Simon Willison’s Weblog

Converting links without regular expressions

I pair-programmed this code with Natalie just over a month ago, and I’ve now added it to my Kansas blog simplified comments system as mentioned earlier.

A better way of entering dates

The CreativityGoblin dropped in on me today, and as a result I’ve been tackling the challenge of entering dates in to a web application. In the past, I’ve used DHTML calendar widgets for this purpose (my favourite is Mishoo’s highly configurable, standards compliant JS Calendar) but while widgets like this have a great deal of “wow” factor I’m not convinced that they are the best entry mechanism when it comes to raw user speed. Today’s experiment was partially inspired by PHP’s strtotime function, which accepts a string in a wide variety of formats and converts it in to a time.

“sexeger”[::-1]

Via Ned Batchelder, an article on Reversing Regular Expressions from Perl.com. Otherwise known as Sexeger, these offer a performance boost over normal regular expressions for certain tasks. The basic idea is pretty simple: searching backwards through a string using a regular expression can be a messy business, but by reversing both the string and the expression, running it, then reversing the result far better performance can be achieved (reversing a string is a relatively inexpensive operation). The example code is in Perl, but I couldn’t resist trying it in Python. The challenge is to find the last number occurring in a string.

Clearout

• Tristan Louis’ RSS to Necho convertor puts paid to the idea that the success of one format will be detrimental to the usefulness of the other.
• O’Reilly’s RegExp Power series (part one and part two) demonstrate some powerful tricks for use with Perl compatible regular expressions.
• Norman Walsh explains Content Negotiation and some of the pitfalls with modern browser implementations.
• So that’s what happened to Digitiser. See also a Digitiser Tribute and a Mr Biffo interview from 2001 for background information. I cuss you bad.
• George Orwell: Politics and the English Language
• Clay Shirky: A Group Is Its Own Worst Enemy. The title is misguiding; this is an essay about how online groups behave and how to look after them.
• A Java HttpClient Class.
• Some good stuff on Boxes and Arrows: Ten Quotable Moments: Challenges and Responses for UI Designers and Views and Forms: Principles of Task Flow for Web Applications (Part 1).
• Inside our notions of “document” and Inside our documents II—the Runoff model.
• 5 days worth of XSLT observations from Simon St. Laurent: One, Two, Three, Four, Five.
• Windows programming with open source tools: Minimalist GNU For Windows and Win32 Programming with GNU C and C++.

Safely consuming RSS: RegExps don’t cut it

Mark Pilgrim highlights the severe security issues introduced by RSS aggregators that display potentially unsafe HTML, often executing it in the “secure zone” generally reserved for trusted local documents. Mark suggests a number of dangerous tags and attributes that should be removed before display. Unsurprisingly, regular expressions have cropped up in the comments as the suggested solution. Jamie Zawinsky famously once posted the following to comp.lang.emacs:

Verbose Regular Expressions

Ned Batchelder describes Verbose Python regular expressions. This is one of the things I’ve known about (as in known that they exist) for ages but have never got around to using. I’ve been working with some pretty heavy regular expressions recently that could really do with the clarity of being defined in verbose format with comments.

UltraEdit regular expressions

Every now and then I find myself needing to use a regular expression in UltraEdit, and whenever I do I invariably have to spend five minutes re-reading that section of the manual to remind myself how its syntax differs from more traditional regular expressions. This time, I’m recording the result in the hope that it might jog my memory next time I need to use them.