# `urllib.request` --- 用于打开 URL 的可扩展库

源码： Lib/urllib/request.py

`urllib.request` 模块定义了适用于在各种复杂情况下打开 URL（主要为 HTTP）的函数和类 --- 例如基本认证、摘要认证、重定向、cookies 及其它。

参见

The Requests package is recommended for a higher-level HTTP client interface.

`urllib.request` 模块定义了以下函数：

`urllib.request.``urlopen`(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)

  打开统一资源定位地址 url，可以是一个字符串或一个 `Request` 对象。

  data must be an object specifying additional data to be sent to the server, or `None` if no such data is needed. See `Request` for details.

  urllib.request 模块使用 HTTP/1.1 并且在其 HTTP 请求中包含 `Connection:close` 头。

  The optional timeout parameter specifies a timeout in seconds for blocking operations like the connection attempt (if not specified, the global default timeout setting will be used). This actually only works for HTTP, HTTPS and FTP connections.

  If context is specified, it must be a `ssl.SSLContext` instance describing the various SSL options. See `HTTPSConnection` for more details.

  The optional cafile and capath parameters specify a set of trusted CA certificates for HTTPS requests. cafile should point to a single file containing a bundle of CA certificates, whereas capath should point to a directory of hashed certificate files. More information can be found in `ssl.SSLContext.load_verify_locations()`.

  The cadefault parameter is ignored.

  This function always returns an object which can work as a context manager and has methods such as

  - `geturl()` --- return the URL of the resource retrieved, commonly used to determine if a redirect was followed

  - `info()` --- return the meta-information of the page, such as headers, in the form of an `email.message_from_string()` instance (see Quick Reference to HTTP Headers)

  - `getcode()` -- return the HTTP status code of the response.

  For HTTP and HTTPS URLs, this function returns a `http.client.HTTPResponse` object slightly modified. In addition to the three new methods above, the msg attribute contains the same information as the `reason` attribute --- the reason phrase returned by server --- instead of the response headers as it is specified in the documentation for `HTTPResponse`.

  For FTP, file, and data URLs and requests explicitly handled by legacy `URLopener` and `FancyURLopener` classes, this function returns a `urllib.response.addinfourl` object.

  协议错误时引发 `URLError`。

  Note that `None` may be returned if no handler handles the request (though the default installed global `OpenerDirector` uses `UnknownHandler` to ensure this never happens).

  In addition, if proxy settings are detected (for example, when a `*_proxy` environment variable like `http_proxy` is set), `ProxyHandler` is default installed and makes sure the requests are handled through the proxy.

  The legacy `urllib.urlopen` function from Python 2.6 and earlier has been discontinued; `urllib.request.urlopen()` corresponds to the old `urllib2.urlopen`. Proxy handling, which was done by passing a dictionary parameter to `urllib.urlopen`, can be obtained by using `ProxyHandler` objects.

  The default opener raises an auditing event `urllib.Request` with arguments `fullurl`, `data`, `headers`, `method` taken from the request object.

  在 3.2 版更改: 增加了 cafile 与 capath。

  在 3.2 版更改: 现在如果可行（指 `ssl.HAS_SNI` 为真），支持 HTTPS 虚拟主机

  3.2 新版功能: data 可以是一个可迭代对象。

  在 3.3 版更改: 增加了 cadefault。

  在 3.4.3 版更改: 增加了 context。

  3.6 版后已移除: cafile, capath and cadefault are deprecated in favor of context. Please use `ssl.SSLContext.load_cert_chain()` instead, or let `ssl.create_default_context()` select the system's trusted CA certificates for you.

`urllib.request.``install_opener`(opener)

  Install an `OpenerDirector` instance as the default global opener. Installing an opener is only necessary if you want urlopen to use that opener; otherwise, simply call `OpenerDirector.open()` instead of `urlopen()`. The code does not check for a real `OpenerDirector`, and any class with the appropriate interface will work.

`urllib.request.``build_opener`([handler, ...])

  Return an `OpenerDirector` instance, which chains the handlers in the order given. handlers can be either instances of `BaseHandler`, or subclasses of `BaseHandler` (in which case it must be possible to call the constructor without any parameters). Instances of the following classes will be in front of the handlers, unless the handlers contain them, instances of them or subclasses of them: `ProxyHandler` (if proxy settings are detected), `UnknownHandler`, `HTTPHandler`, `HTTPDefaultErrorHandler`, `HTTPRedirectHandler`, `FTPHandler`, `FileHandler`, `HTTPErrorProcessor`.

  若 Python 安装有 SLL 支持（指可以导入 `ssl` 模块），亦会加入 `HTTPSHandler`。

  A `BaseHandler` subclass may also change its `handler_order` attribute to modify its position in the handlers list.

`urllib.request.``pathname2url`(path)

  Convert the pathname path from the local syntax for a path to the form used in the path component of a URL. This does not produce a complete URL. The return value will already be quoted using the `quote()` function.

`urllib.request.``url2pathname`(path)

  Convert the path component path from a percent-encoded URL to the local syntax for a path. This does not accept a complete URL. This function uses `unquote()` to decode path.

`urllib.request.``getproxies`()

  This helper function returns a dictionary of scheme to proxy server URL mappings. It scans the environment for variables named `<scheme>_proxy`, in a case insensitive approach, for all operating systems first, and when it cannot find it, looks for proxy information from Mac OSX System Configuration for Mac OS X and Windows Systems Registry for Windows. If both lowercase and uppercase environment variables exist (and disagree), lowercase is preferred.

  注解

  If the environment variable `REQUEST_METHOD` is set, which usually indicates your script is running in a CGI environment, the environment variable `HTTP_PROXY` (uppercase `_PROXY`) will be ignored. This is because that variable can be injected by a client using the "Proxy:" HTTP header. If you need to use an HTTP proxy in a CGI environment, either use `ProxyHandler` explicitly, or make sure the variable name is in lowercase (or at least the `_proxy` suffix).

提供了以下类：

class `urllib.request.``Request`(url, data=None, headers={}, origin_req_host=None, unverifiable=False, method=None)

  This class is an abstraction of a URL request.

  url 应是一个含有一个有效 URL 的字符串。

  data must be an object specifying additional data to send to the server, or `None` if no such data is needed. Currently HTTP requests are the only ones that use data. The supported object types include bytes, file-like objects, and iterables of bytes-like objects. If no `Content-Length` nor `Transfer-Encoding` header field has been provided, `HTTPHandler` will set these headers according to the type of data. `Content-Length` will be used to send bytes objects, while `Transfer-Encoding: chunked` as specified in RFC 7230, Section 3.3.1 will be used to send files and other iterables.

  For an HTTP POST request method, data should be a buffer in the standard application/x-www-form-urlencoded format. The `urllib.parse.urlencode()` function takes a mapping or sequence of 2-tuples and returns an ASCII string in this format. It should be encoded to bytes before being used as the data parameter.

  headers should be a dictionary, and will be treated as if `add_header()` was called with each key and value as arguments. This is often used to "spoof" the `User-Agent` header value, which is used by a browser to identify itself -- some HTTP servers only allow requests coming from common browsers as opposed to scripts. For example, Mozilla Firefox may identify itself as `"Mozilla/5.0 (X11; U; Linux i686) Gecko/20071127 Firefox/2.0.0.11"`, while `urllib`'s default user agent string is `"Python-urllib/2.6"` (on Python 2.6).

  An appropriate `Content-Type` header should be included if the data argument is present. If this header has not been provided and data is not None, `Content-Type: application/x-www-form-urlencoded` will be added as a default.

  The next two arguments are only of interest for correct handling of third-party HTTP cookies:

  origin_req_host should be the request-host of the origin transaction, as defined by RFC 2965. It defaults to `http.cookiejar.request_host(self)`. This is the host name or IP address of the original request that was initiated by the user. For example, if the request is for an image in an HTML document, this should be the request-host of the request for the page containing the image.

  unverifiable should indicate whether the request is unverifiable, as defined by RFC 2965. It defaults to `False`. An unverifiable request is one whose URL the user did not have the option to approve. For example, if the request is for an image in an HTML document, and the user had no option to approve the automatic fetching of the image, this should be true.

  method should be a string that indicates the HTTP request method that will be used (e.g. `'HEAD'`). If provided, its value is stored in the `method` attribute and is used by `get_method()`. The default is `'GET'` if data is `None` or `'POST'` otherwise. Subclasses may indicate a different default method by setting the `method` attribute in the class itself.

  注解

  The request will not work as expected if the data object is unable to deliver its content more than once (e.g. a file or an iterable that can produce the content only once) and the request is retried for HTTP redirects or authentication. The data is sent to the HTTP server right away after the headers. There is no support for a 100-continue expectation in the library.

  在 3.3 版更改: Request 类增加了 `Request.method` 参数。

  在 3.4 版更改: Default `Request.method` may be indicated at the class level.

  在 3.6 版更改: Do not raise an error if the `Content-Length` has not been provided and data is neither `None` nor a bytes object. Fall back to use chunked transfer encoding instead.

class `urllib.request.``OpenerDirector`

  The `OpenerDirector` class opens URLs via `BaseHandler`s chained together. It manages the chaining of handlers, and recovery from errors.

class `urllib.request.``BaseHandler`

  This is the base class for all registered handlers --- and handles only the simple mechanics of registration.

class `urllib.request.``HTTPDefaultErrorHandler`

  A class which defines a default handler for HTTP error responses; all responses are turned into `HTTPError` exceptions.

class `urllib.request.``HTTPRedirectHandler`

  一个用于处理重定向的类。

class `urllib.request.``HTTPCookieProcessor`(cookiejar=None)

  一个用于处理 HTTP Cookies 的类。

class `urllib.request.``ProxyHandler`(proxies=None)

  Cause requests to go through a proxy. If proxies is given, it must be a dictionary mapping protocol names to URLs of proxies. The default is to read the list of proxies from the environment variables `<protocol>_proxy`. If no proxy environment variables are set, then in a Windows environment proxy settings are obtained from the registry's Internet Settings section, and in a Mac OS X environment proxy information is retrieved from the OS X System Configuration Framework.

  To disable autodetected proxy pass an empty dictionary.

  The `no_proxy` environment variable can be used to specify hosts which shouldn't be reached via proxy; if set, it should be a comma-separated list of hostname suffixes, optionally with `:port` appended, for example `cern.ch,ncsa.uiuc.edu,some.host:8080`.

  > 注解

  > `HTTP_PROXY` will be ignored if a variable `REQUEST_METHOD` is set; see the documentation on `getproxies()`.

class `urllib.request.``HTTPPasswordMgr`

  Keep a database of `(realm, uri) -> (user, password)` mappings.

class `urllib.request.``HTTPPasswordMgrWithDefaultRealm`

  Keep a database of `(realm, uri) -> (user, password)` mappings. A realm of `None` is considered a catch-all realm, which is searched if no other realm fits.

class `urllib.request.``HTTPPasswordMgrWithPriorAuth`

  A variant of `HTTPPasswordMgrWithDefaultRealm` that also has a database of `uri -> is_authenticated` mappings. Can be used by a BasicAuth handler to determine when to send authentication credentials immediately instead of waiting for a `401` response first.

  3.5 新版功能.

class `urllib.request.``AbstractBasicAuthHandler`(password_mgr=None)

  This is a mixin class that helps with HTTP authentication, both to the remote host and to a proxy. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported. If passwd_mgr also provides `is_authenticated` and `update_authenticated` methods (see HTTPPasswordMgrWithPriorAuth 对象), then the handler will use the `is_authenticated` result for a given URI to determine whether or not to send authentication credentials with the request. If `is_authenticated` returns `True` for the URI, credentials are sent. If `is_authenticated` is `False`, credentials are not sent, and then if a `401` response is received the request is re-sent with the authentication credentials. If authentication succeeds, `update_authenticated` is called to set `is_authenticated` `True` for the URI, so that subsequent requests to the URI or any of its super-URIs will automatically include the authentication credentials.

  3.5 新版功能: 增加了对 `is_authenticated` 的支持。

class `urllib.request.``HTTPBasicAuthHandler`(password_mgr=None)

  Handle authentication with the remote host. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported. HTTPBasicAuthHandler will raise a `ValueError` when presented with a wrong Authentication scheme.

class `urllib.request.``ProxyBasicAuthHandler`(password_mgr=None)

  Handle authentication with the proxy. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported.

class `urllib.request.``AbstractDigestAuthHandler`(password_mgr=None)

  This is a mixin class that helps with HTTP authentication, both to the remote host and to a proxy. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported.

class `urllib.request.``HTTPDigestAuthHandler`(password_mgr=None)

  Handle authentication with the remote host. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported. When both Digest Authentication Handler and Basic Authentication Handler are both added, Digest Authentication is always tried first. If the Digest Authentication returns a 40x response again, it is sent to Basic Authentication handler to Handle. This Handler method will raise a `ValueError` when presented with an authentication scheme other than Digest or Basic.

  在 3.3 版更改: Raise `ValueError` on unsupported Authentication Scheme.

class `urllib.request.``ProxyDigestAuthHandler`(password_mgr=None)

  Handle authentication with the proxy. password_mgr, if given, should be something that is compatible with `HTTPPasswordMgr`; refer to section HTTPPasswordMgr 对象 for information on the interface that must be supported.

class `urllib.request.``HTTPHandler`

  A class to handle opening of HTTP URLs.

class `urllib.request.``HTTPSHandler`(debuglevel=0, context=None, check_hostname=None)

  A class to handle opening of HTTPS URLs. context and check_hostname have the same meaning as in `http.client.HTTPSConnection`.

  在 3.2 版更改: context and check_hostname were added.

class `urllib.request.``FileHandler`

  打开本地文件。

class `urllib.request.``DataHandler`

  Open data URLs.

  3.4 新版功能.

class `urllib.request.``FTPHandler`

  打开 FTP URLs。

class `urllib.request.``CacheFTPHandler`

  Open FTP URLs, keeping a cache of open FTP connections to minimize delays.

class `urllib.request.``UnknownHandler`

  A catch-all class to handle unknown URLs.

class `urllib.request.``HTTPErrorProcessor`

  Process HTTP error responses.

## Request 对象

The following methods describe `Request`'s public interface, and so all may be overridden in subclasses. It also defines several public attributes that can be used by clients to inspect the parsed request.

`Request.``full_url`

  传给构造函数的原始 URL。

  在 3.4 版更改.

  Request.full_url is a property with setter, getter and a deleter. Getting `full_url` returns the original request URL with the fragment, if it was present.

`Request.``type`

  The URI scheme.

`Request.``host`

  The URI authority, typically a host, but may also contain a port separated by a colon.

`Request.``origin_req_host`

  请求的原始主机，不含端口。

`Request.``selector`

  URI 路径。若 `Request` 使用代理，选择器将会是传给代理的完整 URL。

`Request.``data`

  The entity body for the request, or `None` if not specified.

  在 3.4 版更改: Changing value of `Request.data` now deletes "Content-Length" header if it was previously set or calculated.

`Request.``unverifiable`

  布尔，表明请求是否为 RFC 2965 中定义的无法证实的。

`Request.``method`

  The HTTP request method to use. By default its value is `None`, which means that `get_method()` will do its normal computation of the method to be used. Its value can be set (thus overriding the default computation in `get_method()`) either by providing a default value by setting it at the class level in a `Request` subclass, or by passing a value in to the `Request` constructor via the method argument.

  3.3 新版功能.

  在 3.4 版更改: A default value can now be set in subclasses; previously it could only be set via the constructor argument.

`Request.``get_method`()

  Return a string indicating the HTTP request method. If `Request.method` is not `None`, return its value, otherwise return `'GET'` if `Request.data` is `None`, or `'POST'` if it's not. This is only meaningful for HTTP requests.

  在 3.3 版更改: get_method now looks at the value of `Request.method`.

`Request.``add_header`(key, val)

  Add another header to the request. Headers are currently ignored by all handlers except HTTP handlers, where they are added to the list of headers sent to the server. Note that there cannot be more than one header with the same name, and later calls will overwrite previous calls in case the key collides. Currently, this is no loss of HTTP functionality, since all headers which have meaning when used more than once have a (header-specific) way of gaining the same functionality using only one header.

`Request.``add_unredirected_header`(key, header)

  添加一个不会被加入重定向请求的头部。

`Request.``has_header`(header)

  Return whether the instance has the named header (checks both regular and unredirected).

`Request.``remove_header`(header)

  Remove named header from the request instance (both from regular and unredirected headers).

  3.4 新版功能.

`Request.``get_full_url`()

  返回构造器中给定的 URL。

  在 3.4 版更改.

  返回 `Request.full_url`

`Request.``set_proxy`(host, type)

  Prepare the request by connecting to a proxy server. The host and type will replace those of the instance, and the instance's selector will be the original URL given in the constructor.

`Request.``get_header`(header_name, default=None)

  Return the value of the given header. If the header is not present, return the default value.

`Request.``header_items`()

  Return a list of tuples (header_name, header_value) of the Request headers.

在 3.4 版更改: The request methods add_data, has_data, get_data, get_type, get_host, get_selector, get_origin_req_host and is_unverifiable that were deprecated since 3.3 have been removed.

## OpenerDirector 对象

`OpenerDirector` 实例有以下方法：

`OpenerDirector.``add_handler`(handler)

  handler should be an instance of `BaseHandler`. The following methods are searched, and added to the possible chains (note that HTTP errors are a special case). Note that, in the following, protocol should be replaced with the actual protocol to handle, for example `http_response()` would be the HTTP protocol response handler. Also type should be replaced with the actual HTTP code, for example `http_error_404()` would handle HTTP 404 errors.

  - `<protocol>_open()` — 句柄知道如何打开 protocol URLs 的信号。

    查看 `BaseHandler.<protocol>_open()` 以获取更多信息。

  - `http_error_<type>()` --- signal that the handler knows how to handle HTTP errors with HTTP error code type.

    查看 `BaseHandler.http_error_<nnn>()` 以获取更多信息。

  - `<protocol>_error()` — 句柄知道如何处理来自（非-`http`）*protocol* 的错误的信号。

  - `<protocol>_request()` — 句柄知道如何预处理 protocol 请求的信号。

    查看 `BaseHandler.<protocol>_request()` 以获取更多信息。

  - `<protocol>_response()` — 句柄知道如何后处理 protocol 响应的信号。

    查看 `BaseHandler.<protocol>_response()` 以获取更多信息。

`OpenerDirector.``open`(url, data=None[, timeout])

  Open the given url (which can be a request object or a string), optionally passing the given data. Arguments, return values and exceptions raised are the same as those of `urlopen()` (which simply calls the `open()` method on the currently installed global `OpenerDirector`). The optional timeout parameter specifies a timeout in seconds for blocking operations like the connection attempt (if not specified, the global default timeout setting will be used). The timeout feature actually works only for HTTP, HTTPS and FTP connections).

`OpenerDirector.``error`(proto, *args)

  Handle an error of the given protocol. This will call the registered error handlers for the given protocol with the given arguments (which are protocol specific). The HTTP protocol is a special case which uses the HTTP response code to determine the specific error handler; refer to the `http_error_<type>()` methods of the handler classes.

  Return values and exceptions raised are the same as those of `urlopen()`.

OpenerDirector objects open URLs in three stages:

The order in which these methods are called within each stage is determined by sorting the handler instances.

1. Every handler with a method named like `<protocol>_request()` has that method called to pre-process the request.

2. Handlers with a method named like `<protocol>_open()` are called to handle the request. This stage ends when a handler either returns a non-`None` value (ie. a response), or raises an exception (usually `URLError`). Exceptions are allowed to propagate.

   In fact, the above algorithm is first tried for methods named `default_open()`. If all such methods return `None`, the algorithm is repeated for methods named like `<protocol>_open()`. If all such methods return `None`, the algorithm is repeated for methods named `unknown_open()`.

   Note that the implementation of these methods may involve calls of the parent `OpenerDirector` instance's `open()` and `error()` methods.

3. Every handler with a method named like `<protocol>_response()` has that method called to post-process the response.

## BaseHandler 对象

`BaseHandler` objects provide a couple of methods that are directly useful, and others that are meant to be used by derived classes. These are intended for direct use:

`BaseHandler.``add_parent`(director)

  Add a director as parent.

`BaseHandler.``close`()

  Remove any parents.

The following attribute and methods should only be used by classes derived from `BaseHandler`.

注解

The convention has been adopted that subclasses defining `<protocol>_request()` or `<protocol>_response()` methods are named `*Processor`; all others are named `*Handler`.

`BaseHandler.``parent`

  A valid `OpenerDirector`, which can be used to open using a different protocol, or handle errors.

`BaseHandler.``default_open`(req)

  This method is not defined in `BaseHandler`, but subclasses should define it if they want to catch all URLs.

  This method, if implemented, will be called by the parent `OpenerDirector`. It should return a file-like object as described in the return value of the `open()` of `OpenerDirector`, or `None`. It should raise `URLError`, unless a truly exceptional thing happens (for example, `MemoryError` should not be mapped to `URLError`).

  This method will be called before any protocol-specific open method.

`BaseHandler.<protocol>_open(req)`

  This method is not defined in `BaseHandler`, but subclasses should define it if they want to handle URLs with the given protocol.

  This method, if defined, will be called by the parent `OpenerDirector`. Return values should be the same as for `default_open()`.

`BaseHandler.``unknown_open`(req)

  This method is not defined in `BaseHandler`, but subclasses should define it if they want to catch all URLs with no specific registered handler to open it.

  This method, if implemented, will be called by the `parent` `OpenerDirector`. Return values should be the same as for `default_open()`.

`BaseHandler.``http_error_default`(req, fp, code, msg, hdrs)

  This method is not defined in `BaseHandler`, but subclasses should override it if they intend to provide a catch-all for otherwise unhandled HTTP errors. It will be called automatically by the `OpenerDirector` getting the error, and should not normally be called in other circumstances.

  req will be a `Request` object, fp will be a file-like object with the HTTP error body, code will be the three-digit code of the error, msg will be the user-visible explanation of the code and hdrs will be a mapping object with the headers of the error.

  Return values and exceptions raised should be the same as those of `urlopen()`.

`BaseHandler.http_error_<nnn>(req, fp, code, msg, hdrs)`

  nnn should be a three-digit HTTP error code. This method is also not defined in `BaseHandler`, but will be called, if it exists, on an instance of a subclass, when an HTTP error with code nnn occurs.

  Subclasses should override this method to handle specific HTTP errors.

  Arguments, return values and exceptions raised should be the same as for `http_error_default()`.

`BaseHandler.<protocol>_request(req)`

  This method is not defined in `BaseHandler`, but subclasses should define it if they want to pre-process requests of the given protocol.

  This method, if defined, will be called by the parent `OpenerDirector`. req will be a `Request` object. The return value should be a `Request` object.

`BaseHandler.<protocol>_response(req, response)`

  This method is not defined in `BaseHandler`, but subclasses should define it if they want to post-process responses of the given protocol.

  This method, if defined, will be called by the parent `OpenerDirector`. req will be a `Request` object. response will be an object implementing the same interface as the return value of `urlopen()`. The return value should implement the same interface as the return value of `urlopen()`.

## HTTPRedirectHandler 对象

注解

Some HTTP redirections require action from this module's client code. If this is the case, `HTTPError` is raised. See RFC 2616 for details of the precise meanings of the various redirection codes.

An `HTTPError` exception raised as a security consideration if the HTTPRedirectHandler is presented with a redirected URL which is not an HTTP, HTTPS or FTP URL.

`HTTPRedirectHandler.``redirect_request`(req, fp, code, msg, hdrs, newurl)

  Return a `Request` or `None` in response to a redirect. This is called by the default implementations of the `http_error_30*()` methods when a redirection is received from the server. If a redirection should take place, return a new `Request` to allow `http_error_30*()` to perform the redirect to newurl. Otherwise, raise `HTTPError` if no other handler should try to handle this URL, or return `None` if you can't but another handler might.

  注解

  The default implementation of this method does not strictly follow RFC 2616, which says that 301 and 302 responses to `POST` requests must not be automatically redirected without confirmation by the user. In reality, browsers do allow automatic redirection of these responses, changing the POST to a `GET`, and the default implementation reproduces this behavior.

`HTTPRedirectHandler.``http_error_301`(req, fp, code, msg, hdrs)

  Redirect to the `Location:` or `URI:` URL. This method is called by the parent `OpenerDirector` when getting an HTTP 'moved permanently' response.

`HTTPRedirectHandler.``http_error_302`(req, fp, code, msg, hdrs)

  The same as `http_error_301()`, but called for the 'found' response.

`HTTPRedirectHandler.``http_error_303`(req, fp, code, msg, hdrs)

  The same as `http_error_301()`, but called for the 'see other' response.

`HTTPRedirectHandler.``http_error_307`(req, fp, code, msg, hdrs)

  The same as `http_error_301()`, but called for the 'temporary redirect' response.

## HTTPCookieProcessor 对象

`HTTPCookieProcessor` instances have one attribute:

`HTTPCookieProcessor.``cookiejar`

  The `http.cookiejar.CookieJar` in which cookies are stored.

## ProxyHandler 对象

`ProxyHandler.<protocol>_open(request)`

  The `ProxyHandler` will have a method `<protocol>_open()` for every protocol which has a proxy in the proxies dictionary given in the constructor. The method will modify requests to go through the proxy, by calling `request.set_proxy()`, and call the next handler in the chain to actually execute the protocol.

## HTTPPasswordMgr 对象

These methods are available on `HTTPPasswordMgr` and `HTTPPasswordMgrWithDefaultRealm` objects.

`HTTPPasswordMgr.``add_password`(realm, uri, user, passwd)

  uri can be either a single URI, or a sequence of URIs. realm, user and passwd must be strings. This causes `(user, passwd)` to be used as authentication tokens when authentication for realm and a super-URI of any of the given URIs is given.

`HTTPPasswordMgr.``find_user_password`(realm, authuri)

  Get user/password for given realm and URI, if any. This method will return `(None, None)` if there is no matching user/password.

  For `HTTPPasswordMgrWithDefaultRealm` objects, the realm `None` will be searched if the given realm has no matching user/password.

## HTTPPasswordMgrWithPriorAuth 对象

This password manager extends `HTTPPasswordMgrWithDefaultRealm` to support tracking URIs for which authentication credentials should always be sent.

`HTTPPasswordMgrWithPriorAuth.``add_password`(realm, uri, user, passwd, is_authenticated=False)

  realm, uri, user, passwd are as for `HTTPPasswordMgr.add_password()`. is_authenticated sets the initial value of the `is_authenticated` flag for the given URI or list of URIs. If is_authenticated is specified as `True`, realm is ignored.

`HTTPPasswordMgrWithPriorAuth.``find_user_password`(realm, authuri)

  Same as for `HTTPPasswordMgrWithDefaultRealm` objects

`HTTPPasswordMgrWithPriorAuth.``update_authenticated`(self, uri, is_authenticated=False)

  Update the `is_authenticated` flag for the given uri or list of URIs.

`HTTPPasswordMgrWithPriorAuth.``is_authenticated`(self, authuri)

  Returns the current state of the `is_authenticated` flag for the given URI.

## AbstractBasicAuthHandler 对象

`AbstractBasicAuthHandler.``http_error_auth_reqed`(authreq, host, req, headers)

  Handle an authentication request by getting a user/password pair, and re-trying the request. authreq should be the name of the header where the information about the realm is included in the request, host specifies the URL and path to authenticate for, req should be the (failed) `Request` object, and headers should be the error headers.

  host is either an authority (e.g. `"python.org"`) or a URL containing an authority component (e.g. `"http://python.org/"`). In either case, the authority must not contain a userinfo component (so, `"python.org"` and `"python.org:80"` are fine, `"joe:password@python.org"` is not).

## HTTPBasicAuthHandler 对象

`HTTPBasicAuthHandler.``http_error_401`(req, fp, code, msg, hdrs)

  Retry the request with authentication information, if available.

## ProxyBasicAuthHandler 对象

`ProxyBasicAuthHandler.``http_error_407`(req, fp, code, msg, hdrs)

  Retry the request with authentication information, if available.

## AbstractDigestAuthHandler 对象

`AbstractDigestAuthHandler.``http_error_auth_reqed`(authreq, host, req, headers)

  authreq should be the name of the header where the information about the realm is included in the request, host should be the host to authenticate to, req should be the (failed) `Request` object, and headers should be the error headers.

## HTTPDigestAuthHandler 对象

`HTTPDigestAuthHandler.``http_error_401`(req, fp, code, msg, hdrs)

  Retry the request with authentication information, if available.

## ProxyDigestAuthHandler 对象

`ProxyDigestAuthHandler.``http_error_407`(req, fp, code, msg, hdrs)

  Retry the request with authentication information, if available.

## HTTPHandler 对象

`HTTPHandler.``http_open`(req)

  Send an HTTP request, which can be either GET or POST, depending on `req.has_data()`.

## HTTPSHandler 对象

`HTTPSHandler.``https_open`(req)

  Send an HTTPS request, which can be either GET or POST, depending on `req.has_data()`.

## FileHandler 对象

`FileHandler.``file_open`(req)

  Open the file locally, if there is no host name, or the host name is `'localhost'`.

  在 3.2 版更改: This method is applicable only for local hostnames. When a remote hostname is given, an `URLError` is raised.

## DataHandler 对象

`DataHandler.``data_open`(req)

  Read a data URL. This kind of URL contains the content encoded in the URL itself. The data URL syntax is specified in RFC 2397. This implementation ignores white spaces in base64 encoded data URLs so the URL may be wrapped in whatever source file it comes from. But even though some browsers don't mind about a missing padding at the end of a base64 encoded data URL, this implementation will raise an `ValueError` in that case.

## FTPHandler 对象

`FTPHandler.``ftp_open`(req)

  Open the FTP file indicated by req. The login is always done with empty username and password.

## CacheFTPHandler 对象

`CacheFTPHandler` objects are `FTPHandler` objects with the following additional methods:

`CacheFTPHandler.``setTimeout`(t)

  Set timeout of connections to t seconds.

`CacheFTPHandler.``setMaxConns`(m)

  Set maximum number of cached connections to m.

## UnknownHandler 对象

`UnknownHandler.``unknown_open`()

  Raise a `URLError` exception.

## HTTPErrorProcessor 对象

`HTTPErrorProcessor.``http_response`(request, response)

  Process HTTP error responses.

  For 200 error codes, the response object is returned immediately.

  For non-200 error codes, this simply passes the job on to the `http_error_<type>()` handler methods, via `OpenerDirector.error()`. Eventually, `HTTPDefaultErrorHandler` will raise an `HTTPError` if no other handler handles the error.

`HTTPErrorProcessor.``https_response`(request, response)

  Process HTTPS error responses.

  The behavior is same as `http_response()`.

## 例子

In addition to the examples below, more examples are given in HOWTO 使用 urllib 包获取网络资源.

This example gets the python.org main page and displays the first 300 bytes of it.

    >>> import urllib.request
    >>> with urllib.request.urlopen('http://www.python.org/') as f:
    ...     print(f.read(300))
    ...
    b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\n\n\n<html
    xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">\n\n<head>\n
    <meta http-equiv="content-type" content="text/html; charset=utf-8" />\n
    <title>Python Programming '

Note that urlopen returns a bytes object. This is because there is no way for urlopen to automatically determine the encoding of the byte stream it receives from the HTTP server. In general, a program will decode the returned bytes object to string once it determines or guesses the appropriate encoding.

The following W3C document, https://www.w3.org/International/O-charset, lists the various ways in which an (X)HTML or an XML document could have specified its encoding information.

As the python.org website uses utf-8 encoding as specified in its meta tag, we will use the same for decoding the bytes object.

    >>> with urllib.request.urlopen('http://www.python.org/') as f:
    ...     print(f.read(100).decode('utf-8'))
    ...
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtm

It is also possible to achieve the same result without using the context manager approach.

    >>> import urllib.request
    >>> f = urllib.request.urlopen('http://www.python.org/')
    >>> print(f.read(100).decode('utf-8'))
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtm

In the following example, we are sending a data-stream to the stdin of a CGI and reading the data it returns to us. Note that this example will only work when the Python installation supports SSL.

    >>> import urllib.request
    >>> req = urllib.request.Request(url='https://localhost/cgi-bin/test.cgi',
    ...                       data=b'This data is passed to stdin of the CGI')
    >>> with urllib.request.urlopen(req) as f:
    ...     print(f.read().decode('utf-8'))
    ...
    Got Data: "This data is passed to stdin of the CGI"

The code for the sample CGI used in the above example is:

    #!/usr/bin/env python
    import sys
    data = sys.stdin.read()
    print('Content-type: text/plain\n\nGot Data: "%s"' % data)

Here is an example of doing a `PUT` request using `Request`:

    import urllib.request
    DATA = b'some data'
    req = urllib.request.Request(url='http://localhost:8080', data=DATA,method='PUT')
    with urllib.request.urlopen(req) as f:
        pass
    print(f.status)
    print(f.reason)

Use of Basic HTTP Authentication:

    import urllib.request
    # Create an OpenerDirector with support for Basic HTTP Authentication...
    auth_handler = urllib.request.HTTPBasicAuthHandler()
    auth_handler.add_password(realm='PDQ Application',
                              uri='https://mahler:8092/site-updates.py',
                              user='klem',
                              passwd='kadidd!ehopper')
    opener = urllib.request.build_opener(auth_handler)
    # ...and install it globally so it can be used with urlopen.
    urllib.request.install_opener(opener)
    urllib.request.urlopen('http://www.example.com/login.html')

`build_opener()` provides many handlers by default, including a `ProxyHandler`. By default, `ProxyHandler` uses the environment variables named `<scheme>_proxy`, where `<scheme>` is the URL scheme involved. For example, the `http_proxy` environment variable is read to obtain the HTTP proxy's URL.

This example replaces the default `ProxyHandler` with one that uses programmatically-supplied proxy URLs, and adds proxy authorization support with `ProxyBasicAuthHandler`.

    proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
    proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
    proxy_auth_handler.add_password('realm', 'host', 'username', 'password')

    opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
    # This time, rather than install the OpenerDirector, we use it directly:
    opener.open('http://www.example.com/login.html')

Adding HTTP headers:

Use the headers argument to the `Request` constructor, or:

    import urllib.request
    req = urllib.request.Request('http://www.example.com/')
    req.add_header('Referer', 'http://www.python.org/')
    # Customize the default User-Agent header value:
    req.add_header('User-Agent', 'urllib-example/0.1 (Contact: . . .)')
    r = urllib.request.urlopen(req)

`OpenerDirector` automatically adds a User-Agent header to every `Request`. To change this:

    import urllib.request
    opener = urllib.request.build_opener()
    opener.addheaders = [('User-agent', 'Mozilla/5.0')]
    opener.open('http://www.example.com/')

Also, remember that a few standard headers (Content-Length, Content-Type and Host) are added when the `Request` is passed to `urlopen()` (or `OpenerDirector.open()`).

Here is an example session that uses the `GET` method to retrieve a URL containing parameters:

    >>> import urllib.request
    >>> import urllib.parse
    >>> params = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
    >>> url = "http://www.musi-cal.com/cgi-bin/query?%s" % params
    >>> with urllib.request.urlopen(url) as f:
    ...     print(f.read().decode('utf-8'))
    ...

The following example uses the `POST` method instead. Note that params output from urlencode is encoded to bytes before it is sent to urlopen as data:

    >>> import urllib.request
    >>> import urllib.parse
    >>> data = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
    >>> data = data.encode('ascii')
    >>> with urllib.request.urlopen("http://requestb.in/xrbl82xr", data) as f:
    ...     print(f.read().decode('utf-8'))
    ...

The following example uses an explicitly specified HTTP proxy, overriding environment settings:

    >>> import urllib.request
    >>> proxies = {'http': 'http://proxy.example.com:8080/'}
    >>> opener = urllib.request.FancyURLopener(proxies)
    >>> with opener.open("http://www.python.org") as f:
    ...     f.read().decode('utf-8')
    ...

The following example uses no proxies at all, overriding environment settings:

    >>> import urllib.request
    >>> opener = urllib.request.FancyURLopener({})
    >>> with opener.open("http://www.python.org/") as f:
    ...     f.read().decode('utf-8')
    ...

## Legacy interface

The following functions and classes are ported from the Python 2 module `urllib` (as opposed to `urllib2`). They might become deprecated at some point in the future.

`urllib.request.``urlretrieve`(url, filename=None, reporthook=None, data=None)

  Copy a network object denoted by a URL to a local file. If the URL points to a local file, the object will not be copied unless filename is supplied. Return a tuple `(filename, headers)` where filename is the local file name under which the object can be found, and headers is whatever the `info()` method of the object returned by `urlopen()` returned (for a remote object). Exceptions are the same as for `urlopen()`.

  The second argument, if present, specifies the file location to copy to (if absent, the location will be a tempfile with a generated name). The third argument, if present, is a callable that will be called once on establishment of the network connection and once after each block read thereafter. The callable will be passed three arguments; a count of blocks transferred so far, a block size in bytes, and the total size of the file. The third argument may be `-1` on older FTP servers which do not return a file size in response to a retrieval request.

  The following example illustrates the most common usage scenario:

      >>> import urllib.request
      >>> local_filename, headers = urllib.request.urlretrieve('http://python.org/')
      >>> html = open(local_filename)
      >>> html.close()

  If the url uses the `http:` scheme identifier, the optional data argument may be given to specify a `POST` request (normally the request type is `GET`). The data argument must be a bytes object in standard application/x-www-form-urlencoded format; see the `urllib.parse.urlencode()` function.

  `urlretrieve()` will raise `ContentTooShortError` when it detects that the amount of data available was less than the expected amount (which is the size reported by a Content-Length header). This can occur, for example, when the download is interrupted.

  The Content-Length is treated as a lower bound: if there's more data to read, urlretrieve reads more data, but if less data is available, it raises the exception.

  You can still retrieve the downloaded data in this case, it is stored in the `content` attribute of the exception instance.

  If no Content-Length header was supplied, urlretrieve can not check the size of the data it has downloaded, and just returns it. In this case you just have to assume that the download was successful.

`urllib.request.``urlcleanup`()

  Cleans up temporary files that may have been left behind by previous calls to `urlretrieve()`.

class `urllib.request.``URLopener`(proxies=None, **x509)

  3.3 版后已移除.

  Base class for opening and reading URLs. Unless you need to support opening objects using schemes other than `http:`, `ftp:`, or `file:`, you probably want to use `FancyURLopener`.

  By default, the `URLopener` class sends a User-Agent header of `urllib/VVV`, where VVV is the `urllib` version number. Applications can define their own User-Agent header by subclassing `URLopener` or `FancyURLopener` and setting the class attribute `version` to an appropriate string value in the subclass definition.

  The optional proxies parameter should be a dictionary mapping scheme names to proxy URLs, where an empty dictionary turns proxies off completely. Its default value is `None`, in which case environmental proxy settings will be used if present, as discussed in the definition of `urlopen()`, above.

  Additional keyword parameters, collected in x509, may be used for authentication of the client when using the `https:` scheme. The keywords key_file and cert_file are supported to provide an SSL key and certificate; both are needed to support client authentication.

  `URLopener` objects will raise an `OSError` exception if the server returns an error code.

  `open`(fullurl, data=None)

    Open fullurl using the appropriate protocol. This method sets up cache and proxy information, then calls the appropriate open method with its input arguments. If the scheme is not recognized, `open_unknown()` is called. The data argument has the same meaning as the data argument of `urlopen()`.

    This method always quotes fullurl using `quote()`.

  `open_unknown`(fullurl, data=None)

    Overridable interface to open unknown URL types.

  `retrieve`(url, filename=None, reporthook=None, data=None)

    Retrieves the contents of url and places it in filename. The return value is a tuple consisting of a local filename and either an `email.message.Message` object containing the response headers (for remote URLs) or `None` (for local URLs). The caller must then open and read the contents of filename. If filename is not given and the URL refers to a local file, the input filename is returned. If the URL is non-local and filename is not given, the filename is the output of `tempfile.mktemp()` with a suffix that matches the suffix of the last path component of the input URL. If reporthook is given, it must be a function accepting three numeric parameters: A chunk number, the maximum size chunks are read in and the total size of the download (-1 if unknown). It will be called once at the start and after each chunk of data is read from the network. reporthook is ignored for local URLs.

    If the url uses the `http:` scheme identifier, the optional data argument may be given to specify a `POST` request (normally the request type is `GET`). The data argument must in standard application/x-www-form-urlencoded format; see the `urllib.parse.urlencode()` function.

  `version`

    Variable that specifies the user agent of the opener object. To get `urllib` to tell servers that it is a particular user agent, set this in a subclass as a class variable or in the constructor before calling the base constructor.

class `urllib.request.``FancyURLopener`(...)

  3.3 版后已移除.

  `FancyURLopener` subclasses `URLopener` providing default handling for the following HTTP response codes: 301, 302, 303, 307 and 401. For the 30x response codes listed above, the Location header is used to fetch the actual URL. For 401 response codes (authentication required), basic HTTP authentication is performed. For the 30x response codes, recursion is bounded by the value of the maxtries attribute, which defaults to 10.

  For all other response codes, the method `http_error_default()` is called which you can override in subclasses to handle the error appropriately.

  注解

  According to the letter of RFC 2616, 301 and 302 responses to POST requests must not be automatically redirected without confirmation by the user. In reality, browsers do allow automatic redirection of these responses, changing the POST to a GET, and `urllib` reproduces this behaviour.

  The parameters to the constructor are the same as those for `URLopener`.

  注解

  When performing basic authentication, a `FancyURLopener` instance calls its `prompt_user_passwd()` method. The default implementation asks the users for the required information on the controlling terminal. A subclass may override this method to support more appropriate behavior if needed.

  The `FancyURLopener` class offers one additional method that should be overloaded to provide the appropriate behavior:

  `prompt_user_passwd`(host, realm)

    Return information needed to authenticate the user at the given host in the specified security realm. The return value should be a tuple, `(user, password)`, which can be used for basic authentication.

    The implementation prompts for this information on the terminal; an application should override this method to use an appropriate interaction model in the local environment.

## `urllib.request` Restrictions

- Currently, only the following protocols are supported: HTTP (versions 0.9 and 1.0), FTP, local files, and data URLs.

  在 3.4 版更改: Added support for data URLs.

- The caching feature of `urlretrieve()` has been disabled until someone finds the time to hack proper processing of Expiration time headers.

- There should be a function to query whether a particular URL is in the cache.

- For backward compatibility, if a URL appears to point to a local file but the file can't be opened, the URL is re-interpreted using the FTP protocol. This can sometimes cause confusing error messages.

- The `urlopen()` and `urlretrieve()` functions can cause arbitrarily long delays while waiting for a network connection to be set up. This means that it is difficult to build an interactive Web client using these functions without using threads.

- The data returned by `urlopen()` or `urlretrieve()` is the raw data returned by the server. This may be binary data (such as an image), plain text or (for example) HTML. The HTTP protocol provides type information in the reply header, which can be inspected by looking at the Content-Type header. If the returned data is HTML, you can use the module `html.parser` to parse it.

- The code handling the FTP protocol cannot differentiate between a file and a directory. This can lead to unexpected behavior when attempting to read a URL that points to a file that is not accessible. If the URL ends in a `/`, it is assumed to refer to a directory and will be handled accordingly. But if an attempt to read a file leads to a 550 error (meaning the URL cannot be found or is not accessible, often for permission reasons), then the path is treated as a directory in order to handle the case when a directory is specified by a URL but the trailing `/` has been left off. This can cause misleading results when you try to fetch a file whose read permissions make it inaccessible; the FTP code will try to read it, fail with a 550 error, and then perform a directory listing for the unreadable file. If fine-grained control is needed, consider using the `ftplib` module, subclassing `FancyURLopener`, or changing _urlopener to meet your needs.

# `urllib.response` --- urllib 使用的 Response 类

The `urllib.response` module defines functions and classes which define a minimal file like interface, including `read()` and `readline()`. The typical response object is an addinfourl instance, which defines an `info()` method and that returns headers and a `geturl()` method that returns the url. Functions defined by this module are used internally by the `urllib.request` module.