UnicodeEncodeError after setting restrict_xpaths settings

Question

i'm new to python and scrapy. After setting restrict_xpaths settings to "//table[@class="lista"]" I've received following traceback. What's strange, by using other xpath rule the crawler works properly.

Traceback (most recent call last):
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/twisted/internet/base.py", line 800, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/twisted/internet/task.py", line 602, in _tick
    taskObj._oneWorkUnit()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/twisted/internet/task.py", line 479, in _oneWorkUnit
    result = self._iterator.next()
  File "/Library/Python/2.7/site-packages/scrapy/utils/defer.py", line 57, in <genexpr>
    work = (callable(elem, *args, **named) for elem in iterable)
--- <exception caught here> ---
  File "/Library/Python/2.7/site-packages/scrapy/utils/defer.py", line 96, in iter_errback
    yield it.next()
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spidermiddleware/offsite.py", line 23, in process_spider_output
    for x in result:
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spidermiddleware/referer.py", line 22, in <genexpr>
    return (_set_referer(r) for r in result or ())
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spidermiddleware/urllength.py", line 33, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spidermiddleware/depth.py", line 50, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spiders/crawl.py", line 73, in _parse_response
    for request_or_item in self._requests_to_follow(response):
  File "/Library/Python/2.7/site-packages/scrapy/contrib/spiders/crawl.py", line 52, in _requests_to_follow
    links = [l for l in rule.link_extractor.extract_links(response) if l not in seen]
  File "/Library/Python/2.7/site-packages/scrapy/contrib/linkextractors/sgml.py", line 124, in extract_links
    ).encode(response.encoding)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/encodings/iso8859_2.py", line 12, in encode
    return codecs.charmap_encode(input,errors,encoding_table)
exceptions.UnicodeEncodeError: 'charmap' codec can't encode character u'\xbb' in position 686: character maps to <undefined>

Here is MySpider Class.

from scrapy.contrib.spiders import CrawlSpider, Rule
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.selector import HtmlXPathSelector
from ds_crawl.items import DsCrawlItem

class MySpider(CrawlSpider):
    name = 'inside'
    allowed_domains = ['wroclaw.dlastudenta.pl']
    start_urls = ['http://wroclaw.dlastudenta.pl/stancje/']

    rules = (
        Rule(SgmlLinkExtractor(allow=('show_stancja'), restrict_xpaths=('//table[@class="lista"]')),  callback='parse_item', follow= True),)

    def parse_item(self, response):
        hxs = HtmlXPathSelector(response)
        titles = hxs.select("//p[@class='bbtext intextAd']")
        for titles in titles:
            item = DsCrawlItem()
            item['content'] = titles.select("text()").extract()
            print item

Any explanation of this error and help will be appreciated. Thank you.

Answer 1

That's a bug caused by the web page using the » entity which is translated by lxml to the unicode character \xbb and when you use the restrict_xpaths argument the link extractors encodes the content to the original encoding iso8859-2 which fails because \xbb is not valid character in that encoding.

This simple line reproduces the exception:

>>> u'\xbb'.encode('iso8859-2')
...
UnicodeEncodeError: 'charmap' codec can't encode character u'\xbb' in position 0: character maps to <undefined>

A workaround for this can be forcing to use utf8 for all responses. This can be done by a simple downloader middleware:

# file: myproject/middlewares.py

class ForceUTF8Response(object):
    """A downloader middleware to force UTF-8 encoding for all responses."""
    encoding = 'utf-8'

    def process_response(self, request, response, spider):
        # Note: Use response.body_as_unicode() instead of response.text in in Scrapy <1.0.
        new_body = response.text.encode(self.encoding)
        return response.replace(body=new_body, encoding=self.encoding)

In your settings:

DOWNLOADER_MIDDLEWARES = {
    'myproject.middlewares.ForceUTF8Response': 100,
}