Python Class Attributes: An Overly Thorough Guide

This article is originally published at Toptal.

I had a programming interview recently, a phone-screen in which we used a collaborative text editor.

I was asked to implement a certain API, and chose to do so in Python. Abstracting away the problem statement, let’s say I needed a class whose instances stored some 

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      data
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</tr>

 and some 

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      other_data
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.

Rails Service Objects: A Comprehensive Guide

This post was written by Amin Shah Gilani, Ruby Developer for Toptal.

Ruby on Rails ships with everything you need to prototype your application quickly, but when your codebase starts growing, you’ll run into scenarios where the conventional Fat Model, Skinny Controller mantra breaks. When your business logic can’t fit into either a model or a controller, that’s when service objects come in and let us separate every business action into its own Ruby object.

Display IP address in console login screen

Here is one liner that will add the current IP address in the console login screen (if you are not running X as is case for servers):

(ip -o -4 a| awk '$2 !="lo" {print "\nIP Address ::"$4}' |tr '\n' ',';echo)>>/etc/issue

Just execute the above command as root. It will add the required code in “/etc/issue” to display the IP address. BTW, you can also use “\4” or “\6” instead of that command to get the IP but that will not work with some old versions of Linux.

Port php mysql scripts to php 7.0 from 5.x version

Recently I got a script or series of scripts that were written for PHP 5.6x and hence used mysql_connect which as you know by now does not work with PHP 7.0. Since there were number of scripts, I thought it would be waste of time to change them manually and wrote a script to fix them. If you have similar situation then probably this few lines could help you.

Since my scripts did not use all the functions so I did not put the sed commands for all of them but you get the idea 🙂

Linked clone with qemu-img

As you would have seen in Virtualbox or vmware, there is option to create a linked clone. I wanted to use the same feature as “Snapshot” feature anyway does not look/work so great with virt-manager. So, I created a script to create a linked clone VM and here it is :

#!/bin/bash - 
#===============================================================================
#
#          FILE: qcow2-linked-clone.sh
# 
#         USAGE: ./qcow2-linked-clone.sh 
# 
#   DESCRIPTION: 
# 
#       OPTIONS: ---
#  REQUIREMENTS: ---
#          BUGS: ---
#         NOTES: ---
#        AUTHOR: Amit Agarwal (aka)
#  ORGANIZATION: Mobileum
#       CREATED: 01/05/2018 09:54
# Last modified: Wed Feb 28, 2018  04:39PM
#      REVISION:  ---
#===============================================================================

set -o nounset                              # Treat unset variables as an error
UP="amitag:amitag" #Here you need to put your username and group.

if [[ $# == 0 ]]
then
    read -p "Enter the source path :: " spath
    read -p "Enter the source disk :: " sdisk
    read -p "Enter the destin path :: " dpath
    read -p "Enter the destin disk :: " ddisk
    read -p "Enter new VMName :: " vmname
else
    spath=$(dirname $1)
    dpath=$spath
    sdisk=$(basename $1)
    ddisk=$2.qcow2
    vmname=$2
fi


sudo chown $UP "$spath/$sdisk"
qemu-img create -f qcow2 -b "$spath/$sdisk" "$dpath/$ddisk"

virt-install --disk $dpath/$ddisk --ram 512 \
    --virt-type kvm --vcpus 1 --name "$vmname" --import

The script will create a linked qcow2 and then create a VM with that image. Running it is simple, either provide command line options or just run and it will ask you for details.

Monitor progress of coreutils commad like mv, cp etc

Monitor progress of coreutils commad like mv, cp etc

You can use command called “progress”. Other option is “pv” but that is little complicated so here is simpler option.

Progress – A Tiny Tool to Monitor Progress for (cp, mv, dd, tar, etc.) Commands in Linux

To install, you can do the following:

dnf install progress

vagrant box to libvirtd (QEMU) VM

Like ova images, you can use box images as well with Qemu. After all, both have the disk images, so here is the script to do that. Just put the script somewhere in your path and run with ova or box image name :

#!/bin/bash - 
#===============================================================================
#
#          FILE: ova2vm.sh
# 
#         USAGE: ./ova2vm.sh 
# 
#   DESCRIPTION: 
# 
#       OPTIONS: ---
#  REQUIREMENTS: ---
#          BUGS: ---
#         NOTES: ---
#        AUTHOR: Amit Agarwal (aka),
#  ORGANIZATION: Mobileum
#       CREATED: 12/28/2017 13:59
# Last modified: Sun Mar 11, 2018  12:01PM
#      REVISION:  ---
#===============================================================================

set -o nounset                              # Treat unset variables as an error
dest='/mnt/Backup/VM'
ORIG=${PWD}

if [[ $# == 0 ]]
then
    echo "You need to provide ova/vmdk filename"
    exit
fi
if [[ $1 == *ova || $1 == *box ]]
then
    tmp=$(mktemp -d /tmp/amitXXXXXXX)
    cd  $tmp
    tar xvf $ORIG/$1
    file=$(echo $PWD/*vmdk)
else
    file=$1
    echo "Not a OVA file"
fi
dfile="$dest/$(basename $file)"

read -p "Enter the name for VM :: " vmname
qemu-img convert $file $dfile -p -c -O qcow2
virt-install --disk $dfile --ram 512 \
    --virt-type kvm --vcpus 1 --name "$vmname" --import