Source code analysis of scripy spider

Reptile basic reference Getting started with enterprise distributed crawler framework
The source code is shown below ：

• spider Of name Defined Scrapy How to locate ( And initialization ) spider, So its name Must be unique .name yes spider The most important attribute . The general practice is to use the website (domain) Named after the spider. for example , If spider Crawling mywebsite.com , The spider It's usually named mywebsite.

# The base class of all reptiles , User defined crawlers must inherit from this class 
class Spider(object_ref):
    name = None
    # initialization , Extract the crawler name ,start_urls
    def __init__(self, name=None, **kwargs):
        if name is not None:
            self.name = name
        elif not getattr(self, 'name', None):  #  If a reptile has no name , If the subsequent operation is interrupted, an error will be reported 
            raise ValueError("%s must have a name" % type(self).__name__)
​
        # python  Object or type through built-in members __dict__ To store member information 
        self.__dict__.update(kwargs)
​
        if not hasattr(self, 'start_urls'):
            self.start_urls = []​
​
    #  Print  Scrapy  After execution  log  Information 
    def log(self, message, level=log.DEBUG, **kw):
        log.msg(message, spider=self, level=level, **kw)
​​
    #  Judge the object object Does the property of exist , There is no assertion processing 
    def set_crawler(self, crawler):
        assert not hasattr(self, '_crawler'), "Spider already bounded to %s" % crawler
        self._crawler = crawler
​
    @property
    def crawler(self):
        assert hasattr(self, '_crawler'), "Spider not bounded to any crawler"
        return self._crawler
​
    @property
    def settings(self):
        return self.crawler.settings​
​
    # This method will read  start_urls  The address in , And generate a... For each address Request object , hand Scrapy Download and return to Response  This method is called only once 
    def start_requests(self):
        for url in self.start_urls:
            yield self.make_requests_from_url(url)
​​
    #start_requests() Call in , Actually generate Request Function of .
    #Request Object's default callback function is parse(), The way to submit is get
    def make_requests_from_url(self, url):
        return Request(url, dont_filter=True)
​​
    # default Request Object callback function , Process the returned response.
    # Generate Item perhaps Request object . The user must implement this class 
    def parse(self, response):
        raise NotImplementedError
​
    @classmethod
    def handles_request(cls, request):
        return url_is_from_spider(request.url, cls)
​
    def __str__(self):
        return "<%s %r at 0x%0x>" % (type(self).__name__, self.name, id(self))
    __repr__ = __str__

• allowed_domains： Contains spider Domain name allowed to crawl (domain) A list of , Optional .
• start_urls： initial URL Yuan Zu / list
• start_requests(self)： This method must return an iteratable object (iterable), When spider Start crawling and do not specify start_urls when , The method is called .
• parse(self, response)： When requested url When no callback function is specified for the return page , default Request Object callback function . Used to process web page returns response, And generate Item perhaps Request object .
• log(self, message[, level, component])： Use scrapy.log.msg() Method record (log)message. More data can be found in logging