Lets start by dividing the posts that a person makes into two wide categories -

1) Personal posts – Like uploading an album or updating status which says something about oneself like “Having fun time at Goa, boozing and beaches!”

2) Non Personal posts – These include some generic updates like “Sachin’s career in an infographic”.

Now we need to divide people in friends list and set a “Like expectation” with each group. Its more like probability of getting a like from that group of people. Here is how I divide people in friends list -

a) People with whom you are in regular touch – These are people like your family, friends with whom you go out every weekend, people with whom you chat regularly, girlfriend/boyfriend etc. “Like expectation” in this case would be high. Lets keep it at 0.8 for personal posts as well as non personal posts.

b) People with whom you talk less frequently – These are people like your office colleagues, few relatives, some “not so good” friends, etc. “Like expectation” in this case should be around 0.3 for personal posts and 0.4 for non personal posts.

c) People to whom you rarely talk – These include few batch mates from graduate school, few school mates, distant relatives, etc. “Like expectation” in this case would be very low. Lets keep it at 0.1 for personal posts and 0.3 for non personal posts.

One important point to note here would be the variation in “Like expectation” from a) to b) to c). It doesn’t vary much in case of non personal posts, as expected, because if you share “Sachin’s career in an infographic”, then everyone sharing that interest would be equally interested in that post irrespective of your relation with that person. On the other hand, “Like expectation” varies a lot (goes down steeply) as one moves from a) to b) to c). This is more obvious as your relation with person is getting weaker and he would be less interested in your personal posts as you go from a) to b) to c).

These “Like expectation” values have been taken approximately, but actually they should be based on a survey. So, for a person with 250 Facebook friends and if 20, 30 and 200 are the number of people in categories a), b) and c) respectively, then he should be getting -

20*0.8 + 30*0.3 + 200*0.1 = 16 + 9 + 20 = 45 likes approximately if he posts a personal stuff, and

20*0.8 + 30*0.4 + 200*0.3 = 16 + 12 + 60 = 88 like approximately if he posts a non personal stuff.

1) Go to Google Reader –> Reader Settings.

2) Click on Import/Export. Then click on “Download your data through Takeout”

3) This will take you to the Takeout page. Here if you have more than one services, choose Reader and click on “Create Archive”.

4) In the Downloads tab, you will see the Takeout download getting generated. Download and save the file.

5) In the downloaded file, look for subscriptions.xml. This is the file you would need to import your data to The Old Reader.

6) Now go to The Old Reader and login. Click on Import.

7) Now browse for the subscriptions.xml from point 5 and click on Import.

You are done. Most probably you will see a long queue of imports before you. That is expected as many people are switching to this service.

As I move on with the course and complete assignments I’m thinking of putting together all the commands with easy explanations here in my blog. As I can see that although there have been few videos on using Octave but for an absolute beginner, there is still something lacking and most people won’t get the hold of Octave properly. I would be creating this series in parts and in each part I would collect and explain few commands every time. So here are the commands for this part -

1) Matrix Transpose -

If M is the given matrix, then matrix transpose can be obtained by M’ -

octave:19> M = [1 2 3; 4 5 6; 7 8 9];
octave:20> M’
ans =

   1   4   7
   2   5   8
   3   6   9

2) Obtain a particular row from the matrix -

Suppose you have a matrix M and you want to get the second row of the matrix, you should use M(2,:)

This means that you want to take all(represented by : ) the elements present in the second row which effectively means whole of second row -

octave:21> M = [1 2 3; 4 5 6; 7 8 9];
octave:22> M(2,:)
ans =

   4   5   6

3) Obtain a particular column from the matrix -

Suppose you have a matrix M and you want to get the first column of the matrix, you should use M(:,1)

This means that you want to take all(represented by : ) the elements present in the first column which effectively means whole of first column -

octave:23> M = [1 2 3; 4 5 6; 7 8 9];
octave:24> M(:, 1)
ans =

   1
   4
   7

4) Obtain a particular element from the matrix -

From 2) and 3) its pretty clear that to get an element i,j from a matrix M, you need to invoke M(i, j) -

octave:25> M = [1 2 3; 4 5 6; 7 8 9];
octave:26> M(2,1)
ans =  4

5) Creating simple for loop -

0:4 shows the loop goes from 0 to 4 with interval of 1

octave:29> for i = 0:4
> 2^i
> end
ans =  1
ans =  2
ans =  4
ans =  8
ans =  16

6) Creating plots with some simple options -

Following creates a simple line plot of values of y against x -

octave:32> x = [1 2 3 4 5 6 7 8 9 0];
octave:33> y = [3 6 9 2 7 5 1 0 4 4];
octave:34> plot(x,y)

Some simple options that can be added are -

The following command would create plot marks as blue o’s-

octave:41> plot(x, y, ‘bo’)

If you want to increase the plot marks, you can do so by using ‘MarkerSize’ -

octave:47> plot(x, y, ‘bo’, ‘MarkerSize’, 15)

You can set the labels for X and Y axis using xlabel and ylabel respectively -

xlabel(‘Label for X’);

ylabel(‘Label for Y’);

That’s all for this part. Happy Octaving

Objective – To implement a Facebook login system for authentication. If you are still unsure what I’m talking about and want to see the demo, just go to http://social.matiasaguirre.net/ and click Facebook.

Package – Download the package from https://github.com/omab/django-social-auth or direct zip url – https://github.com/omab/django-social-auth/archive/master.zip

Unzip the package, go to package directory and run the following command to install it -

python setup.py install

or, if you have pip installed, then you don’t need to download the package separately, simply use -

pip install django-social-auth

Now you need to associate a Facebook app with this authentication system to make it work. Go to https://developers.facebook.com/apps and create an app. We need not do anything fancy here. We just need two values from this app – “App ID/API Key” and “App Secret”.

Now lets go to the core Django web application part -

1) Go to settings.py add the following in the INSTALLED_APPS -

‘social_auth’

2) Now we need to add few more settings for this authentication system. In the same file add the following -

AUTHENTICATION_BACKENDS = (
    ‘social_auth.backends.facebook.FacebookBackend’,
    ‘django.contrib.auth.backends.ModelBackend’,
)

TEMPLATE_CONTEXT_PROCESSORS = (
    ‘django.contrib.auth.context_processors.auth’,
    ‘social_auth.context_processors.social_auth_by_type_backends’,
)

SOCIAL_AUTH_ENABLED_BACKENDS = (‘facebook’,)
SOCIAL_AUTH_DEFAULT_USERNAME = ‘new_social_auth_user’

FACEBOOK_APP_ID = <Put value of App ID/API Key from the Facebook app>
FACEBOOK_API_SECRET = ‘<Put value of App Secret from the Facebook app>

LOGIN_URL = ‘/login/’
LOGIN_REDIRECT_URL = ‘/polls/’
LOGIN_ERROR_URL = ‘/login-error/’

 

Make sure to set proper values of “LOGIN_URL”(login page where the Facebook authentication page would come) and “LOGIN_REDIRECT_URL”(page to redirect to after authentication). They might be different in your case.

3) Now to reflect the changes we did to setting.py to the database, run -

python manage.py syncdb

4) Now add the following to urls.py -

from django.views.generic.simple import redirect_to

and in “urlpatterns” in urls. py add -

url(r”, include(‘social_auth.urls’)),

url(r’^login/$’, redirect_to, {‘url’: ‘/login/facebook’}),

There is one last thing I want to point out here is that “LOGIN_REDIRECT_URL” should be set equal to the value of “Canvas URL” in the Facebook app. To look and change the value of “Canvas URL” in the Facebook app, go to the app and click on “Edit App”. In “Settings” –> “Basic”, you will see “Canvas URL”. Change it to match the value of “LOGIN_REDIRECT_URL” else you will get the following error -

API Error Code: 191
API Error Description: The specified URL is not owned by the application
Error Message: Invalid redirect_uri: Given URL is not allowed by the Application configuration.

Now run your server and goto /login/ and you will see a nice Facebook authentication page for your web app

Although there are many methods available online to get rid of this annoying pop-up asking for subscription, but the one I would prefer and also the simplest one is to just change the url and you are good to go. If you’ll look at the url you will see the structure like -

http://www.nytimes.com/2012/06/16/opinion/nocera-the-safest-bank.html?ref=opinion&gwh=6CB253207125D837FD4FF2FD82FA605E

You just need to remove the part after &(including &). For this example it would be -

http://www.nytimes.com/2012/06/16/opinion/nocera-the-safest-bank.html?ref=opinion

and you are done! With this url you wont get the subscription pop-up. Every time you see the pop-up you can see the & in the url, so don’t bother that there would be any other case. Happy reading!

1) Writing concise code using list comprehension – This should be a basic and easy to do thing for every Python user. This is also one of the Python’s thing which lets you make your code pretty concise. Example –

>>> [x*x for x in range(10)]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

2) Transposing matrices using zip function – If you want to achieve quick transpose of a matrix represented in form of lists, you can achieve it in single line using zip function. Example -

>>> matrix = [[1,2,3],[4,5,6],[7,8,9],[10,11,12]]
>>> zip(*matrix)
[(1, 4, 7, 10), (2, 5, 8, 11), (3, 6, 9, 12)]

3) Passing arguments using splat operator(*) – If a function takes 5 arguments and you have those 5 arguments in a list or dictionary, then you need not pass each element separately. Instead what you can do is, pass the whole list or dictionary to function with splat operator(*) and it will expand itself there. Example -

>>> def func(a, b, c):
    print a, b, c

>>> lst = [11, 12, 13]
>>> func(*lst)
11 12 13

4) Swapping two variables using tuples – Two(or more) variables can be swapped using tuples in a single line of code. Example -

>>> a = 10
>>> b = 5
>>> a, b = b, a
>>> a
5
>>> b
10

5)  Checking if a string is part of another string – If you want to check if a string is part of another string and doesn’t need to know any other info like its position in the string and all, then instead of looking for the substring using the find function, you can simply use in. Example -

>>> a = "my name is harsh"
>>> b = "name"
>>> if b in a:
    print "yes"

yes
>>> 

6) Using lambda functions inside list comprehensions – This is needed when you want to apply a function to all the elements of the list and hence generate a new list from those results. Example -

>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> map(lambda i,j: i*j, x, y)
[4, 10, 18]

7) Reducing the list – This is needed when you want to run a function on all the elements on the list and want one consolidated result, like sum of all elements. Example -

>>> n = [1, 2, 3, 4, 5]
>>> s = reduce(lambda x,y: x+y, n)
>>> s
15

Sum all the digits of a number in one line – This can be achieved using sum and map functions and string typecasting. Example -

>>> n = 39589
>>> sum(map(int, str(n)))
34

I’ll keep adding more to this post, once I find more tricks or if you know of any trick not listed here, you can say via a comment. So please subscribe or bookmark!

bash-3.1$ ssh -Tv git@github.com
OpenSSH_4.6p1, OpenSSL 0.9.8e 23 Feb 2007
debug1: Reading configuration data /c/Documents and Settings/hjha/.ssh/config
debug1: Applying options for github.com
debug1: Executing proxy command: exec C:/Git/bin/connect.exe -H xxxxxxxxxxxxxxxxxx
debug1: permanently_drop_suid: 500
debug1: identity file C:\\Documents\\ and\\ Settings\\hjha\\\\.ssh\\id_rsa type
-1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.1p1 Debia
n-5github2
debug1: match: OpenSSH_5.1p1 Debian-5github2 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.6
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none

debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host ‘github.com’ is known and matches the RSA host key.
debug1: Found key in /c/Documents and Settings/hjha/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: C:\\Documents\\ and\\ Settings\\hjha\\\\.ssh\\id_rsa

debug1: No more authentication methods to try.
Permission denied (publickey).
bash-3.1$ ssh git@github.com
Permission denied (publickey).

It shows up as “Permission Denied (publickey)”, to which you will find many solutions on net. But all have same underlying reason which is – ssh cannot find the location of keys because of which it shows -

debug1: Trying private key: C:\\Documents\\ and\\ Settings\\hjha\\\\.ssh\\id_rsa

Here “Trying private keys” means that ssh is trying to look for the key at the given location but could not find it. More details can be seen here under the heading “Finding out what keys ssh is using”. Now the possible reasons as you will find would be like “keys are not named properly” or “ssh doesn’t know the path to the keys” which seem to be valid reason and you can use ssh-add to add path if in your case ssh can’t find the path to keys.

But, in my case situation was totally different, ssh keys were placed at right locations but ssh was looking for keys at wrong location(or a location which literally doesn’t even exist). To make it right I just opened my config file which would be placed at ~/.ssh and looks something like -

ProxyCommand C:/Git/bin/connect.exe -H xxxxxxxxxxxxxxxxxxx

Host github.com
User git
Port 22
Hostname github.com
IdentityFile "C:\Documents\ and\ Settings\hjha\\.ssh\id_rsa"
TCPKeepAlive yes
IdentitiesOnly yes

Host ssh.github.com
User git
Port 443
Hostname ssh.github.com
IdentityFile "C:\Documents\ and\ Settings\hjha\\.ssh\id_rsa"
TCPKeepAlive yes
IdentitiesOnly yes

I saw that there were redundant backslashes placed in the IdentityFile locations. So, I edited my config file to -

ProxyCommand C:/Git/bin/connect.exe -H xxxxxxxxxxxxxxxxxxxxxxx

Host github.com
User git
Port 22
Hostname github.com
IdentityFile "C:\Documents and Settings\hjha\.ssh\id_rsa"
TCPKeepAlive yes
IdentitiesOnly yes

Host ssh.github.com
User git
Port 443
Hostname ssh.github.com
IdentityFile "C:\Documents and Settings\hjha\.ssh\id_rsa"
TCPKeepAlive yes
IdentitiesOnly yes

It simply means that if you are using double quotes to give any location then you need to give the path as it is without escaping spaces and special characters with backward slash. I tried sshing again with ssh -vT git@github.com and whoa! It worked!

x, y = y, x

“x, y” defines a new tuple which takes the values of old variables which are presented in the form of another tuple as “y, x”.