Scrapy请求不会被解析

ping example.com
curl -I example.com

import scrapy

class ExampleSpider(scrapy.Spider):
    name = 'example'
    start_urls = ['http://example.com']

    def start_requests(self):
        for url in self.start_urls:
            yield scrapy.Request(url, headers={
                'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3'
            })

class ExampleSpider(scrapy.Spider):
    name = 'example'
    start_urls = ['http://example.com']

    def parse(self, response):
        title = response.xpath('//title/text()').get()
        yield {'title': title}

import scrapy

class ExampleSpider(scrapy.Spider):
    name = 'example'
    start_urls = ['http://example.com']

    custom_settings = {
        'DOWNLOAD_DELAY': 2,  # 设置下载延迟
        'ROBOTSTXT_OBEY': True,  # 遵守robots.txt规则
    }

    def start_requests(self):
        for url in self.start_urls:
            yield scrapy.Request(url)

import scrapy

class ExampleSpider(scrapy.Spider):
    name = 'example'
    start_urls = ['http://example.com']

    def start_requests(self):
        for url in self.start_urls:
            yield scrapy.Request(url)

    def parse(self, response):
        self.logger.debug('Parsing URL: %s', response.url)
        title = response.xpath('//title/text()').get()
        yield {'title': title}