Debugging a crucial skill but very rarely taught

Listening on software engineering radio podcast Diomidis Spinellis mentions how debugging is so much important in software development but still, we don’t teach much in-depth this skill in our universities. I and believe any other programmer will agree that debugging tools are the key arsenal in fixing bugs and even understanding the system.

Either you use modern tools or just by basic print/printf statements that don’t matter. Students should learn these key skills and professors should emphasize on educating and not only in universities even in industry set-up when a new developer joins in there should be good exposure to debugging so that they dissect code base and become productive fast.

Worth considering I think …

What do you think? Please share in comments.

Date print formats Perl Date::Manip

Perl Date::Manip is one of the modules which I use a lot. It’s a wonderful lib and has very clean API with great documentation. Below is a quick look at Date::Manip print format options which sometimes is very handy. For detailed interpretation and other options encourage to go through Date::Manip on CPAN

Example:

my $present_date_hash = Date::Manip::Date->new("today");
my $present_date = $present_date_hash->printf("%Y-%m-%d %H:%M:%S");

Happy Coding!

also, can check my previous article on generating date patterns using Date::Manip

Algorithms performance: big O notation: simplified short notes

 The big O notation is used to analyze runtime time complexity. big O notation provides an abstract measurement by which we can judge the performance of algorithms without using mathematical proofs. Some of the most common big O notations are:

  • O(1) : constant: the operation doesn’t depend on the size of its input, e.g. adding a node to the tail of a linked list where we always maintain a pointer to the tail node.
  • O(n): linear: the run time complexity is proportionate to the size of n.
  • O(log n): logarithmic: normally associated with algorithms that break the problem into similar chunks per each invocation, e.g. searching a binary search tree.
  • O(n log n): just n log n: usually associated with an algorithm that breaks the problem into smaller chunks per each invocation, and then takes the results of these smaller chunks and stitches them back together, e.g, quicksort.
  • O(n2): quadratic: e.g. bubble sort.
  • O(n3): cubic: very rare
  • O(2n): exponential: incredibly rare.

Brief explanation:     
Cubic and exponential algorithms should only ever be used for very small problems (if ever!); avoid them if feasibly possible. If you encounter them then this is really a signal for you to review the design of your algorithm always look for algorithm optimization particularly loops and recursive calls. 

The biggest asset that big O notation gives us is that it allows us to essentially discard things like hardware means if you have two sorting algorithms, one with a quadric run time and the other with a logarithmic run time then logarithmic algorithm will always be faster than the quadratic one when the data set becomes suitably large. This applies even if the former is ran on a machine that is far faster than the latter, Why?

Because big O notation isolates a key factor in algorithm analysis: growth. An algorithm with quadratic run time grows faster than one with logarithmic run time.

Note: The above notes are for quick reference. Understanding algorithmic performance is a complex but interesting field. I would recommend picking a good book to understand the nitty-gritty of big O and other notations.

Python learning: scrapbook

While browsing my Evernote I found a scrapbook which I have made while learning Python some years back. Thought to share if this helps someone. I am pasting directly (no editing so there might be some spell and grammar mistake).

  • Python 2 division, just use integer part (3/2=1) whereas Python 3 uses real division 3/2 = 1.5
  • Strings in Python are immutable means you can’t change the in-place value of a char. Once string is created you can’t change/replace its elements
  •  s= “Hello World” s[::-1] this will reverse string s “dlroW olleH” double colon is used to tell the range and also how many elements can be skipped
  • if you want to use Python 3 functions in Python 2 then use ‘from __future__ import print_function‘ and similarly other functions 
  • List are mutable but tuples are not mutable (does not support item assignment) aka immutable, fewer methods in tuples then why to use instead of a list? The key is immutability. in a program if you want sequence/Val does not to get changed then tuple is a solution e.g.; storing calendar dates which know will not change during your programs. 
  • Set is a collection of un-ordered unique items it looks like a dictionary (in notation) but only keys which are unique. It can help in removing repeated items means you can use set to cast list.
  • List comprehensive are an excellent way to write clean and efficient code – they are actually de-constructed for loop flatted out in a list
  • Lambda expressions can be used to shorten function this is really useful when used with map(), reduce() and filter() functions
  • First class functions: Treat functions like any other object, we can pass functions, we can return functions, we can assign functions to a variable
  • Closure: Closure takes advantage of first-class functions and returns inner functions and variables local to them.
  • Decorators: It is a function which takes another function as an argument and returns as a function without changing the source code of the original function. Decorator allows easily to add functionality inside our wrapper without modifying original function. 

Note: These are notes for quick reference. If you are serious in learning Python I encourage you to take a book or a tutorial.

Enjoy learning! More to come …

Perl development journey and books collection

While doing routine cleaning of my personal library I was surprised to see the Perl book collection I have made over the period of time. My Perl dev journey started in a full-fledged manner way back in fall 2007. Prior to that was mainly developing using C, C++, assembly language. My first impression with Perl was not very exciting mainly due to ugly syntax and the way the OO is achieved and being from C++ background initially it was really difficult to grasp. But over the years working with language and while developing a large scale web application I learned a lot of nitty-gritty of the language and still learning…  Today I can vouch for Perl for its speed, portability, great module system CPAN and excellent dedicated community. Thanks to all the module authors and contributors on Perl Monks and StackOverflow. You guys are amazing! 
Now, the books which helped me immensely to wrote better Perl programs.

New coder and Experienced coders

I’ve found that a big difference between new coders and experienced coders is faith: faith that things are going wrong for a logical and discoverable reason, faith that problems are fixable, faith that there is a way to accomplish the goal. The path from “not working” to “working” might not be obvious, but with patience, you can usually find it.

Read the above quote somewhere on medium, myself as a programmer can easily sync with the saying. Have observed this many many times in my coding experience of the last two decades. To add, patience is needed much more while dealing with critical real-time production bugs.

I personally feel that analysis of the problem with a cool head and focus and pateince is is the key to debug and resolve critical problems.

Happy Coding!

date sorting in datatables using moment js

Sorting dates could be tricky because of various date and time format used. Fortunately there is awsome js lib called moment.js library avaliable, this is free and open source. I have made a small demo of how moment.js is used with datatables. for date sorting. First let have a look into how many date time types which moment.js supports.

Format Dates

moment().format('MMMM Do YYYY, h:mm:ss a'); // March 12th 2019, 6:46:42 pm
moment().format('dddd');                    // Tuesday
moment().format("MMM Do YY");               // Mar 12th 19
moment().format('YYYY [escaped] YYYY');     // 2019 escaped 2019
moment().format();                          // 2019-03-12T18:46:42+05:30
                                            // undefined

Relative Time

moment("20111031", "YYYYMMDD").fromNow(); // 7 years ago
moment("20120620", "YYYYMMDD").fromNow(); // 7 years ago
moment().startOf('day').fromNow();        // 19 hours ago
moment().endOf('day').fromNow();          // in 5 hours
moment().startOf('hour').fromNow();       // an hour ago
                                          // undefined

Calendar Time

moment().subtract(10, 'days').calendar(); // 03/02/2019
moment().subtract(6, 'days').calendar();  // Last Wednesday at 6:46 PM
moment().subtract(3, 'days').calendar();  // Last Saturday at 6:46 PM
moment().subtract(1, 'days').calendar();  // Yesterday at 6:46 PM
moment().calendar();                      // Today at 6:46 PM
moment().add(1, 'days').calendar();       // Tomorrow at 6:46 PM
moment().add(3, 'days').calendar();       // Friday at 6:46 PM
moment().add(10, 'days').calendar();      // 03/22/2019
                                          // undefined

Multiple Locale Support

moment.locale();         // en
moment().format('LT');   // 6:46 PM
moment().format('LTS');  // 6:46:42 PM
moment().format('L');    // 03/12/2019
moment().format('l');    // 3/12/2019
moment().format('LL');   // March 12, 2019
moment().format('ll');   // Mar 12, 2019
moment().format('LLL');  // March 12, 2019 6:46 PM
moment().format('lll');  // Mar 12, 2019 6:46 PM
moment().format('LLLL'); // Tuesday, March 12, 2019 6:46 PM
moment().format('llll'); // Tue, Mar 12, 2019 6:46 PM
                        

I have used the following libs to make this demo:

  • jquery
  • data table
  • moment.js
  • datetime-moment.js

HTML source


<h3 class="ui_title">Employee joining data</h3>
<div class="ui_block">
<table id="myTable1" class="ui_table">
<thead id="table_head">
<tr>
<th style="width:150px;">Name</th>
<th style="width:50px;">Designation</th>
<th>Joining date</th>
</tr>
</thead>
<tbody>
<tr>
	<td>Ram</td>	
	<td>Engineer</td>
	<td>18/10/2015</td>	
</tr>
<tr>
	<td>Shyam</td>	
	<td>Engineer</td>
	<td>05/01/2012</td>	
</tr>
<tr>
	<td>Suresh</td>	
	<td>Sr. Engineer</td>
	<td>22/06/2010</td>	
</tr>
<tr>
	<td>Ahmed</td>	
	<td>Manager</td>
	<td>02/02/2002</td>	
</tr>
<tr>
	<td>Leena</td>	
	<td>Sr. Manager</td>
	<td>01/01/2018</td>	
</tr>
<tr>
	<td>Pradeep</td>	
	<td>Architect</td>
	<td>21/05/2012</td>	
</tr>
</tbody>
</table>
</div>

jQuery

jQuery(document).ready(function() {
$.fn.dataTableExt.oPagination.iFullNumbersShowPages = 3;
$.fn.dataTable.moment('DD/MM/YYYY');
		$("#myTable1").DataTable({	
		"autoWidth": false,
		"destroy": true,
		"order": [[2, 'desc']],
		"pageLength": 15,
		"lengthMenu": [ [10, 25, 50, -1], [10, 25, 50, "All"] ],
		"pagingType": "full_numbers"
});
});	

CSS

/* 1. GENERAL */
* {
	font-family: /* 'Roboto', */ Verdana, Arial, Helvetica, sans-serif;
	font-size: 13px;
	box-sizing: border-box;
}

body {
	font-family: /* 'Roboto', */ Verdana, Arial, sans-serif;
	background: #f8f8f8; /* e2dbc5; */
	margin: 1em;
}

.ui_title {
	font-family: /* 'Open Sans', */ Verdana, sans-serif;
	color: #2A3F54;
	font-weight: 400;
	font-size: 24px;
	line-height:26.4px;
	border-bottom: 1px solid  #2A3F54;
}

.ui_title i {
	font-size: 24px;
}

/* BLOCKS */
.ui_block {
	min-width: 20px;
	background: white;
	border: 0; /* 1px solid #ebebeb;*/
	padding: 1em 1em;
	margin-bottom: 2em;
	box-shadow: 0 4px 6px 0 hsla(0,0%,0%,0.2);
}

.ui_block h3,
.ui_block h3 i {
	font-family: /* 'Open Sans', */ Verdana, sans-serif;
	border-bottom: 2px solid rgb(230,233,237);
	color: rgb(115,135,156);
	font-weight: 400;
	font-size: 16px;
	line-height: 18.7px;
	padding: 0;
	margin: 1em 0 0.5em 0;
}
.ui_block h3:first-child {
	margin: 0.5em 0 0.5em 0;
}

/* 3. TABLE */
.ui_table {
	border: 1px solid black;
	border-collapse: collapse;
	width:100%;
	margin-bottom: 1em;
}
.ui_table th {
	text-align: left;
	background: lightgray;
}
.ui_table td,
.ui_table th {
	border: 1px solid gray;
	padding: 3px 5px;
	font-size: 10pt;
	font-weight: 400;
}

Demo

jsFiddle
https://jsfiddle.net/ppant/efL3pvq2/3/
Github
https://github.com/ppant/jshacks/blob/master/data-table-date-sorting.html

References:


git amend scenerios

Sometimes we need to change the commit message of already committed/committed-pushed files. See below some of the scenarios might arise..

Scenerio 1-> Committed but not pushed

$ git commit --amend

This will open an editor with the commit message. If you are using vi editor edit the commit message and save using !wq: Check with $git log if the message has been amended correctly.

Scenerio 2-> Already pushed + most recent commit

It might be the case that if a user has already pushed the changes to git central repository, in this type of scenario we need to first amend the most recent local commit and afterward apply –force push which will forcefully push the changes to the server. In this process, one thing to keep in mind is that if in between any other user who has already synced local copy with the central repository needs to re-pull.

 $ git commit --amend
Edit the message in vi and save and exit
$ git push origin <branch_name> --force


Scenerio 3-> Not pushed + old commit

$ git rebase -i HEAD~X

where X is the number of commits to go back then move to the line of your commit, change pick and edit then change your commit message

$ git commit --amend 

Finish the rebase with:

$ git rebase --continue

Rebase opened your history and let you pick what to change. With edit, you tell that you want to change the message. Git moves you to a new branch to let you –amend the message. git rebase — continue puts you back in your previous branch with the message changes.

alternatively, you can choose reword instead of edit when rebasing to change the commit directly. Then you can skip the amend and rebase continue. You may check this link from git book for more on this.

Scenerio 4-> Already pushed + old commit
Edit your message with the same 3 steps process as menined in scenerios 2 ( rebase –i, commit –amend, rebase –continue). Then force push the commit

$git push <branch_name> master --force

But! please remember re-pushing your commit after changing it will very likely to prevent others to sync with the repo, if they already pulled a copy. You should first check with them.


References:
https://gist.github.com/nepsilon/156387acf9e1e72d48fa35c4fabef0b4

https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History


SpaceVim review

As a Vim user for nearly 2 decades, recently I got an opportunity to explore
SpaceVim a new Vim distribution. Some of the features worth highlighting are:

  • Nicely built edit mode.
  • Loved the idea of collecting related plugins together to provide features.
  • Instant search results using grep, ag, rgackpt and with a great UI.

Will exlore more features in coming days and shall update the post.

Gitbub:https://github.com/SpaceVim/SpaceVim