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"""
Spider Middleware manager
See documentation in docs/topics/spider-middleware.rst
"""
from twisted.python.failure import Failure
from scrapy.middleware import MiddlewareManager
from scrapy.utils.defer import mustbe_deferred
from scrapy.utils.conf import build_component_list
def _isiterable(possible_iterator):
return hasattr(possible_iterator, '__iter__')
class SpiderMiddlewareManager(MiddlewareManager):
component_name = 'spider middleware'
@classmethod
def _get_mwlist_from_settings(cls, settings):
return build_component_list(settings['SPIDER_MIDDLEWARES_BASE'], \
settings['SPIDER_MIDDLEWARES'])
def _add_middleware(self, mw):
super(SpiderMiddlewareManager, self)._add_middleware(mw)
if hasattr(mw, 'process_spider_input'):
self.methods['process_spider_input'].append(mw.process_spider_input)
if hasattr(mw, 'process_spider_output'):
self.methods['process_spider_output'].insert(0, mw.process_spider_output)
if hasattr(mw, 'process_spider_exception'):
self.methods['process_spider_exception'].insert(0, mw.process_spider_exception)
def scrape_response(self, scrape_func, response, request, spider):
exit fname = lambda f:'%s.%s' % (f.im_self.__class__.__name__, f.im_func.__name__)
def process_spider_input(response):
for method in self.methods['process_spider_input']:
try:
result = method(response=response, spider=spider)
assert result is None, \
'Middleware %s must returns None or ' \
'raise an exception, got %s ' \
% (fname(method), type(result))
except:
return scrape_func(Failure(), request, spider)
return scrape_func(response, request, spider)
def process_spider_exception(_failure):
exception = _failure.value
57 for method in self.methods['process_spider_exception']:
result = method(response=response, exception=exception, spider=spider)
assert result is None or _isiterable(result), \
'Middleware %s must returns None, or an iterable object, got %s ' % \
(fname(method), type(result))
50 if result is not None:
return result
return _failure
def process_spider_output(result):
for method in self.methods['process_spider_output']:
result = method(response=response, result=result, spider=spider)
assert _isiterable(result), \
'Middleware %s must returns an iterable object, got %s ' % \
(fname(method), type(result))
return result
dfd = mustbe_deferred(process_spider_input, response)
dfd.addErrback(process_spider_exception)
dfd.addCallback(process_spider_output)
return dfd
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