How to install Google Chrome on Ubuntu / Linux mint [via PPA]

Google Chrome, the most popular browser, is available for Linux. While Chromium, the open source version of chrome is there by default in ubuntu repository, we need to add google chrome source to the repository by ourself.

Follow the below steps to install Google Chrome in Linux mint / Ubuntu 14.04 , 16.04

How to compile and run Java program in Linux / Ubuntu Terminal

Writing a Java program is quite straight forward in Linux systems, no matter what linux distro (Linux Mint / Ubuntu / Debian / Arch Linux) you have, the steps will same except for step 1 which is installation, it may differ distro to distro

Here we will write, compile and execute a simple HelloWorld Program.

Ipython, an alternative Interactive Python interpreter [tutorial]

Ipython is an interactive python shell which can be used as a replacement for your default python interpreter.

Install Ipython

pip install Ipython

Launch Ipython

Just enter ipython in your terminal

aman@vostro:~$ ipython
Python 3.5.2 (default, Nov 23 2017, 16:37:01) 
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.

Rearrange Bootstrap Column Order with Push and Pull Classes

Suppose you have three columns, left-sidebar, main-content, right-sidebar. when the page is opened on small screen size the left-sidebar will be stacked at the top followed by the main-content and right-sidebar.

What if you wanted to get the main-content at the top followed by the left-sidebar and right-sidebar?

This can be accomplished by the bootstrap column push and pull classes.

<div class="row">

 <div class="col-sm-8 col-sm-push-2">
  <div style="background-color:red;color:#fff">main-content</div>
 </div>

 <div class="col-sm-2 col-sm-pull-8">
  <div style="background-color:blue;color:#fff">left-sidebar</div>
 </div>

 <div class="col-sm-2">
  <div style="background-color:blue;color:#fff">right-sidebar</div>
 </div>

</div>

on large display

on mobile display

Some Useful Tmux Shortcuts and Cheatsheet

Tmux is a terminal multiplexer. it's can be used to create several window panes. Create sessions and much more.
Tmux is particularly very useful on remote terminals, I like to use Vim as a text-editor with Tmux.

Open Tmux

tmux

Minify JavaScript / CSS with Django Compressor

Django Compressor minifies JavaScript and CSS files. It can combine several inline or linked files into cacheable static files. it also supports uglify wih yuglify compressor

Install Django Compressor

pip install django_compressor

In your settings.py

INSTALLED_APPS = (
    # Add compressor to the installed apps
    "compressor",
)

COMPRESS_ENABLED = True

STATICFILES_FINDERS = (
    'django.contrib.staticfiles.finders.FileSystemFinder',
    'django.contrib.staticfiles.finders.AppDirectoriesFinder',
    # other finders..
    'compressor.finders.CompressorFinder',
)

COMPRESS_ENABLED = True

#add filters
 
COMPRESS_CSS_FILTERS = [
    'compressor.filters.cssmin.CSSMinFilter'
]
COMPRESS_JS_FILTERS = [
    'compressor.filters.jsmin.JSMinFilter'
]

Usage

{% compress css %}
<link rel="stylesheet" href="/static/css/example.css" type="text/css">
<style>p { font-size:5px; color:green;}</style>
<link rel="stylesheet" href="/static/css/example2.css" type="text/css" charset="utf-8">
{% endcompress %}

{% compress js %}
<script src="/static/js/example.js"></script>
<script> console.log("some msg"); function sample() { console.log("some function definition") }</script>
{% endcompress %}

Result:

<link rel="stylesheet" href="/static/CACHE/css/07786f58by27.css" type="text/css" />
<script type="text/javascript" src="/static/CACHE/js/70850ie6975h.js"></script>

Automatically create OneToOneField in Django

The Django-annoying package contains various useful functions and AutoOneToOneField is one of them.

Using AutoOneToOneField a related object is automatically created when the parent object is created.

In this example, whenever a new user account is created, a corresponding Profile is also created

Important: The child object is not created unless it is accessed.

1. Install

pip install django-annoying

2. In your models

from django.contrib.auth.models import User
from annoying.fields import AutoOneToOneField

class Profile(models.Model):
    user = AutoOneToOneField(User, primary_key=True)
    name = models.CharField(max_length=255, blank=True)
    age = models.IntegerField(blank=True, null=True)

3. Accessing the Child Object

As I mentioned that the child object won't be created usless it is accessed.

so, in you view you might wanna do something like this.

def saveprofile(request):
    u = User.objects.get(username=request.user)
    print(u.player) #accessing child object

That's it!

3 Common ways to Reverse a String in Python

One of the very common problems in any programming language is how to reverse a String.

Let's see a few ways to do this in python.

1. Using String Slicing

well first of all the most easy way.. Here we are using the power of String Slicing. Just a single line command!

-1 at the last index means reading from end. and the first two empty index means that we are considering the whole string. 

mystring = "Hello World"
rev = mystring[::-1]
print(rev)

How to Install SQLite3 in Ubuntu / Linux Mint

SQlite is an Embedded Relational Database Management System. SQlite does not require a server to run unlike mysql or other popular dbms.


To install Sqlite3 in Ubuntu / Linux Mint issue the following commands

This will work for Ubuntu 14.04 and above

sudo apt-get update
sudo apt-get install sqlite3 libsqlite3-dev

Install TypeScript Syntax highlighting in Sublime Text Editor

We will need the TypeScript Package to get Syntax highlighting to work. we will install the package using Package Control.

So, first go ahead and install Package Control

Now, go to preferences, where you can now find Package Control option, click on it .

Python Program to Check if a number is FIbonacci

In Fibonacci Sequence, every previous two numbers gives the next number.

the first 10 Fibonacci numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 35


In this python Program we will see how to test if a number given by user belongs to the Fibonacci sequence.

If the given number is n then any of 5n*n + 4 or 5n*n - 4 or both should be a perfect square to be a Fibonacci number.

Python Code:

import math

def CheckPerfect(x):
  i = int(math.sqrt(x))
  return (x == i*i)

def CheckFibo(n):
  if(CheckPerfect(5*n*n + 4) or CheckPerfect(5*n*n - 4)):
    print("Fibonacci")
  else:
    print("Not Fibonacci")

CheckFibo(89) #this returns true, 89 is Fibonacci

you can suggest better algorithm for this in the comments!

Python Program to check if a number is Perfect Square

A number that can be expressed as the product of two equal integers is a Perfect Square number.

for example: 25 can be expressed as 5 x 5

In the given python3 code we take a user input and take out the square root and convert it into integer. if square root value multiplied by itself equals the user given number then its proved to be a Perfect number else not. 

import math

n = int(input())

i = int(math.sqrt(n)) #sqrt function returns float so typecasting to int

if(n == i*i):
  print("perfect Square: %d * %d = %d"%(i,i,n))
else:
  print("Not Perfect Square")

Please comment below if you have a better algorithm than the given one.

How to Fix - Operational Error: cannot open database in Django Sqlite3

This may be a permission problem.

the database file must be writable to the user

you need to grant permission to db.sqlite3

here, myproject is the folder which contains db.sqlite3 file

chmod 664 /path/to/myproject/db.sqlite3
sudo chown :www-data /path/to/myproject/db.sqlite3 
sudo chown :www-data /path/to/myproject

also give necessary permissions to the folder that contains the sqlite3 database file. the database engine should be able to write a lockfile to the parent directory of the database file.

sudo chmod 775 /path/to/myproject

Get Free SSL certificate with Let's Encrypt on Ubuntu Apache Server

Let's Encrypt is an open certificate authority and provides free SSL Certificates. It's popular for it's simplicity to setup. It's been founded by Mozilla, Cisco and many more.

The setup process is very simple, I have explained it in 3 steps:
In the bottom section I have also mentioned the problems I faced and the solutions that worked.


Make Sure that your website is running on Apache server configured through VirtualHosts and specifies ServerName

How to link a custom domain name to AWS EC2 instance

if you have created your Amazon AWS EC2 instance, you can now access it on the web using your given public ip or public DNS (something like ec2-54-36-73-206.us-west-2.compute.amazonaws.com), you can find these in the description of the instance.

But you need to access your website just using you own domain like example.com

Here are the steps to do so very easily: