Python爬虫：scrapy爬虫设置随机访问时间间隔

scrapy中有一个参数：DOWNLOAD_DELAY 或者 download_delay 可以设置下载延时，不过Spider类被初始化的时候就固定了，爬虫运行过程中没发改变。

随机延时，可以降低被封ip的风险

代码示例

random_delay_middleware.py

# -*- coding:utf-8 -*-

import logging
import random
import time


class RandomDelayMiddleware(object):
    def __init__(self, delay):
        self.delay = delay

    @classmethod
    def from_crawler(cls, crawler):
        delay = crawler.spider.settings.get("RANDOM_DELAY", 10)
        if not isinstance(delay, int):
            raise ValueError("RANDOM_DELAY need a int")
        return cls(delay)

    def process_request(self, request, spider):
        delay = random.randint(0, self.delay)
        logging.debug("### random delay: %s s ###" % delay)
        time.sleep(delay)

使用方式：

custom_settings = {
        "RANDOM_DELAY": 3,
        "DOWNLOADER_MIDDLEWARES": {
            "middlewares.random_delay_middleware.RandomDelayMiddleware": 999,
        }
    }

说明： RANDOM_DELAY: 下载随机延时范围，[0, RANDOM_DELAY] 比如上面我设置了3秒，那么随机延时范围将是[0, 3] 如果设置了DOWNLOAD_DELAY 那么，总的延时应该是两者之和：

total_delay = DOWNLOAD_DELAY + RANDOM_DELAY

更精确的说，应该是：

DOWNLOAD_DELAY + 0 < total_delay < DOWNLOAD_DELAY + RANDOM_DELAY