GUI programming with Matplotlib, Tkinter and threads

This is probably old hat for most python programmers, but it just never became important enough for me until now. I'm currently writing a script for calculating A WHOLE BUNCH of radiative transfer models, and needed a way to visualize my results right away so I could tune my experiment at run-time. (For those who have some idea on model calculations, I'm searching a HUGE parameter space, and needed some quick-n-dirty methods to find my way around)

Eventually I ended up building a GUI frontend using Tkinter (because it's available with all Python distributions) and Matplotlib. Naturally I also had to figure out how threading is used in Python. Check out my Matplotlib wiki page for some recipes.

Covariant derivatives, contravariant tensors, affine connections... argh!

All the posts on MathWorld (here, here and others) written with fancy symbol generation and truckload of ads weren't as much help as the single article on MathPages written in plain HTML with goofed up inline symbols (and no ads!).

But I know what I really need is a good textbook.

Have I given in?

IronPython

Wheels

Very country-ish for what you usually expect from the Foo Fighters, but I love this song!

I feel my temperature rising...

Hilarious

Something's wrong though -- this is totally NOT Interpol. It's sort of a behind the scenes for the Rollins Band. Henry Rollins actually played a part in Johnny Mnemonic!!! Wow!

What a party!

Garage band

Bizarre Love Triangle

Original version by New Order

Cover by Frente!

Cover by Stabbing Westward (my favorite)

Interpolation with SciPy

This didn't take long, thanks to SciPy.

from scipy.interpolate import interpolate as interp

xa = [i * 10 for i in range(10)]
ya = [200.0 + 1.5 * x for x in xa]

iobj = interp.interp1d(xa, ya)
i_xa = [i for i in range(90)]
i_ya = [iobj(x) for x in i_xa]

import pylab as pl
pl.plot(xa, ya, "o")
pl.plot(i_xa, i_ya, "-")
pl.ylim(0, 1000)
pl.show()

A portable way to pass a string to C as a macro

#define STRINGIZE_(x) #x
#define STRINGIZE(x) STRINGIZE_(x)

And call STRINGIZE(x) in subsequent code. This is useful when using the -D option in gcc -- without STRINGIZE(), extra double-quotes (\") must be added in order to pass strings as macros from the command line.

Conditional expression in Python

It has bothered me for a long time that Python does not provide a conditional expression operator similar to the ?: operator used in C. But by some fortune, I ran across this Python snippet:

("False", "True")[var == True]

which does exactly the same as what you would write in C

var ? "True" : "False"

What a relief!

Erase/Replace

新的一年開始了。

我不要再害怕。

還要活的更從容。

這是這一年的新希望（似乎比往年成熟些？）。唸研究所，不論是知識上或是生活上都真的讓我學到很多很多；假如一直這樣下去，第一個目標也許可以達成一大部分。第二個目標似乎困難許多，但某種程度上也是建立在第一個目標上的吧。

繼續努力。

Regex for matching floating point numbers

As simple as it sounds, there doesn't seem to be a standard regular expression for matching floating point numbers -- for some reason everyone seems to have their own preference: scientific notation or not, decimal points in the exponent or not... etc. Currently I'm settling with

([-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]*\.?[0-9]+)?)

Actually for my purposes, I also need an optional unit, so I'm really using this

([-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]*\.?[0-9]+)?)([a-zA-Z]*)

Preventing string truncation with snprintf()

One issue with using snprintf() (the buffer-overrun-preventing version of sprintf()) is that since the size of the char[] we're trying to "print" into is limited, truncation would occur if the string is longer than the char[] size. Yet after studying the manual carefully, I noticed that snprintf() actually returns the length of the resultant string, regardless of the size of the buffer. Below is a simple demonstration of how to prevent truncation with this feature and dynamical allocation of the character buffer.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
   #define NC 10
   #define ALONGSTRING "A long string of nonsense that would've been truncated."

   size_t len;
   char *string = calloc(NC, sizeof(*string));

   len = snprintf(string, NC, ALONGSTRING);

   printf("Truncated string: '%s'\n", string);

   if(len >= NC) {
       string = realloc(string, (len + 1) * sizeof(*string));
       snprintf(string, len + 1, ALONGSTRING);
   }

   printf("Non-truncated string: '%s'\n", string);

   free(string);

   return 0;
}