Jim DeLaHunt, world-ready

Are you using PHP (or libGD) to generate PNG images?  Are you having problems getting your text anti-aliased, and also having your “transparent” colour recognised as transparent?  Well, I had that problem too.  libGD, the component which PHP uses to handle image operations, gives you a choice: you can have anti-aliased text, or a designated colour as transparent… but not both.  Here’s why, and what you can do about it.

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This post has been a long time in the making. A year ago, I started work on my Twanguages code. This was code to analyse a corpus of Twitter messages, and try to discern patterns about language use, geography, and character encoding.  I decided to use the Django web framework and the Python language for the Twanguages analysis code.  I know Python, but I was learning Django for the first time.

Django is really, really marvellous.  When I tried this expression, and got the Python array of records I was expecting,

q2 = TwUser.objects.annotate(ntweets=Count('twstatus')).filter(ntweets__gt=1)

I wrote in my log, “I think I just fell in love. Power and concision in a tool, awesome.”

But Django gave me fits.  It has its share of quirks to trap the unwary novice. Eventually I began writing notes about “Django gotchas” in my log.  Some of them are Django being difficult, or inadequate. Some are me being a clueless novice, and Django not rescuing me from my folly. But all of them were obstacles.  I share them in the hopes of helping another Django novice.

Here are my Django gotchas.  They are ranked from the most distressing to most benign. They apply to Django 1.1, the current version at the time. (As of August 2010, the current version is 1.2.1.) A couple of gotchas were addressed by Django 1.2, so I moved them down to a section of their own. The rest presumably still apply to Django 1.2, but I haven’t gone back to check.

1. API fails unhelpfully. I wrote a simple query expression like:

   S2 = models.TwStatus.objects.get( key )

   I got a lot of weird errors, e.g. “ValueError: too many values to unpack” (where key is string) and “TypeError: ‘long’ object is not iterable” (where key is long). I had made a mistake, of course; the call to get() should have a keyword argument of “id__exact” or the like, not a positional argument. The correct spelling is this:

   S2 = models.TwStatus.objects.get( id__exact=key )

   The gotcha is that Django’s .get() isn’t written defensively. It isn’t very robust to programmer errors. Instead of checking parameters and giving clear error messages, it lets bad parameters through, only to have them fail obscurely deep in the framework. If defensive programming of the Django API would slow it down too much in production, I’d love to have a debug mode I could invoke during development. Continue Reading »

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I just resolved a problem which has been an annoyance for two years. I’m posting the details as robobait in the hopes it will help others.

Our family network includes a Samba file server hosted on an NSLU2 server appliance by Linksys (now a part of Cisco). A long time ago we changed to the Unslung open firmware for the NSLU2 (or “Slug”, as we call it).    It’s a wonderful combination, powered by a rich assortment of free software created by many volunteers. I appreciate their efforts.

But two years ago, I moved my personal computing from a laptop running Mac OS X 10.3 to one running Mac OS X 10.5. On the new 10.5 laptop, I noticed that the NSLU2 failed to respect file modification times. That is, if I had a file created on Dec 1, 2007 on my laptop, and I dragged it to a Samba volume hosted on the NSLU2, then the time stamp on the copied file was changed to the present time. The Dec 1, 2007 modtime was lost. Similarly, if I used touch -t from the Mac OS X command line to change the timestamp on a file hosted on the NSLU2 Samba volume, the operation failed. If I tried  sudo touch -t, that succeeded, just until another client viewed the file — at which point the timestamp snapped to the present again. However, if I copied a file resident on the NSLU2 Samba volume to another location on the volume, the timestamp was preserved.

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I just figured out a solution for a problem setting up a piece of Windows freeware on my computer, and I’m recording it here as robobait so that others can benefit from it.

I use the wonderful Exact Audio Copy (EAC) software to rip my CDs to FLAC files, as part of moving our music collection onto a media server.  I had just uninstalled version 0.99pb3 (this thing has been “pre-beta” and version 0.99 for years!) and installed version 0.99pb5. I set the directory to which EAC writes its extracted files to be on my Samba file server. When I tried 0.99pb5, though, I observed that whenever I tried to copy tracks from the CD, an “Error Message” alert box would pop up, saying “File Creation Error !” What I expected, and what I recalled from using 0.99pb3, was that EAC would write the compressed files happily to the server directory.

The minimal test case to produce the error was to select one track from the CD, and then select the menu item “Action“… “Copy selected tracks” “Uncompressed“. The Windows system in question is a virtual machine running Windows XP on my Macbook Pro laptop.  I had set up EAC’s “Standard directory for extraction” to a UNC server path, let’s call it “\\samba\media\Music\untagged_flac\“.  I observed, by the way, that when I changed the destination directory to be something on my Windows C:\ drive, then EAC wrote the file with no problem. And interestingly, EAC had no trouble writing log files and cue files to the server directory using the UNC path, but it refused to write audio data files.

The workaround which succeeded for me was to map a drive letter to the UNC path. In my case, I mapped the letter “Z:\” to “\\samba\media\Music\“. Then, I set EAC’s “Standard directory for extraction” (under “EAC“… “EAC options“… “Directories” tab…) to “Z:\untagged_flac\“.  Then EAC happily wrote compressed music files to my network directory.

I think this write failure is a regression from 0.99pb3; I recall the UNC path working then. But I haven’t reinstalled 0.99pb3 to prove the point. If you try that experiment, please leave me a comment and tell me what you found.

There are other possible causes for the “File Creation Error !” alert box.  A couple I found were:

• Unpermitted leading “\” character in EAC’s “naming scheme” option (under “Filename” tab), per a hydrogenaudio thread “EAC: File Creation Error on first CD track”
• Filename or total file path too long (I don’t know the operative limit), per a hydrogenaudio thread “EAC pb5 directory problem causes File Creation Error”

May no-one else have to spend the time I spent diagnosing this problem! Happy exact audio copying!

P.S. my thanks to the developers of EAC, and of FLAC.exe, and all the other pieces of software in this marvelous free tool chain.

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One of the many nice touches of the Django framework is that it provides tools and instructions to make a standalone Django documentation set from its distribution.  (Django is an application framework for the Python language that helps with database access and web application.)  Standalone docs are great for people like me who work on a laptop and are sometimes off the net. But I’m using Mac OS X, I get my code through Macports, and Django’s instructions don’t quite cover this case.  So I just figured it out.  Here’s the tricks I needed.  Maybe it will help you.

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Recently, I remodelled a Joomla template for one of my clients.  As I was installing newer versions of the template, I noticed an error message started appearing on installation:

XML Parsing Error at 1:1. Error 4: Empty document

However, the installation seemed to be successful. And I had a valid templateDetails.xml file in my template’s .zip file. There was a Joomla! forum thread “XML Parsing Error at 1:1. Error 4: Empty document” dating from December 28, 2008 about this problem, so it wasn’t just me.

Here is my diagnosis of the problem, and my solution.  Since this is one of those problems that drove me crazy, I’m going to put my findings here in hopes that search engines will find it and bring it to others who might benefit from the tip. Hence, it’s tagged “robobait”.

The short answer: the error message comes from a metadata file named ._templateDetails.xml, which the Mac OX 10.5.x Finder inserted into the ZIP archive. This file didn’t have XML content, but the Joomla installer interpreted it as such. And the content it did have, happened to be the kind of invalid content that provoked an error message instead of silent failure. The immediate solution is to generate the ZIP file in such a way that there is no metadata file named ._templateDetails.xml . Long-term, it would be nice if Joomla! would not display an error message in this situation.

Read on for more about the problem, the diagnosis, and possible solutions. Continue Reading »

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