afurlan's blog

Some time ago I changed my default shell to use IPython instead of Bash. The IPython is a really great shell and IMHO has great advantages but for those who, like me, are completely addicted to the clear command, the IPython's clear is a huge disadvantage.

In IPython, the clear command clear varios data like input, output and directory histories but it doesn't clear the screen! You can take a look at the documentation of default function for the clear command below and see how it works:

afurlan@merlin:~$ from IPython.Extensions.clearcmd import clear_f
afurlan@merlin:~$ print clear_f.__doc__
 Clear various data (e.g. stored history data)

    %clear out - clear output history
    %clear in  - clear input history
    %clear shadow_compress - Compresses shadow history (to speed up ipython)
    %clear shadow_nuke - permanently erase all entries in shadow history
    %clear dhist - clear dir history

afurlan@merlin:~$

So I created a new function to extend the first one adding the option to clear the screen when no args were passed. If you'd like to do the same, add the following lines in your ~/.ipython/ipy_user_conf.py:

def new_clear_f(*args, **kwargs):
    ''' Extend the default clear function adding the option to
    clear the screen when no args were passed.'''
    if not args[1]:
            ip.system('clear')
    else:
            from IPython.Extensions.clearcmd import clear_f
            clear_f(*args, **kwargs)
            ip.expose_magic('clear', new_clear_f)
ip.expose_magic('clear', new_clear_f)

And now it all seems clear again. :)

As always: if you found some english bug, warn me and I'll be glad to fix it. :)

Some days ago Google released Go, its own open source programming language. Go is intended to be a simple, fast and safe programming language that promotes the users to write programs through concurrent and communicating lightweight processes. If want to know more about how to install and how to use Go, please take a look at its official site: http://golang.org.

Today I installed Go to play with it a little bit and (as I use to), after the world famous "hello world" code, I wrote a program to generate the fibonacci's sequence. Actually I wrote two versions of the same program, the first one is the most common fibonacci code:

package main

import "os"
import "fmt"
import "strconv"

func fib1(n int) int {
    if n < 0 { return 0; }
    if n < 2 { return n; }
    return fib1(n-2) + fib1(n-1);
}

func main() {
    if len(os.Args) < 2 {
            fmt.Printf("Usage: %s NUM\n", os.Args[0]);
            os.Exit(1);
    }
    n, _ := strconv.Atoi(os.Args[1]);
    fmt.Printf("%d\n", fib1(n));
}

And the second version is basically the same code but keeping a history of the known results:

package main

import "os"
import "fmt"
import "strconv"

func fib2(n int, hist *map[int]int) int {
    if n < 0 { return 0; }
    if n < 2 { return n; }
    _, found := (*hist)[n];
    if !found {
            (*hist)[n] = fib2(n-2, hist) + fib2(n-1, hist)
    }
    return (*hist)[n];
}

func main() {
    if len(os.Args) < 2 {
            fmt.Printf("Usage: %s NUM\n", os.Args[0]);
            os.Exit(1);
    }
    n, _ := strconv.Atoi(os.Args[1]);
    hist := make(map[int]int);
    fmt.Printf("%d\n", fib2(n, &hist));
}

Once you have finished these codes, it's always nice to see how different their execution time are:

afurlan@merlin:~$ time ./fib1 45
1134903170

real    0m43.979s
user    0m43.887s
sys     0m0.008s
afurlan@merlin:~$ time ./fib2 45
1134903170

real    0m0.004s
user    0m0.004s
sys     0m0.000s

Go is a very nice language, let's go to Go. :)

As always: if you found some english bug, warn me and I'll be glad to fix it. :)