Screen Scraping XPATH in HTML Agility Pack isn't delivering data.

c# html-agility-pack screen-scraping web-scraping


I'm attempting to write a screen scraper for Digikey that will allow our company to keep accurate track of pricing, part availability and product replacements when a part is discontinued. There seems to be a discrepancy between the XPATH that I'm seeing in Chrome Devtools as well as Firebug on Firefox and what my C# program is seeing.

The page that I'm scraping currently is

The code I'm currently using is pretty quick and dirty...

   //This function retrieves data from the digikey
   private static List<string> ExtractProductInfo(HtmlDocument doc)
       List<HtmlNode> m_unparsedProductInfoNodes = new List<HtmlNode>();
       List<string> m_unparsedProductInfo = new List<string>();

       //Base Node for part info
       string m_baseNode = @"//html[1]/body[1]/div[2]";

       //Write part info to list
       m_unparsedProductInfoNodes.Add(doc.DocumentNode.SelectSingleNode(m_baseNode + @"/table[1]/tr[1]/td[1]/table[1]/tr[1]/td[1]"));
       //More lines of similar form will go here for more info
       //this retrieves digikey PN

       foreach(HtmlNode node in m_unparsedProductInfoNodes)

       return m_unparsedProductInfo;

Although the path I'm using appears to be "correct" I keep getting NULL when I look at the list "m_unparsedProductInfoNodes"

Any idea what's going on here? I'll also add that if I do a "SelectNodes" on the baseNode it only returns a div with the only significant child being "cs=####" which seems to vary with browser user agents. If I try to use this in anyway (putting /cs=0 in the path for the unidentifiable browser) it pitches a fit insisting that my expression doesn't evaluate to a node set, but leaving them still leaves the problem of all data past div[2] is returned as NULL.

3/23/2010 3:37:04 PM

Popular Answer

Just for an update:

I switched from c# into a bit more friendly Python (my experience with programming is asm, c, and python, the whole OO thing was totally new) and managed to correct my xpath issues. The tag was indeed the problem, but luckily it's unique, so a little regular expression and a removed line and I was in good shape. I'm not sure why a tag like that breaks the XPATH though. If anyone has some insight I'd like to hear it.

3/26/2010 7:07:12 PM

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