Scrapy.如何在开始爬行后更改蜘蛛设置？

Question

我无法在parse方法中更改spider设置.但绝对必须是一种方式.

例如:

class SomeSpider(BaseSpider):
    name = 'mySpider'
    allowed_domains = ['example.com']
    start_urls = ['http://example.com']
    settings.overrides['ITEM_PIPELINES'] = ['myproject.pipelines.FirstPipeline']
    print settings['ITEM_PIPELINES'][0]
    #printed 'myproject.pipelines.FirstPipeline'
    def parse(self, response):
        #...some code
        settings.overrides['ITEM_PIPELINES'] = ['myproject.pipelines.SecondPipeline']
        print settings['ITEM_PIPELINES'][0]
        # printed 'myproject.pipelines.SecondPipeline'
        item = Myitem()
        item['mame'] = 'Name for SecondPipeline'  

但!项目将由FirstPipeline处理.新的ITEM_PIPELINES参数不起作用.如何在开始抓取后更改设置？提前致谢!

Answer 1

如果您希望不同的蜘蛛具有不同的管道，您可以为蜘蛛设置管道列表属性，该属性定义该蜘蛛的管道。比在管道中检查是否存在：

class MyPipeline(object):

    def process_item(self, item, spider):
        if self.__class__.__name__ not in getattr(spider, 'pipelines',[]):
            return item
        ...
        return item

class MySpider(CrawlSpider):
    pipelines = set([
        'MyPipeline',
        'MyPipeline3',
    ])

如果您希望不同的项目由不同的管道处理，您可以这样做：

    class MyPipeline2(object):
        def process_item(self, item, spider):
            if isinstance(item, MyItem):
                ...
                return item
            return item