When passing data to a web site, especially via "GET" requests (e.g. calling + stringWithContentsOfURL:encoding:error:) it's important to ensure content is properly escaped. This is also true on the iPhone when you are attempting to use a "mailto:" URL to invoke the native e-mail client from your app.

One obvious way to do this is by calling NSString's "- (NSString *)stringByAddingPercentEscapesUsingEncoding:(NSStringEncoding)encoding" method. While this does a good job, it is not perfect and will miss things like "/", which may make some web services cry. The best way to do this encoding is to use:

CFStringRef CFURLCreateStringByAddingPercentEscapes (
   CFAllocatorRef allocator,
   CFStringRef originalString,
   CFStringRef charactersToLeaveUnescaped,
   CFStringRef legalURLCharactersToBeEscaped,
   CFStringEncoding encoding
);

This method lets you specify what you want encoded and what you want left raw. I threw together a really quick sample command line tool to show you the difference. Here are the salient lies:

NSString *url = @"<b>some HTML content</b> <a href=\"http://theresurgence.com/search/node/bible\">study materials</a>" ;

NSLog(@"Original text: [%@]", url) ;

NSLog(@"NSString percent escapes: [%@]",
      [ url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]) ;

NSLog(@"CFURL percent escapes: [%@]",
      CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
          (CFStringRef)url, NULL, CFSTR("!*'();:@&=+$,/?%#[]"), kCFStringEncodingUTF8));

And, here is the output:

Original text: [<b>some HTML content</b> <a href="http://theresurgence.com/search/node/bible">study materials</a>]
NSString percent escapes: [%3Cb%3Esome%20HTML%20content%3C/b%3E%20%3Ca%20href=%22http://theresurgence.com/search/node/bible%22%3Estudy%20materials%3C/a%3E]
CFURL percent escapes: [%3Cb%3Esome%20HTML%20content%3C%2Fb%3E%20%3Ca%20href%3D%22http%3A%2F%2Ftheresurgence.com%2Fsearch%2Fnode%2Fbible%22%3Estudy%20materials%3C%2Fa%3E]

Big difference without tons of additional code. Plus, you can use CFURLCreateStringByReplacingPercentEscapesUsingEncoding just as easily to unescape any string.

- (NSString *)flattenHTML:(NSString *)html {

    NSScanner *theScanner;
    NSString *text = nil;

    theScanner = [NSScanner scannerWithString:html];

    while ([theScanner isAtEnd] == NO) {

        // find start of tag
        [theScanner scanUpToString:@"<" intoString:NULL] ; 

        // find end of tag
        [theScanner scanUpToString:@">" intoString:&text] ;

        // replace the found tag with a space
        //(you can filter multi-spaces out later if you wish)
        html = [html stringByReplacingOccurrencesOfString:
                           [ NSString stringWithFormat:@"%@>", text]
                     withString:@" "];

    } // while //
    
    return html;

}

Python on the Mac is a mixed blessing. On one hand, it makes app development much easier. On the other hand, it limits the deployment to OX X 10.5 (Leopard) unless you do some wrangling.

I made an Objective-C version of the "desktop widget" which is available for download now. Most likely, I will not update this version and I have not tested on Tiger yet. If you do test it and it does work (or fails miserably), please drop a note in the comments.

Cocoa is cool and Objective-C is a great language, but I like/prefer Python and the PyObjC bridge makes my life easier and programming actually interesting/fun for me.

This Xcode project is an example of how easy it is to create useful custom views in PyObjC with an example of a graph view that displays a circular queue/buffer. Everything is done starting with an Xcode project which is available for download (76KB compressed archive) and modification. Here is a preview of what you can use out of the box:

The easiest and smallest part of the project is the RingBuffer class that implements a very simple circular queue/buffer and provides direct access to the list that stores the information:

#
# RingBuffer.py

class RingBuffer:

    def __init__(self, size):
        """ init with # of elements in the queue """
        self.data = [ None for i in xrange(size)  ]

    def append(self, x):
        """ take away one and put one in """
        self.data.pop(0)
        self.data.append(x)

    def get(self):
        """ return the list so we can manipulate it """
        return self.data

There's not a lot of rocket science there, but it's amazing how much code you can eliminate by taking advantage of Python's inherent capabilities. In this case, list initialization is a breeze and removal/insertion of new elements could not be easier.

Next up is the CBGraphView class itself: