Debugging ScraperWiki scraper (producing spurious integer)

Here is a scraper I created using Python on ScraperWiki:

import lxml.html
import re
import scraperwiki

pattern = re.compile(r'\s')
html = scraperwiki.scrape("http://www.shanghairanking.com/ARWU2012.html")
root = lxml.html.fromstring(html)
for tr in root.cssselect("#UniversityRanking tr:not(:first-child)"):
    if len(tr.cssselect("td.ranking")) > 0 and len(tr.cssselect("td.rankingname")) > 0:
        data = {
            'arwu_rank'  : str(re.sub(pattern, r'', tr.cssselect("td.ranking")[0].text_content())),
            'university' : tr.cssselect("td.rankingname")[0].text_content().strip()
        }
    # DEBUG BEGIN
    if not type(data["arwu_rank"]) is str:
        print type(data["arwu_rank"])
        print data["arwu_rank"]
        print data["university"]
    # DEBUG END
    if "-" in data["arwu_rank"]:
        arwu_rank_bounds  = data["arwu_rank"].split("-")
        data["arwu_rank"] = int( ( float(arwu_rank_bounds[0]) + float(arwu_rank_bounds[1]) ) * 0.5 )
    if not type(data["arwu_rank"]) is int:
        data["arwu_rank"] = int(data["arwu_rank"])
    scraperwiki.sqlite.save(unique_keys=['university'], data=data)

It works perfectly except when scraping the final data row of the table (the "York University" line), at which point instead of lines 9 through 11 of the code causing the string "401-500" to be retrieved from the table and assigned to data["arwu_rank"], those lines somehow seem instead to be causing the int 450 to be assigned to data["arwu_rank"]. You can see that I've added a few lines of "debugging" code to get a better understanding of what's going on, but also that that debugging code doesn't go very deep.

I have two questions:

1. What are my options for debugging scrapers run on the ScraperWiki infrastructure, e.g. for troubleshooting issues like this? E.g. is there a way to step through?
2. Can you tell me why the the int 450, instead of the string "401-500", is being assigned to data["arwu_rank"] for the "York University" line?

EDIT 6 May 2013, 20:07h UTC

The following scraper completes without issue, but I'm still unsure why the first one failed on the "York University" line:

import lxml.html
import re
import scraperwiki

pattern = re.compile(r'\s')
html = scraperwiki.scrape("http://www.shanghairanking.com/ARWU2012.html")
root = lxml.html.fromstring(html)
for tr in root.cssselect("#UniversityRanking tr:not(:first-child)"):
    if len(tr.cssselect("td.ranking")) > 0 and len(tr.cssselect("td.rankingname")) > 0:
        data = {
            'arwu_rank'  : str(re.sub(pattern, r'', tr.cssselect("td.ranking")[0].text_content())),
            'university' : tr.cssselect("td.rankingname")[0].text_content().strip()
        }
        # DEBUG BEGIN
        if not type(data["arwu_rank"]) is str:
            print type(data["arwu_rank"])
            print data["arwu_rank"]
            print data["university"]
        # DEBUG END
        if "-" in data["arwu_rank"]:
            arwu_rank_bounds  = data["arwu_rank"].split("-")
            data["arwu_rank"] = int( ( float(arwu_rank_bounds[0]) + float(arwu_rank_bounds[1]) ) * 0.5 )
        if not type(data["arwu_rank"]) is int:
            data["arwu_rank"] = int(data["arwu_rank"])
        scraperwiki.sqlite.save(unique_keys=['university'], data=data)

There's no easy way to debug your scripts on ScraperWiki, unfortunately it just sends your code in its entirety and gets the results back, there's no way to execute the code interactively.

I added a couple more prints to a copy of your code, and it looks like the if check before the bit that assigns data

if len(tr.cssselect("td.ranking")) > 0 and len(tr.cssselect("td.rankingname")) > 0:

doesn't trigger for "York University" so it will be keeping the int value (you set it later on) from the previous time around the loop.