Missing scheme in request url

问题:

I've been stuck on this bug for a while, the following error message is as follows:

File "C:\Python27\lib\site-packages\scrapy-0.20.2-py2.7.egg\scrapy\http\request\__init__.py", line 61, in _set_url
            raise ValueError('Missing scheme in request url: %s' % self._url)
            exceptions.ValueError: Missing scheme in request url: h

Scrapy code:

    from scrapy.contrib.spiders import CrawlSpider, Rule
    from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
    from scrapy.selector import Selector
    from scrapy.http import Request
    from spyder.items import SypderItem

    import sys
    import MySQLdb
    import hashlib
    from scrapy import signals
    from scrapy.xlib.pydispatch import dispatcher

    # _*_ coding: utf-8 _*_

    class some_Spyder(CrawlSpider):
        name = "spyder"

        def __init__(self, *a, **kw):
            # catch the spider stopping
            # dispatcher.connect(self.spider_closed, signals.spider_closed)
            # dispatcher.connect(self.on_engine_stopped, signals.engine_stopped)

            self.allowed_domains = "domainname.com"
            self.start_urls = "http://www.domainname.com/"
            self.xpaths = '''//td[@class="CatBg" and @width="25%" 
                          and @valign="top" and @align="center"]
                          /table[@cellspacing="0"]//tr/td/a/@href'''

            self.rules = (
                Rule(SgmlLinkExtractor(restrict_xpaths=(self.xpaths))),
                Rule(SgmlLinkExtractor(allow=('cart.php?')), callback='parse_items'),
                )

            super(spyder, self).__init__(*a, **kw)

        def parse_items(self, response):
            sel = Selector(response)
            items = []
            listings = sel.xpath('//*[@id="tabContent"]/table/tr')

            item = IgeItem()
            item["header"] = sel.xpath('//td[@valign="center"]/h1/text()')

            items.append(item)
            return items

I'm pretty sure it's something to do with the url I'm asking scrapy to follow in the LinkExtractor. When extracting them in shell they looking something like this:

data=u'cart.php?target=category&category_id=826'

Compared to another url extracted from a working spider:

data=u'/path/someotherpath/category.php?query=someval'

I've had a look at a few questions on SO, such as Downloading pictures with scrapy but from reading it I think I may have a slightly different problem.

I also took a look at this - http://static.scrapy.org/coverage-report/scrapy_http_request___init__.html

which explains that the error is thrown up if self.urls is missing a ":", from looking at the start_urls I've defined I can't quite see why this error would show since the scheme is clearly defined.

Thanks for reading,

Toby

回答1:

change start_urls to:

self.start_urls = ["http://www.bankofwow.com/"]

回答2:

prepend url with 'http' or 'https'

回答3:

As @Guy answered earlier, start_urls attribute must be a list, the exceptions.ValueError: Missing scheme in request url: h message comes from that: the "h" in the error message is the first character of "http://www.bankofwow.com/", interpreted as a list (of characters)

allowed_domains must also be a list of domains, otherwise you'll get filtered "offsite" requests.

Change restrict_xpaths to

self.xpaths = """//td[@class="CatBg" and @width="25%" 
                    and @valign="top" and @align="center"]
                   /table[@cellspacing="0"]//tr/td"""

it should represent an area in the document where to find links, it should not be link URLs directly

From http://doc.scrapy.org/en/latest/topics/link-extractors.html#sgmllinkextractor

restrict_xpaths (str or list) – is a XPath (or list of XPath’s) which defines regions inside the response where links should be extracted from. If given, only the text selected by those XPath will be scanned for links.

Finally, it's customary to define these as class attributes instead of settings those in __init__:

from scrapy.contrib.spiders import CrawlSpider, Rule
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.selector import Selector
from scrapy.http import Request
from bow.items import BowItem

import sys
import MySQLdb
import hashlib
from scrapy import signals
from scrapy.xlib.pydispatch import dispatcher

# _*_ coding: utf-8 _*_

class bankOfWow_spider(CrawlSpider):
    name = "bankofwow"

    allowed_domains = ["bankofwow.com"]
    start_urls = ["http://www.bankofwow.com/"]
    xpaths = '''//td[@class="CatBg" and @width="25%"
                  and @valign="top" and @align="center"]
                  /table[@cellspacing="0"]//tr/td'''

    rules = (
        Rule(SgmlLinkExtractor(restrict_xpaths=(xpaths,))),
        Rule(SgmlLinkExtractor(allow=('cart.php?')), callback='parse_items'),
        )

    def __init__(self, *a, **kw):
        # catch the spider stopping
        # dispatcher.connect(self.spider_closed, signals.spider_closed)
        # dispatcher.connect(self.on_engine_stopped, signals.engine_stopped)
        super(bankOfWow_spider, self).__init__(*a, **kw)

    def parse_items(self, response):
        sel = Selector(response)
        items = []
        listings = sel.xpath('//*[@id="tabContent"]/table/tr')

        item = IgeItem()
        item["header"] = sel.xpath('//td[@valign="center"]/h1/text()')

        items.append(item)
        return items

回答4:

Scheme basically has a syntax like

scheme:[//[user:password@]host[:port]][/]path[?query][#fragment]

Examples of popular schemes include http(s), ftp, mailto, file, data, and irc. There could also be terms like about or about:blank we are somewhat familiar with.

It's more clear in the description on that same definition page:

                    hierarchical part
        ┌───────────────────┴─────────────────────┐
                    authority               path
        ┌───────────────┴───────────────┐┌───┴────┐
  abc://username:[e-mail]:123/path/data?key=value&key2=value2#fragid1
  └┬┘   └───────┬───────┘ └────┬────┘ └┬┘           └─────────┬─────────┘ └──┬──┘
scheme  user information     host     port                  query         fragment

  urn:example:mammal:monotreme:echidna
  └┬┘ └──────────────┬───────────────┘
scheme              path

In the question of Missing schemes it appears that there is [//[user:password@]host[:port]] part missing in

data=u'cart.php?target=category&category_id=826'

as mentioned above.

I had a similar problem where this simple concept would suffice the solution for me!

Hope this helps some.

回答5:

change start_urls to:

self.start_urls = ("http://www.domainname.com/",)

it should work.