### Writing a calculator using stacks in Python

I wrote a calculator in Python. Again. But this time, I didn't write the UI layer. Because principles! Here at Enthought, it's advised to have a clear seperation between the Model and the View and what you see below is the Model part of the calculator. It also makes life easier in two ways. First, it makes testing the underlying model and it's methods easier. Secondly, I can implement the UI however I want to, i.e using traitsUI, raw Qt, Jigna. Whatever!

If you don't understand what's going on in the code, let me explain things a little. There is a standard Python list called inputstack, and it uses as a stack, that stores all of the input characters, let them be numbers or an operator. And the eval_stack method will traverse the inputstack checking for numbers or operators.

Also, this Github repository contains all the calculator codes I've written so far! Again, as always, the code was highlighted and embedded into this blogpost as raw html using hilite.me! Try it! It's awesome!

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 import unittest class Application(): inputstack = [] def eval_stack(self): i = 0 # counter to keep track of decimal point temp = 0 # counter to keep track of current input temp2 = 0 # counter to store previous input op = '' # used to store the math operator while self.inputstack != []: if not isinstance(self.inputstack[-1], basestring): temp += int(self.inputstack.pop())*10**i i += 1 print temp else : if self.inputstack[-1] == '.': self.inputstack.pop() temp = temp/(10.**(i)) i = 0 print temp else : op = self.inputstack.pop() temp2 = temp temp = 0 i = 0 print op, temp, temp2 if op == '+': return temp2 + temp elif op == '-': return temp - temp2 elif op == '*': return temp*temp2 elif op == '/': return float(temp)/temp2 class testApplication(unittest.TestCase): def test_add(self): test = Application() test.inputstack = [1,2,'+',3,4] self.assertEqual(test.eval_stack(), 46) def test_add_float(self): test = Application() test.inputstack = [1,2,'.',4,'+',3,4,'.',5] self.assertEqual(test.eval_stack(), 46.9) def test_sub(self): test = Application() test.inputstack = [1,2,'-',3,4] self.assertEqual(test.eval_stack(), -22) def test_sub_float(self): test = Application() test.inputstack = [1,2,'.',4,'-',3,4,'.',5] self.assertEqual(test.eval_stack(), -22.1) def test_mul(self): test = Application() test.inputstack = [1,2,'*',4] self.assertEqual(test.eval_stack(), 48) def test_mul_float(self): test = Application() test.inputstack = [1,'.',4,'*',3,'.',5] self.assertEqual(test.eval_stack(), 4.9) def test_div(self): test = Application() test.inputstack = [1,2,'/',4] self.assertEqual(test.eval_stack(), 3.0) def test_div_float(self): test = Application() test.inputstack = [1,'/',5] self.assertEqual(test.eval_stack(), 0.2) 

### Animation using GNUPlot

Animation using GNUPlotI've been trying to create an animation depicting a quasar spectrum moving across the 5 SDSS pass bands with respect to redshift. It is important to visualise what emission lines are moving in and out of bands to be able to understand the color-redshift plots and the changes in it.
I've tried doing this using the animate function in matplotlib, python but i wasn't able to make it work - meaning i worked on it for a couple of days and then i gave up, not having found solutions for my problems on the internet.
And then i came across this site, where the gunn-peterson trough and the lyman alpha forest have been depicted - in a beautiful manner. And this got me interested in using js and d3 to do the animations and make it dynamic - using sliders etc.
In the meanwhile, i thought i'd look up and see if there was a way to create animations in gnuplot and whoopdedoo, what do i find but nirvana!

In the image, you see 5 static curves and one dynam…

### on MOOCs.

For those of you who don't know, MOOC stands for Massively Open Online Course.

The internet is an awesome thing. It's making education free for all. Well, mostly free. But it's surprising at the width and depth of courses being offered online. And it looks like they are also having an impact on students, especially those from universities that are not top ranked. Students in all parts of the world can now get a first class education experience, thanks to courses offered by Stanford, MIT, Caltech, etc.

I'm talking about MOOCs because one of my new year resolutions is to take online courses, atleast 2 per semester (6 months). And I've chosen the following two courses on edX - Analyzing Big Data with Microsoft R Server and Data Science Essentials for now. I looked at courses on Coursera but I couldn't find any which was worthy and free. There are a lot more MOOC providers out there but let's start here. And I feel like the two courses are relevant to where I …

### On programmers.

I just watched this brilliant keynote today. It's a commentary on Programmers and the software development industry/ecosystem as a whole.

I am not going to give you a tl;dr version of the talk because it is a talk that I believe everyone should watch, that everyone should learn from. Instead, I am going to give my own parallel-ish views on programmers and programming.
As pointed out in the talk, there are mythical creatures in the software development industry who are revered as gods. Guido Van Rossum, the creator of Python, was given the title Benevolent Dictator For Life (BDFL). People flock around the creators of popular languages or libraries. They are god-like to most programmers and are treated like gods. By which, I mean to say, we assume they don't have flaws. That they are infallible. That they are perfect.
And alongside this belief in the infallibility of these Gods, we believe that they were born programmers. That programming is something that people are born wit…