### 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…