWD represents your Sanbox API Password.
  • SIGNATURE represents your Sandbox Signature.
  • SUBJECT represents the facilitator’s email ID.
  • PAYMENTREQUEST_0_AMT is the total transaction amount.
  • PAYMENTREQUEST_0_CURRENCYCODE is the 3 digit ISO 4217 Currency code.
  • RETURNURL is where the user will be sent to after the transaction
  • CANCELURL is where the user will be sent to if he/she cancels the transaction.

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

From the response, we’re extracting the TOKEN which we will use to generate the payment URL for the user.

This token has to be retained since we’ll be using it in further steps of the process.

Redirecting the user to PayPal for Approval

With the token we obtained, we can form the payment URL.<TOKEN>

We’ll have to send the user to that URL. Once the user completes the transaction at PayPal, he/she will be returned to the RETURNURL where we’ll further process the transaction.

Obtaining approved payment details and capturing the payment

Once the user completes the transaction and gets redirected back to RETURNURL, we’ll have to obtain the confirmed payment details from PayPal. For that we can again use the token ID that we obtained before.

We’ll now be making a request to the GetExpressCheckoutDetails method of the API.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'GetExpressCheckoutDetails',
    'VERSION': 93,

response ='', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
payerID = result['PAYERID']

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

This will provide us with information about the transaction such as transaction time, transaction amount, charges, transaction mode, etc.

But, we’re more interested in the PAYERID which we’ll need to capture/collect the payment. The money is not transferred to the facilitators account until it is captured/collected. So, be sure to collect it.

To collect it, we’ll be making another request to the DoExpressCheckoutPaymentmethod of the API using the token and the PAYERID.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'DoExpressCheckoutPayment',
    'VERSION': 93,
    'PAYERID': payerID,

response ='', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
status = result['ACK']

All the details have to be the same as the ones provided while obtaining the token. Once we make the request, we’ll again get a URL-Encoded, Name-value pair response. We can decode that into a dict by using Python’s urlparsemodules.

From the response, ACK (Acknowledgement status) will provide us with the status of the payment.

  • Success — A successful operation.
  • SuccessWithWarning — A successful operation; however, there are messages returned in the response that you should examine.
  • Failure — The operation failed; the response also contains one or more error messages explaining the failure.
  • FailureWithWarning — The operation failed and there are messages returned in the response that you should examine.

And, we have completed the PayPal transaction flow for Express Checkout. These are just the basics and might miss a few stuff. I suggest you go through the following links too for a better understanding of everything:

For Reference:
  1. PayPal Name-Value Pair API Basics – PayPal Developer
  2. How to Create One-Time Payments Using Express Checkout – PayPal Developer

Writing linux commands

sTeam includes a number of tools namely steam-shell, debug, edit, import and export from git. These tools are only accessible from the tools folder in the sTeam installation. My task is to make a steam command for linux so that all these tools can be accessible from anywhere just like any other linux application.


The command structure decided is that we have a global sTeam command and sub commands for each of the tools. This structure can be though of as similar to the structure of the git command. The central git command has many sub commands like branch, checkout, reset, merge, etc. I started with making a pike executable and then changing the installation files to copy this executable to /usr/bin. Now this pike executable becomes accessible from anywhere in the system and acts like a linux command.

I wrote the main function to accept the command line arguments and passed them to a function named resolveParam. In this function I am using an if-else structure to segregate the different sub commands. For shell and debug I started a child process to execute the file for these tools present in /usr/local/lib/steam/tools. The following code snippet gives an example.

void resolveParam(int argc,array(string) argv)
array command =({"/usr/local/lib/steam/tools/steam-shell.pike"});
object shell = Process.create_process(command, (["stdin":Stdio.stdin,"stdout":Stdio.stdout,"stderr":Stdio.stderr]));

I had some problem when I had to accept more arguments than just the sub command. Foe example the edit command works as ./edit <filename1> <filename2> <filename3>… Using the global command it becomes steam edit <filename1> <filename2> <filename3>… I had to pass all the rest of the arguments to the edit scripts. I had to add them in the command array. The first solution would be to loop through the arguments array and add them all, however pike has a very easy and elegant way of doing it in one sentence.

array command = ({"/usr/local/lib/steam/tools/edit.pike"})+argv[2..];

This gets our global command up and running. Rest of the time I spend on resolving merge conflicts while merging all my previous Pull Requests.

linux command
output showing the use of steam command