Saturday, December 10, 2011

Unplanned cycle ride and Python

Around May 2011, the time I decided to go on solo bike rides and GoogleMaps has been of great help ever since. It was only after a few months, I realized there was a python binding for GoogleMaps. Only after going on an unplanned solo cycling trip recently, I realized how much of a help it can be. Since most of the times I'm on highways and well raid roads, it is possible to get the elevation of the whole route. When the elevations are plotted, it gives a vague idea of the terrain. On the left the terrain of road from Channarayapatna to Hassan (Elevation is in mtrs).

Enough talk and here is the code. The elevation api has been used to get elevation of a point and googlemaps api has been used to get the latitude and longitude of start and end points. The points along the route have been interpolated as of now. But they can be obtained point by point using googlemaps api and interpolated based on the distance.

Will probably do all that and make another post soon. Happy coding till then.

Tuesday, September 6, 2011

Enumerating Palindromic Numbers

A palindromic number remains same when reversed. Ex: 141, 5, 22, 1991, 27472 and so on..

I came across a problem which needed me to check if a number is a palindrome which I can do by reversing the number and comparing it with the original.

But what if I wanted all the possible palindromic numbers of a given width.

If I wanted all the 5 palindromic numbers, I can solve them by considering the number as abcba where a, b, c are digits and a!=0. The number would be a(10000) + b(1000) + c(100) + b(10) + a.

Then the problem becomes trivial.

for a in range(9, 0, -1):
for b in range(9, -1, -1):
for c in range(9, -1, -1):
num = 10001 * a + 1010 * b + 100 * c

But as we can see, it is not generic and making it generic this way, would require me to use iterators.

On a sunday morning, travelling from Krishnagiri to Dharmapuri in a local bus, at 04:14, this sweet and simple approach occured to me.

It is a recursive approach that considers the fact that all n digit palindromes can be generated by adding a digit at the front and back of the (n - 2) digit palindromes and (n - 4) digit palindromes and so on.

Ex: 5 digit palindromes are of the form
a***a where a != 0 and *** is a 3d palindrome
a0*0a where * is a 1d palindrome.

def nDigitPalins(n):

if n == 1:
return range(9, 0, -1)
elif n == 2:
return [11 * x for x in range(9, 0, -1)]
p_zeros = [i * (10 ** (n -1) + 1) for i in range(9, 0, -1)]

p = []
for base in p_zeros:
for y in range(1, (n + 1) / 2):
for subPalin in nDigitPalins(n - 2 * y):
p_num = base + subPalin * (10 ** y)

return p

print nDigitPalins(8)

You can run the code at

Wednesday, May 11, 2011

is perfect square

How do you write a program that checks if a number is perfect square or not.

def isPerfectSquare(x):
i = 0
while i * i < x:
i += 1
return i * i == x

This is such a beautiful code.

Is it??? How about this.

def isPerfectSquare(x):
xRoot = int(x ** 0.5 + 0.1)
return xRoot * xRoot == x

or in my favourite lambda way,

isPerfectSquare = lambda x: int(x ** 0.5 + 0.1) ** 2 == x

If you know what is going on, you'll love the recipe. If you don't then start thinking.

Friday, July 30, 2010

Python in Vim

What if your favorite editor can interpret your favorite language!!! That would make writing code a piece of cake. This is what happened to me recently. I knew Vim could interpret Python. Only after I tried it out, I found how easy it is.

Simply go to normal mode and do :py print 'Vim Roxx' to see what I am trying to tell. You have to include a :py at the start of the line and it runs in Vim just as if it were running on a Python interpreter.

I know how you are feeling. I felt the same way too. Isn't there a way to specify start of python code and end. There is one.
:py << EOF
print "This is cool"
print "I'm lovin it"

does the job for you. The EOF here is only a name and any variable_name can be used. You can also specify a file to execute by using :pyfile file_name

Here is a quick snippet. I would like to run the Python code from my current buffer. I want to go over a line and press f4 and expect Vim to execute that command by adding a ":py" in the start.

Hence I first do
:py << EOF
import vim
def run_line():
cmd = ":py " + vim.curent.line
So now every time I go over a line and type :py run_line() in the normal mode, the current line is run as a line of python code. All I now have to do is bind this function to the required key and nmap <f4> :py run_line() <CR> does the job for me.

Happy Vimming with Python :) :)

Thursday, July 22, 2010

Adding Polynomials

Imagine a polynomial like 2x3 - 3x2 + 5 was represented as a list of coefficients in a list like [1, -3, 0, 5]

My goal is to write a function that takes two lists and does polynomial addition on them. Ex: poly_add( [1, -2, 0, 3, 5] , [3, -1, 2] ) should return [1, -2, 3, 2, 7]

After a little brainstorming, I got this cute idea, which I felt was so cute that I should blog about it. Moreover it has been a while since I have written something.

Here is the function

def poly_add( x, y):
min_len = min( len(x), len(y))
return x[: -min_len] + y[: -min_len] + [ x[i] + y[i] for i in range(-min_len,0) ]

If this is trivial then great. If it is not so trivial, you will love the beauty behind this function and hence python itself.

I use Python and I am loving it :) :) :)

Friday, February 19, 2010

My daily routine ( monitor )

Here is how I spend my typical day
  1. wake up early in the afternoon at 11:30
  2. go online and check mail for 20 min
  3. get ready for lunch by 13:00
  4. go to the lab and spend time with my lappy till 20:00
  5. dinner
  6. again spend time in front of lappy
  7. go to bed
Looks like I spend most of the time in front of my lappy. Wonder what I do and for how long!!!
What if we had a program that monitors for how much time do we spend looking at each window on our machine. Actually why don't we write one. This brilliant idea was not mine but my friend Puneeth's. We tried to write this program long back ( on the night of 1st day, PyCon India ). But python Xlib documentation sucks. Atleast that is what I felt when I tried to refer it. Anyways luckily that night punch got quite close to finishing this program. Dunno if he finished it later on. But I wanted to try it out. I actually saw this documentation long before we started coding for this program. I wanted to have an option on right click menu to close the current window. I found something called NACT for adding options to right click on nautilus and a program called xclose that closes window using window display name. I could get xclose running and NACT configured but forgot about it later on.

Now I start googling. I found this link that got me started.Punch figured out that there is something called display and then screen and then window. Luckily I remembered those words. The blog post also talks about the same. I tried my hands on Xlib using ipython and found out what all this window thingy is all about.

Here is a small intro to Xlib that must get you started.

from Xlib.display import Display

# initialize the display
disp = Display()

# list no of screens available
disp.screen_count() # only one in my case.. my laptop screen..
# get the screen to work on
screen = disp.screen() # disp.screen(0) also works

## everything we see is a hierarchy of windows

root_window = screen.root
# this window object will have its parent equal to zero

print root_window.get_wm_name() ## the obvious

root_tree = root_window.query_tree()
root_tree.children ## gives you a list of window objects, its children
root_tree.parent ## lets you access its parent

Now I could not achieve what I exactly wanted. Figuring out what we concentrate on, looking at the cascade of windows and their sizes involves AI. All I wanted was the window that had focus and for how long. There is a method called event notify that notifies a focus change event but It involves a lot more digging into Xlib documentation and some patience to try out all that on ipython. For now, all I am going with the brute force method, polling the Xserver every n seconds. I ran the script while I was writing the blog post and here are the results.
02/19/10-16:10:58 -> ans@ans-laptop: ~/Desktop/xlib
02/19/10-16:11:08 -> Google Docs�-�Upload a File - Vimperator
02/19/10-16:11:18 -> Google Docs - All items - Vimperator
02/19/10-16:11:28 -> - Google Docs - Vimperator
02/19/10-16:11:38 -> - Google Docs - Vimperator
02/19/10-16:11:48 -> - Google Docs - Vimperator
02/19/10-16:11:58 -> Blogger: me, myself and py - Create Post - Google Chrome
02/19/10-16:12:08 -> Blogger: me, myself and py - Create Post - Google Chrome
02/19/10-16:12:18 -> Blogger: me, myself and py - Create Post - Google Chrome
02/19/10-16:12:28 -> Blogger: me, myself and py - Create Post - Google Chrome
02/19/10-16:12:38 -> Blogger: me, myself and py - Create Post - Google Chrome

I find them pretty satisfactory. Here is the code in case some one wants to hav a luk.
Happy Coding :)

Wednesday, February 17, 2010

File browser using Python

I always wanted to have a file browser ( like nautilus ) on my shell. Something like the image on the left.
I prefer to have my hands on the keyboard than shifting between keyboard and the tailed buddy.
I saw my friend Lee use something called Midnight Commander. I googled and found other alternatives here. But only MC was appealing to me. I started using it and it is a decent one. But I was not satisfied with its display. It shows all the files with in one big column and displays all the details as if some had typed "ls -l". And recently after switching to vi mode, I am finding it hard to access the arrow keys and would prefer something similar to vi. One way of achieving it is actually remapping keys in MC. But still the concept of moving left and right does not have a meaning in MC context. Moreover, we are used to things that behave like nautilus. I wanted a file browser that displays folders and files like nautilus and makes it possible to navigate using hjkl keys. I also wanted a mechanism where I could tag files just like in delicious. I finally decided I want a new file browser and I am going to write it :) .

My obvious and only choice is python. Although there is bash scripting with zenity to make your life easy, I went for python for the obvious reason. I also want the fun of coding in python. I also wanted to try out coding in python on my newly configured Vim. My idea of programming on terminals was limited to printing something on terminal. I tried out something like that long back using strings. But it was a very naive way of doing things and I didn't like it. One day I tried out something called bpython. It is another command line interpreter for python. I was fascinated by the way the program works. It is simply amazing and behaves like a proper GUI IDE on shell. Luckily my friend Madhu told me that this is written using ncurses. The word curses caught me. I thought may be it can help me out in writing my file browser. But I didnt give it much thought. I actually tried out some stuff only to see that it requires special way of approach.

So now here I am, decided to write a file browser and know a word ncurses. Where do I start... obvious google. I found a few links on ncurses and learnt that it also has a wrapper in python called "curses". But then I realised this is exactly what I did when I tried ncurses for the first time and got no where. I looked back and found out that the reason I stopped is because the moment you try to manipulate your terminal, the default behaviour of your python interpreter is lost and it gets really annoying to proceed. All you can do is write code in a file and run it every time. I wondered how would bpython behave!!. I tried basic importing and initialising screen and to my delight, it did not have any effect on bpython console. bpython being written using curses, overwrites all my actions. My interpreter is working fine. So this also has a disadvantage. Although you can see all the attributes available for any object since bpython displays attributes after you type a dot, you cant really see any change that you make. Anyways I still will have to stick to my old way of doing, writing in a file and executing.

I found a few links on how to program in curses using python.
These links got me started and python curses man page helped me through the process.

And that is how I end up with something that suits perfectly to my requirements.
Currently this is the key mapping on my PyBrowser that opens with files in current directory.
  • h - move left
  • j - move down
  • k - move up
  • l - move right
  • b - back one directory
  • o - open the directory or file( programs are mapped to filenames in a different conf file )
  • H - Toggle hidden files
  • q - close or quit
All this in 200 lines of code and 2 days of work with loooots of breaks. Now you know why I code in Python ;) .Shall add more functionality later on.