python标准库之urllib, httplib, urllib2

urllib.urlencode()

urllib2.urlopen()

urlib2学习指南：

查看源码可知是这样的路线。

数据流向

urllib2.urlopen() ->opener.open() -> Request() -> _open() -> 等等 -> httplib库

由此大致可以得出，要访问一个网址，可以使用如下几种方法。

urlopen()

opener.open()

Request()之后使用urlopen或者operner.open()

也就是说Request()这个类不提供open的操作，只是对数据的封装。

class Request:    def __init__(self, url, data=None, headers={},                 origin_req_host=None, unverifiable=False):        # unwrap('<URL:type://host/path>') --> 'type://host/path'        self.__original = unwrap(url)        self.__original, self.__fragment = splittag(self.__original)        self.type = None        # self.__r_type is what's left after doing the splittype        self.host = None        self.port = None        self._tunnel_host = None        self.data = data        self.headers = {}        for key, value in headers.items():            self.add_header(key, value)        self.unredirected_hdrs = {}        if origin_req_host is None:            origin_req_host = request_host(self)        self.origin_req_host = origin_req_host        self.unverifiable = unverifiable    def __getattr__(self, attr):        # XXX this is a fallback mechanism to guard against these        # methods getting called in a non-standard order.  this may be        # too complicated and/or unnecessary.        # XXX should the __r_XXX attributes be public?        if attr[:12] == '_Request__r_':            name = attr[12:]            if hasattr(Request, 'get_' + name):                getattr(self, 'get_' + name)()                return getattr(self, attr)        raise AttributeError, attr    def get_method(self):        if self.has_data():            return "POST"        else:            return "GET"    # XXX these helper methods are lame    def add_data(self, data):        self.data = data    def has_data(self):        return self.data is not None    def get_data(self):        return self.data    def get_full_url(self):        if self.__fragment:            return '%s#%s' % (self.__original, self.__fragment)        else:            return self.__original    def get_type(self):        if self.type is None:            self.type, self.__r_type = splittype(self.__original)            if self.type is None:                raise ValueError, "unknown url type: %s" % self.__original        return self.type    def get_host(self):        if self.host is None:            self.host, self.__r_host = splithost(self.__r_type)            if self.host:                self.host = unquote(self.host)        return self.host    def get_selector(self):        return self.__r_host    def set_proxy(self, host, type):        if self.type == 'https' and not self._tunnel_host:            self._tunnel_host = self.host        else:            self.type = type            self.__r_host = self.__original        self.host = host    def has_proxy(self):        return self.__r_host == self.__original    def get_origin_req_host(self):        return self.origin_req_host    def is_unverifiable(self):        return self.unverifiable    def add_header(self, key, val):        # useful for something like authentication        self.headers[key.capitalize()] = val    def add_unredirected_header(self, key, val):        # will not be added to a redirected request        self.unredirected_hdrs[key.capitalize()] = val    def has_header(self, header_name):        return (header_name in self.headers or                header_name in self.unredirected_hdrs)    def get_header(self, header_name, default=None):        return self.headers.get(            header_name,            self.unredirected_hdrs.get(header_name, default))    def header_items(self):        hdrs = self.unredirected_hdrs.copy()        hdrs.update(self.headers)        return hdrs.items()

opener是OpenDirector()的实例。

可以通过build_opener()函数， 也可以通过OpenerDirector实例化一个opener,然后调用add_handler方法。正所谓条条大道通罗马。

install_opener()可以让opener对urlopen()也生效

def install_opener(opener):    global _opener    _opener = opener

global语句被用来声明xxx是全局的——因此，当我们在函数内把值赋给xxx的时候，这个变化也反映在我们在主块中使用x的值的时候

def urlopen(url, data=None, timeout=socket._GLOBAL_DEFAULT_TIMEOUT,            cafile=None, capath=None, cadefault=False, context=None):    global _opener

    something