python - 在 urllib2 中缓存？

Question

使用我忽略的 urllib2 时，是否有一种简单的方法来缓存内容，或者我必须自己滚动？

Answer 1

如果您不介意在稍低的级别上工作，httplib2 ( https://github.com/httplib2/httplib2 ) 是一个包含缓存功能的优秀 HTTP 库。

Answer 2

这个 ActiveState Python 配方可能会有所帮助： http ://code.activestate.com/recipes/491261/

Answer 3

您可以使用装饰器功能，例如：

class cache(object):
    def __init__(self, fun):
        self.fun = fun
        self.cache = {}

    def __call__(self, *args, **kwargs):
        key  = str(args) + str(kwargs)
        try:
            return self.cache[key]
        except KeyError:
            self.cache[key] = rval = self.fun(*args, **kwargs)
            return rval
        except TypeError: # incase key isn't a valid key - don't cache
            return self.fun(*args, **kwargs)

并按照以下方式定义一个函数：

@cache
def get_url_src(url):
    return urllib.urlopen(url).read()

这是假设您不关注 HTTP 缓存控制，而只是想在应用程序运行期间缓存页面

Answer 4

我一直在使用 httplib2（它在处理 HTTP 缓存和身份验证方面做得很好）和 urllib2（它位于 stdlib 中，具有可扩展的接口并支持 HTTP 代理服务器）之间纠结。

ActiveState 配方开始向 urllib2 添加缓存支持，但只是以非常原始的方式。它无法实现存储机制的可扩展性，无法对文件系统支持的存储进行硬编码。它也不支持 HTTP 缓存标头。

为了将 httplib2 缓存和 urllib2 可扩展性的最佳特性结合在一起，我调整了 ActiveState 配方以实现与 httplib2 中的大部分相同的缓存功能。该模块在 jaraco.net 中为jaraco.net.http.caching。链接指向在撰写本文时存在的模块。虽然该模块目前是较大的 jaraco.net 包的一部分，但它没有包内依赖项，因此请随意将模块拉出并在您自己的项目中使用它。

或者，如果你有 Python 2.6 或更高版本，你可以easy_install jaraco.net>=1.3使用 CachingHandler 和caching.quick_test().

"""Quick test/example of CacheHandler"""
import logging
import urllib2
from httplib2 import FileCache
from jaraco.net.http.caching import CacheHandler

logging.basicConfig(level=logging.DEBUG)
store = FileCache(".cache")
opener = urllib2.build_opener(CacheHandler(store))
urllib2.install_opener(opener)
response = opener.open("http://www.google.com/")
print response.headers
print "Response:", response.read()[:100], '...\n'

response.reload(store)
print response.headers
print "After reload:", response.read()[:100], '...\n'

请注意，jaraco.util.http.caching 没有为缓存的后备存储提供规范，而是遵循 httplib2 使用的接口。因此，httplib2.FileCache 可以直接与 urllib2 和 CacheHandler 一起使用。此外，为 httplib2 设计的其他后备缓存应该可供 CacheHandler 使用。

Answer 5

我正在寻找类似的东西，并遇到了danivo 发布的“Recipe 491261: Caching and throttling for urllib2”。问题是我真的不喜欢缓存代码（大量重复，大量手动加入文件路径而不是使用 os.path.join，使用静态方法，非常 PEP8'sih，以及我试图避免的其他事情）

代码稍微好一点（无论如何我认为），并且在功能上大致相同，只是添加了一些内容 - 主要是“recache”方法（示例用法可以在此处查看，或在if __name__ == "__main__":代码末尾的部分中查看）。

最新版本可以在http://github.com/dbr/tvdb_api/blob/master/cache.py找到，我将它粘贴在这里以供后代使用（删除了我的应用程序特定的标头）：

#!/usr/bin/env python
"""
urllib2 caching handler
Modified from http://code.activestate.com/recipes/491261/ by dbr
"""

import os
import time
import httplib
import urllib2
import StringIO
from hashlib import md5

def calculate_cache_path(cache_location, url):
    """Checks if [cache_location]/[hash_of_url].headers and .body exist
    """
    thumb = md5(url).hexdigest()
    header = os.path.join(cache_location, thumb + ".headers")
    body = os.path.join(cache_location, thumb + ".body")
    return header, body

def check_cache_time(path, max_age):
    """Checks if a file has been created/modified in the [last max_age] seconds.
    False means the file is too old (or doesn't exist), True means it is
    up-to-date and valid"""
    if not os.path.isfile(path):
        return False
    cache_modified_time = os.stat(path).st_mtime
    time_now = time.time()
    if cache_modified_time < time_now - max_age:
        # Cache is old
        return False
    else:
        return True

def exists_in_cache(cache_location, url, max_age):
    """Returns if header AND body cache file exist (and are up-to-date)"""
    hpath, bpath = calculate_cache_path(cache_location, url)
    if os.path.exists(hpath) and os.path.exists(bpath):
        return(
            check_cache_time(hpath, max_age)
            and check_cache_time(bpath, max_age)
        )
    else:
        # File does not exist
        return False

def store_in_cache(cache_location, url, response):
    """Tries to store response in cache."""
    hpath, bpath = calculate_cache_path(cache_location, url)
    try:
        outf = open(hpath, "w")
        headers = str(response.info())
        outf.write(headers)
        outf.close()

        outf = open(bpath, "w")
        outf.write(response.read())
        outf.close()
    except IOError:
        return True
    else:
        return False

class CacheHandler(urllib2.BaseHandler):
    """Stores responses in a persistant on-disk cache.

    If a subsequent GET request is made for the same URL, the stored
    response is returned, saving time, resources and bandwidth
    """
    def __init__(self, cache_location, max_age = 21600):
        """The location of the cache directory"""
        self.max_age = max_age
        self.cache_location = cache_location
        if not os.path.exists(self.cache_location):
            os.mkdir(self.cache_location)

    def default_open(self, request):
        """Handles GET requests, if the response is cached it returns it
        """
        if request.get_method() is not "GET":
            return None # let the next handler try to handle the request

        if exists_in_cache(
            self.cache_location, request.get_full_url(), self.max_age
        ):
            return CachedResponse(
                self.cache_location,
                request.get_full_url(),
                set_cache_header = True
            )
        else:
            return None

    def http_response(self, request, response):
        """Gets a HTTP response, if it was a GET request and the status code
        starts with 2 (200 OK etc) it caches it and returns a CachedResponse
        """
        if (request.get_method() == "GET"
            and str(response.code).startswith("2")
        ):
            if 'x-local-cache' not in response.info():
                # Response is not cached
                set_cache_header = store_in_cache(
                    self.cache_location,
                    request.get_full_url(),
                    response
                )
            else:
                set_cache_header = True
            #end if x-cache in response

            return CachedResponse(
                self.cache_location,
                request.get_full_url(),
                set_cache_header = set_cache_header
            )
        else:
            return response

class CachedResponse(StringIO.StringIO):
    """An urllib2.response-like object for cached responses.

    To determine if a response is cached or coming directly from
    the network, check the x-local-cache header rather than the object type.
    """
    def __init__(self, cache_location, url, set_cache_header=True):
        self.cache_location = cache_location
        hpath, bpath = calculate_cache_path(cache_location, url)

        StringIO.StringIO.__init__(self, file(bpath).read())

        self.url     = url
        self.code    = 200
        self.msg     = "OK"
        headerbuf = file(hpath).read()
        if set_cache_header:
            headerbuf += "x-local-cache: %s\r\n" % (bpath)
        self.headers = httplib.HTTPMessage(StringIO.StringIO(headerbuf))

    def info(self):
        """Returns headers
        """
        return self.headers

    def geturl(self):
        """Returns original URL
        """
        return self.url

    def recache(self):
        new_request = urllib2.urlopen(self.url)
        set_cache_header = store_in_cache(
            self.cache_location,
            new_request.url,
            new_request
        )
        CachedResponse.__init__(self, self.cache_location, self.url, True)


if __name__ == "__main__":
    def main():
        """Quick test/example of CacheHandler"""
        opener = urllib2.build_opener(CacheHandler("/tmp/"))
        response = opener.open("http://google.com")
        print response.headers
        print "Response:", response.read()

        response.recache()
        print response.headers
        print "After recache:", response.read()
    main()

Answer 6

Yahoo Developer Network 上的这篇文章 - http://developer.yahoo.com/python/python-caching.html - 描述了如何将通过 urllib 进行的 http 调用缓存到内存或磁盘。

Answer 7

@dbr：您可能还需要添加 https 响应缓存：

def https_response(self, request, response):
    return self.http_response(request,response)