使用urllib2时，是否有一种简便的方法来缓存我所忽略的内容，还是我必须自己滚动？

解决方案

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

如果我们不介意以较低的级别工作，则httplib2(https://github.com/httplib2/httplib2)是一个出色的HTTP库，其中包含缓存功能。

我们可以使用装饰器函数，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函数：

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

这是假设我们不关注HTTP缓存控件，而只是想在应用程序期间缓存页面

我在寻找类似的东西，并遇到了danivo发布的"食谱491261：urllib2的缓存和限制"。问题是我真的不喜欢缓存代码(很多重复，很多手动连接文件路径而不是使用os.path.join，使用静态方法，非非常PEP8'sih以及我尝试避免的其他方式)

该代码稍微好一点(无论如何，以我的观点)，并且在功能上几乎是相同的，只是增加了一些主要是" recache"方法(示例用法可以在这里看到，或者在"如果__name__ ==" main"中出现：)。代码末尾的部分)。

最新版本可以在http://github.com/dbr/tvdb_api/blob/master/cache.py中找到，我将在此处粘贴以方便后代使用(已删除我的应用程序专用标头)：

#!/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()

Yahoo开发人员网络上的这篇文章http://developer.yahoo.com/python/python-caching.html描述了如何将通过urllib发出的http调用缓存到内存或者磁盘。

我一直在使用httplib2(它在处理HTTP缓存和身份验证方面做得很出色)与urllib2(在stdlib中，具有可扩展的接口并支持HTTP代理服务器)之间陷入困境。

ActiveState配方开始向urllib2添加缓存支持，但仅以非常原始的方式。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。它还不支持HTTP缓存头。

为了将httplib2缓存的最佳功能和urllib2的可扩展性结合在一起，我对ActiveState配方进行了修改，以实现与httplib2相同的大多数缓存功能。该模块位于jaraco.net中，名称为jaraco.net.http.caching。该链接指向撰写本文时所存在的模块。虽然该模块当前是较大的jaraco.net程序包的一部分，但它不具有程序包内依赖性，因此请随时将其拉出并在我们自己的项目中使用。

另外，如果我们具有Python 2.6或者更高版本，则可以" easy_install jaraco.net> = 1.3"，然后将CachingHandler与" caching.quick_test()"中的代码一起使用。

"""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没有提供有关缓存的后备存储的规范，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。同样，为Cachelib设计的其他为httplib2设计的后备缓存也应可用。

@dbr：我们可能还需要添加带有以下内容的https响应缓存：

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