class
CrawlSpider(Spider):
rules
=
()
def
__init__(
self
,
*
a,
*
*
kw):
super
(CrawlSpider,
self
).__init__(
*
a,
*
*
kw)
self
._compile_rules()
#首先调用parse()来处理start_urls中返回的response对象
#parse()则将这些response对象传递给了_parse_response()函数处理,并设置回调函数为parse_start_url()
#设置了跟进标志位True
#parse将返回item和跟进了的Request对象
def
parse(
self
, response):
return
self
._parse_response(response,
self
.parse_start_url, cb_kwargs
=
{}, follow
=
True
)
#处理start_url中返回的response,需要重写
def
parse_start_url(
self
, response):
return
[]
def
process_results(
self
, response, results):
return
results
#从response中抽取符合任一用户定义'规则'的链接,并构造成Resquest对象返回
def
_requests_to_follow(
self
, response):
if
not
isinstance
(response, HtmlResponse):
return
seen
=
set
()
#抽取之内的所有链接,只要通过任意一个'规则',即表示合法
for
n, rule
in
enumerate
(
self
._rules):
links
=
[l
for
l
in
rule.link_extractor.extract_links(response)
if
l
not
in
seen]
#使用用户指定的process_links处理每个连接
if
links
and
rule.process_links:
links
=
rule.process_links(links)
#将链接加入seen集合,为每个链接生成Request对象,并设置回调函数为_repsonse_downloaded()
for
link
in
links:
seen.add(link)
#构造Request对象,并将Rule规则中定义的回调函数作为这个Request对象的回调函数
r
=
Request(url
=
link.url, callback
=
self
._response_downloaded)
r.meta.update(rule
=
n, link_text
=
link.text)
#对每个Request调用process_request()函数。该函数默认为indentify,即不做任何处理,直接返回该Request.
yield
rule.process_request(r)
#处理通过rule提取出的连接,并返回item以及request
def
_response_downloaded(
self
, response):
rule
=
self
._rules[response.meta[
'rule'
]]
return
self
._parse_response(response, rule.callback, rule.cb_kwargs, rule.follow)
#解析response对象,会用callback解析处理他,并返回request或Item对象
def
_parse_response(
self
, response, callback, cb_kwargs, follow
=
True
):
#首先判断是否设置了回调函数。(该回调函数可能是rule中的解析函数,也可能是 parse_start_url函数)
#如果设置了回调函数(parse_start_url()),那么首先用parse_start_url()处理response对象,
#然后再交给process_results处理。返回cb_res的一个列表
if
callback:
#如果是parse调用的,则会解析成Request对象
#如果是rule callback,则会解析成Item
cb_res
=
callback(response,
*
*
cb_kwargs)
or
()
cb_res
=
self
.process_results(response, cb_res)
for
requests_or_item
in
iterate_spider_output(cb_res):
yield
requests_or_item
#如果需要跟进,那么使用定义的Rule规则提取并返回这些Request对象
if
follow
and
self
._follow_links:
#返回每个Request对象
for
request_or_item
in
self
._requests_to_follow(response):
yield
request_or_item
def
_compile_rules(
self
):
def
get_method(method):
if
callable
(method):
return
method
elif
isinstance
(method,
basestring
):
return
getattr
(
self
, method,
None
)
self
._rules
=
[copy.copy(r)
for
r
in
self
.rules]
for
rule
in
self
._rules:
rule.callback
=
get_method(rule.callback)
rule.process_links
=
get_method(rule.process_links)
rule.process_request
=
get_method(rule.process_request)
def
set_crawler(
self
, crawler):
super
(CrawlSpider,
self
).set_crawler(crawler)
self
._follow_links
=
crawler.settings.getbool(
'CRAWLSPIDER_FOLLOW_LINKS'
,
True
)