Tag Archives: programming - Page 3

Beware the locale

Posted by Silveira on 22 February, 2010 No comments

Today I was programming a toString method for a class widely used in a application, using the very useful String.format that provides a C’s like printf formatter.

@Override
public String toString() {
   return String.format("VO[a: %.1f, b: %.1f, c: %.1f]", a, b, a+b);
}

%.1f means a float with one digit precision after the dot separator. The code produces something like:

VO[a: 1.0, b: 2.0, c: 3.0]

The problem arises when running a JUnit test on this method wrote using a regular expression to extract the values from the String to test it correctness. We cannot assume that the dot will be always the separator for displaying a float value, in my locale pt_BR would be a comma. So the output would be:

VO[a: 1,0, b: 2,0, c: 3,0]

For a predictable output we can set a Locale for String.format:

Locale en = new Locale("en");
return String.format(en, "VO[a: %.1f, b: %.1f, c: %.1f]", a, b, a+b);

So it will always use the dot as common separator. Of course you should follow and respect the localization and internationalization efforts in others moments but in this toString case we are using it internally for debug and unitary testing so we can set a English default locale for safety reasons.

Miojo Script

Posted by Silveira on 28 January, 2010 1 comment

O pre-requisito é o notify-send, um utilitário de linha de comando do libnotify. No Ubuntu:

sudo aptitude install libnotify-bin

E aqui o script em si:

sleep 5m; notify-send "aviso" "tirar o miojo do fogo"

Pronto, depois de cinco minutos isso vai aparecer:

Easily Sortable Date and Time Representation

Posted by Silveira on 20 January, 2010 No comments

I was looking for a date and time representation useful for registering stock quotes in a simple plain file.

I found that the standard ISO 8601 is just the answer for this, it’s called “Data elements and interchange formats — Information interchange — Representation of dates and times”. Here is a example:

2010-01-20 22:14:38

There’s this good article from Markus Kuhn, “A summary of the international standard date and time notation”. This notation allow us to using simple lexicographical order the events.

Some examples of how to do this in Python (thanks for the Jochen Voss article “Date and Time Representation in Python”) The first for displaying the current date and time:

from time import strftime
print strftime("%Y-%m-%d %H:%M:%S")
# 2010-01-20 22:34:22

Another possibility is using strftime from datetime object.

from datetime import datetime
now = datetime.datetime.now()
print now.strftime("%Y-%m-%d %H:%M:%S")
# 2010-01-20 22:12:31

Is that. Using this notation in the begging of each line is easy to sort them in any language or using the unix sort.

Java Font List

Posted by Silveira on 5 January, 2010 Comments Off

Here’s a program that lists fonts available in your JVM. You can also set the environment variable JAVA_FONTS to specify the font directory.

import java.awt.GraphicsEnvironment;
 
public class ListFonts {
	public static void main(String args[]){
		GraphicsEnvironment e = GraphicsEnvironment.getLocalGraphicsEnvironment();
		for(String font:e.getAvailableFontFamilyNames()){
			System.out.println(font);
		}
	}
}

By using pipes you can count how many fonts you have:

java ListFonts|wc -l

On my Ubuntu machine here I got 556 because I use those excellent, free and indispensable Larabie Fonts.

For looking up for a font with “sans” in its name, using a case insensitive grep:

java ListFonts|grep -i “sans”

I get a list like this:

DejaVu Sans
DejaVu Sans Condensed
DejaVu Sans Light
DejaVu Sans Mono
FreeSans

Python Fast XML Parsing

Posted by Silveira on 25 December, 2009 2 comments

Here is a useful tip on Python XML decoding.

I was extending xml.sax.ContentHandler class in a example to decode maps for a Pygame application when my connection went down and I noticed that the program stop working raising a exception regarded a call to urlib (a module for retrieve resources by url). I noticed that the module was getting the remote DTD schema to validate the XML.

<!DOCTYPE map SYSTEM "http://mapeditor.org/dtd/1.0/map.dtd">

This is not a requirement for my applications and it’s a huge performance overhead when works (almost 1 second for each map loaded) and when the applications is running in a environment without Internet it just waits for almost a minute and then fail with the remain decoding. A dirty workaround is open the XML file and get rid of the line containing the DTD reference.

But the correct way to programming XML decoding when we are not concerned on validate a XML schema is just the xml.parsers.expat. Instead of using a interface you just have to set some callback functions with the behaviors we want. This is a example from the documentation:

import xml.parsers.expat
 
# 3 handler functions
def start_element(name, attrs):
    print 'Start element:', name, attrs
def end_element(name):
    print 'End element:', name
def char_data(data):
    print 'Character data:', repr(data)
 
p = xml.parsers.expat.ParserCreate()
 
p.StartElementHandler = start_element
p.EndElementHandler = end_element
p.CharacterDataHandler = char_data
 
p.Parse("""<?xml version="1.0"?>
<parent id="top"><child1 name="paul">Text goes here</child1>
<child2 name="fred">More text</child2>
</parent>""", 1)

The output:

Start element: parent {'id': 'top'}
Start element: child1 {'name': 'paul'}
Character data: 'Text goes here'
End element: child1
Character data: '\n'
Start element: child2 {'name': 'fred'}
Character data: 'More text'
End element: child2
Character data: '\n'
End element: parent

Pygame: Running Orcs

Posted by Silveira on 11 December, 2009 1 comment

Here is a Pygame Sprite animation using the approach presented by Joe Wreschnig and Nicolas Crovatti. It’s not yet exactly what I need but is very suitable.

import pygame, random
from pygame.locals import *
 
class Char(pygame.sprite.Sprite):
	x,y = (100,0)
	def __init__(self, img, frames=1, modes=1, w=32, h=32, fps=3):
		pygame.sprite.Sprite.__init__(self)
		original_width, original_height = img.get_size()
		self._w = w
		self._h = h
		self._framelist = []
		for i in xrange(int(original_width/w)):
			self._framelist.append(img.subsurface((i*w,0,w,h)))
		self.image = self._framelist[0]		
		self._start = pygame.time.get_ticks()
		self._delay = 1000 / fps
		self._last_update = 0
		self._frame = 0
		self.update(pygame.time.get_ticks(), 100, 100)	
 
	def set_pos(self, x, y):
		self.x = x
		self.y = y
 
	def get_pos(self):
		return (self.x,self.y)
 
	def update(self, t, width, height):
		# postion
		self.y+=1
		if(self.y>width):
			self.x = random.randint(0,height-self._w)
			self.y = -self._h
 
		# animation
		if t - self._last_update > self._delay:
			self._frame += 1
			if self._frame >= len(self._framelist):
				self._frame = 0
			self.image = self._framelist[self._frame]
			self._last_update = t
 
SCREEN_W, SCREEN_H = (320, 320)
 
def main():
	pygame.init()
	screen = pygame.display.set_mode((SCREEN_W, SCREEN_H))
	background = pygame.image.load("field.png")
	img_orc = pygame.image.load("orc.png")
	orc = Char(img_orc, 4, 1, 32, 48)
	while pygame.event.poll().type != KEYDOWN:
		screen.blit(background, (0,0))
		screen.blit(orc.image,  orc.get_pos())
		orc.update(pygame.time.get_ticks(), SCREEN_W, SCREEN_H)
		pygame.display.update()
		pygame.time.delay(10)
 
if __name__ == '__main__': main()