如何使用urllib包獲取網絡資源 · Python3.7.3官方文檔簡體中文

### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](argparse.xhtml "Argparse 教程") | - [上一頁](unicode.xhtml "Unicode 指南") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 常用指引](index.xhtml) ? - $('.inline-search').show(0); | # 如何使用urllib包獲取網絡資源作者[Michael Foord](http://www.voidspace.org.uk/python/index.shtml) \[http://www.voidspace.org.uk/python/index.shtml\] 注解這份 HOWTO 文檔的早期版本有一份法語的譯文，可在 [urllib2 - Le Manuel manquant](http://www.voidspace.org.uk/python/articles/urllib2_francais.shtml) \[http://www.voidspace.org.uk/python/articles/urllib2\_francais.shtml\] 處查閱。 ## 概述 Related Articles 關于使用 Python 獲取網頁資源，你或許還可以找到下列有用的文章： - [基本的驗證](http://www.voidspace.org.uk/python/articles/authentication.shtml) \[http://www.voidspace.org.uk/python/articles/authentication.shtml\] > 關于 *基本的驗證* 的入門指南，帶有一些 Python 的示例。 **urllib.request** 是一個用于獲取 URL （統一資源定位地址）的 Python 模塊。它以 *urlopen* 函數的形式提供了一個非常簡單的接口。該接口能夠使用不同的協議獲取 URL。同時它也提供了一個略微復雜的接口來處理常見情形——如：基本驗證、cookies、代理等等。這些功能是通過叫做 handlers 和 opener 的對象來提供的。 urllib.request 支持多種 "URL 網址方案" （通過 URL中 `":"` 之前的字符串加以區分——如 URL 地址 `"ftp://python.org/"` 中的 ``"ftp"``），使用與之相關的網絡協議（如：FTP、 HTTP）來獲取 URL 資源。本指南重點關注最常用的情形—— HTTP。 For straightforward situations *urlopen* is very easy to use. But as soon as you encounter errors or non-trivial cases when opening HTTP URLs, you will need some understanding of the HyperText Transfer Protocol. The most comprehensive and authoritative reference to HTTP is [**RFC 2616**](https://tools.ietf.org/html/rfc2616.html) \[https://tools.ietf.org/html/rfc2616.html\]. This is a technical document and not intended to be easy to read. This HOWTO aims to illustrate using *urllib*, with enough detail about HTTP to help you through. It is not intended to replace the [`urllib.request`](../library/urllib.request.xhtml#module-urllib.request "urllib.request: Extensible library for opening URLs.") docs, but is supplementary to them. ## Fetching URLs 下面是使用 urllib.request 最簡單的方式： ``` import urllib.request with urllib.request.urlopen('http://python.org/') as response: html = response.read() ``` 如果你想通過 URL 獲取資源并保存某個臨時的地方，你可以通過 [`shutil.copyfileobj()`](../library/shutil.xhtml#shutil.copyfileobj "shutil.copyfileobj") 和 [`tempfile.NamedTemporaryFile()`](../library/tempfile.xhtml#tempfile.NamedTemporaryFile "tempfile.NamedTemporaryFile") 函數: ``` import shutil import tempfile import urllib.request with urllib.request.urlopen('http://python.org/') as response: with tempfile.NamedTemporaryFile(delete=False) as tmp_file: shutil.copyfileobj(response, tmp_file) with open(tmp_file.name) as html: pass ``` Many uses of urllib will be that simple (note that instead of an 'http:' URL we could have used a URL starting with 'ftp:', 'file:', etc.). However, it's the purpose of this tutorial to explain the more complicated cases, concentrating on HTTP. HTTP is based on requests and responses - the client makes requests and servers send responses. urllib.request mirrors this with a `Request` object which represents the HTTP request you are making. In its simplest form you create a Request object that specifies the URL you want to fetch. Calling `urlopen` with this Request object returns a response object for the URL requested. This response is a file-like object, which means you can for example call `.read()` on the response: ``` import urllib.request req = urllib.request.Request('http://www.voidspace.org.uk') with urllib.request.urlopen(req) as response: the_page = response.read() ``` Note that urllib.request makes use of the same Request interface to handle all URL schemes. For example, you can make an FTP request like so: ``` req = urllib.request.Request('ftp://example.com/') ``` In the case of HTTP, there are two extra things that Request objects allow you to do: First, you can pass data to be sent to the server. Second, you can pass extra information ("metadata") *about* the data or the about request itself, to the server - this information is sent as HTTP "headers". Let's look at each of these in turn. ### Data Sometimes you want to send data to a URL (often the URL will refer to a CGI (Common Gateway Interface) script or other web application). With HTTP, this is often done using what's known as a **POST** request. This is often what your browser does when you submit a HTML form that you filled in on the web. Not all POSTs have to come from forms: you can use a POST to transmit arbitrary data to your own application. In the common case of HTML forms, the data needs to be encoded in a standard way, and then passed to the Request object as the `data`argument. The encoding is done using a function from the [`urllib.parse`](../library/urllib.parse.xhtml#module-urllib.parse "urllib.parse: Parse URLs into or assemble them from components.")library. ``` import urllib.parse import urllib.request url = 'http://www.someserver.com/cgi-bin/register.cgi' values = {'name' : 'Michael Foord', 'location' : 'Northampton', 'language' : 'Python' } data = urllib.parse.urlencode(values) data = data.encode('ascii') # data should be bytes req = urllib.request.Request(url, data) with urllib.request.urlopen(req) as response: the_page = response.read() ``` Note that other encodings are sometimes required (e.g. for file upload from HTML forms - see [HTML Specification, Form Submission](https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13) \[https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13\] for more details). If you do not pass the `data` argument, urllib uses a **GET** request. One way in which GET and POST requests differ is that POST requests often have "side-effects": they change the state of the system in some way (for example by placing an order with the website for a hundredweight of tinned spam to be delivered to your door). Though the HTTP standard makes it clear that POSTs are intended to *always* cause side-effects, and GET requests *never* to cause side-effects, nothing prevents a GET request from having side-effects, nor a POST requests from having no side-effects. Data can also be passed in an HTTP GET request by encoding it in the URL itself. This is done as follows: ``` >>> import urllib.request >>> import urllib.parse >>> data = {} >>> data['name'] = 'Somebody Here' >>> data['location'] = 'Northampton' >>> data['language'] = 'Python' >>> url_values = urllib.parse.urlencode(data) >>> print(url_values) # The order may differ from below. name=Somebody+Here&language=Python&location=Northampton >>> url = 'http://www.example.com/example.cgi' >>> full_url = url + '?' + url_values >>> data = urllib.request.urlopen(full_url) ``` Notice that the full URL is created by adding a `?` to the URL, followed by the encoded values. ### Headers We'll discuss here one particular HTTP header, to illustrate how to add headers to your HTTP request. Some websites [1](#id8) dislike being browsed by programs, or send different versions to different browsers [2](#id9). By default urllib identifies itself as `Python-urllib/x.y` (where `x` and `y` are the major and minor version numbers of the Python release, e.g. `Python-urllib/2.5`), which may confuse the site, or just plain not work. The way a browser identifies itself is through the `User-Agent` header [3](#id10). When you create a Request object you can pass a dictionary of headers in. The following example makes the same request as above, but identifies itself as a version of Internet Explorer [4](#id11). ``` import urllib.parse import urllib.request url = 'http://www.someserver.com/cgi-bin/register.cgi' user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64)' values = {'name': 'Michael Foord', 'location': 'Northampton', 'language': 'Python' } headers = {'User-Agent': user_agent} data = urllib.parse.urlencode(values) data = data.encode('ascii') req = urllib.request.Request(url, data, headers) with urllib.request.urlopen(req) as response: the_page = response.read() ``` The response also has two useful methods. See the section on [info and geturl](#info-and-geturl)which comes after we have a look at what happens when things go wrong. ## 處理異常 *urlopen* raises `URLError` when it cannot handle a response (though as usual with Python APIs, built-in exceptions such as [`ValueError`](../library/exceptions.xhtml#ValueError "ValueError"), [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") etc. may also be raised). `HTTPError` is the subclass of `URLError` raised in the specific case of HTTP URLs. The exception classes are exported from the [`urllib.error`](../library/urllib.error.xhtml#module-urllib.error "urllib.error: Exception classes raised by urllib.request.") module. ### URLError 通常，引發 URLError 的原因是沒有網絡連接（或者沒有到指定服務器的路由），或者指定的服務器不存在。該情況下，將會引發該異常，并帶有一個 'reason' 屬性，該屬性是一個包含錯誤代碼和文本錯誤信息的元組。 e.g. ``` >>> req = urllib.request.Request('http://www.pretend_server.org') >>> try: urllib.request.urlopen(req) ... except urllib.error.URLError as e: ... print(e.reason) ... (4, 'getaddrinfo failed') ``` ### HTTPError 從服務器返回的每個 HTTP 響應都包含一個數字的 “狀態碼”。有時該狀態碼表明服務器無法完成該請求。默認的處理器（函數？）將會為你處理這其中的一些響應。（例如，如果響應包含了 "redirection"，將會要求客戶端去向另外的 URL 獲取文檔，urllib 將會為你處理該情形）。對于那些它無法處理的（狀態代碼），urlopen 將會引發一個 `HTTPError` 。典型的錯誤包括：‘404’（頁面無法找到）、‘403’（請求遭拒絕）和 ’401‘ （需要身份驗證）。 See section 10 of [**RFC 2616**](https://tools.ietf.org/html/rfc2616.html) \[https://tools.ietf.org/html/rfc2616.html\] for a reference on all the HTTP error codes. The `HTTPError` instance raised will have an integer 'code' attribute, which corresponds to the error sent by the server. #### Error Codes Because the default handlers handle redirects (codes in the 300 range), and codes in the 100--299 range indicate success, you will usually only see error codes in the 400--599 range. [`http.server.BaseHTTPRequestHandler.responses`](../library/http.server.xhtml#http.server.BaseHTTPRequestHandler.responses "http.server.BaseHTTPRequestHandler.responses") is a useful dictionary of response codes in that shows all the response codes used by [**RFC 2616**](https://tools.ietf.org/html/rfc2616.html) \[https://tools.ietf.org/html/rfc2616.html\]. The dictionary is reproduced here for convenience ``` # Table mapping response codes to messages; entries have the # form {code: (shortmessage, longmessage)}. responses = { 100: ('Continue', 'Request received, please continue'), 101: ('Switching Protocols', 'Switching to new protocol; obey Upgrade header'), 200: ('OK', 'Request fulfilled, document follows'), 201: ('Created', 'Document created, URL follows'), 202: ('Accepted', 'Request accepted, processing continues off-line'), 203: ('Non-Authoritative Information', 'Request fulfilled from cache'), 204: ('No Content', 'Request fulfilled, nothing follows'), 205: ('Reset Content', 'Clear input form for further input.'), 206: ('Partial Content', 'Partial content follows.'), 300: ('Multiple Choices', 'Object has several resources -- see URI list'), 301: ('Moved Permanently', 'Object moved permanently -- see URI list'), 302: ('Found', 'Object moved temporarily -- see URI list'), 303: ('See Other', 'Object moved -- see Method and URL list'), 304: ('Not Modified', 'Document has not changed since given time'), 305: ('Use Proxy', 'You must use proxy specified in Location to access this ' 'resource.'), 307: ('Temporary Redirect', 'Object moved temporarily -- see URI list'), 400: ('Bad Request', 'Bad request syntax or unsupported method'), 401: ('Unauthorized', 'No permission -- see authorization schemes'), 402: ('Payment Required', 'No payment -- see charging schemes'), 403: ('Forbidden', 'Request forbidden -- authorization will not help'), 404: ('Not Found', 'Nothing matches the given URI'), 405: ('Method Not Allowed', 'Specified method is invalid for this server.'), 406: ('Not Acceptable', 'URI not available in preferred format.'), 407: ('Proxy Authentication Required', 'You must authenticate with ' 'this proxy before proceeding.'), 408: ('Request Timeout', 'Request timed out; try again later.'), 409: ('Conflict', 'Request conflict.'), 410: ('Gone', 'URI no longer exists and has been permanently removed.'), 411: ('Length Required', 'Client must specify Content-Length.'), 412: ('Precondition Failed', 'Precondition in headers is false.'), 413: ('Request Entity Too Large', 'Entity is too large.'), 414: ('Request-URI Too Long', 'URI is too long.'), 415: ('Unsupported Media Type', 'Entity body in unsupported format.'), 416: ('Requested Range Not Satisfiable', 'Cannot satisfy request range.'), 417: ('Expectation Failed', 'Expect condition could not be satisfied.'), 500: ('Internal Server Error', 'Server got itself in trouble'), 501: ('Not Implemented', 'Server does not support this operation'), 502: ('Bad Gateway', 'Invalid responses from another server/proxy.'), 503: ('Service Unavailable', 'The server cannot process the request due to a high load'), 504: ('Gateway Timeout', 'The gateway server did not receive a timely response'), 505: ('HTTP Version Not Supported', 'Cannot fulfill request.'), } ``` When an error is raised the server responds by returning an HTTP error code *and* an error page. You can use the `HTTPError` instance as a response on the page returned. This means that as well as the code attribute, it also has read, geturl, and info, methods as returned by the `urllib.response` module: ``` >>> req = urllib.request.Request('http://www.python.org/fish.html') >>> try: ... urllib.request.urlopen(req) ... except urllib.error.HTTPError as e: ... print(e.code) ... print(e.read()) ... 404 b'\n\n\n<html ... <title>Page Not Found</title>\n ... ``` ### Wrapping it Up So if you want to be prepared for `HTTPError` *or*`URLError` there are two basic approaches. I prefer the second approach. #### Number 1 ``` from urllib.request import Request, urlopen from urllib.error import URLError, HTTPError req = Request(someurl) try: response = urlopen(req) except HTTPError as e: print('The server couldn\'t fulfill the request.') print('Error code: ', e.code) except URLError as e: print('We failed to reach a server.') print('Reason: ', e.reason) else: # everything is fine ``` 注解 The `except HTTPError` *must* come first, otherwise `except URLError`will *also* catch an `HTTPError`. #### Number 2 ``` from urllib.request import Request, urlopen from urllib.error import URLError req = Request(someurl) try: response = urlopen(req) except URLError as e: if hasattr(e, 'reason'): print('We failed to reach a server.') print('Reason: ', e.reason) elif hasattr(e, 'code'): print('The server couldn\'t fulfill the request.') print('Error code: ', e.code) else: # everything is fine ``` ## info and geturl 由 urlopen （或者 `HTTPError` 實例）所返回的響應包含兩個有用的方法： `info()` 和 `geturl()`，該響應由模塊 [`urllib.response`](../library/urllib.request.xhtml#module-urllib.response "urllib.response: Response classes used by urllib.") 定義。 **geturl** - 返回所獲取頁面的真實 URL。該方法很有用，因為 `urlopen` （或者所使用的 opener 對象）可能回包括一次重定向。所獲取頁面的 URL 未必就是所請求的 URL 。 **info** - 該方法返回一個類似字典的對象，描述了所獲取的頁面，特別是由服務器送出的頭部信息（headers）。目前它是一個 `http.client.HTTPMessage` 實例。 Typical headers include 'Content-length', 'Content-type', and so on. See the [Quick Reference to HTTP Headers](http://jkorpela.fi/http.html) \[http://jkorpela.fi/http.html\]for a useful listing of HTTP headers with brief explanations of their meaning and use. ## Openers and Handlers When you fetch a URL you use an opener (an instance of the perhaps confusingly-named [`urllib.request.OpenerDirector`](../library/urllib.request.xhtml#urllib.request.OpenerDirector "urllib.request.OpenerDirector")). Normally we have been using the default opener - via `urlopen` - but you can create custom openers. Openers use handlers. All the "heavy lifting" is done by the handlers. Each handler knows how to open URLs for a particular URL scheme (http, ftp, etc.), or how to handle an aspect of URL opening, for example HTTP redirections or HTTP cookies. You will want to create openers if you want to fetch URLs with specific handlers installed, for example to get an opener that handles cookies, or to get an opener that does not handle redirections. To create an opener, instantiate an `OpenerDirector`, and then call `.add_handler(some_handler_instance)` repeatedly. Alternatively, you can use `build_opener`, which is a convenience function for creating opener objects with a single function call. `build_opener` adds several handlers by default, but provides a quick way to add more and/or override the default handlers. Other sorts of handlers you might want to can handle proxies, authentication, and other common but slightly specialised situations. `install_opener` can be used to make an `opener` object the (global) default opener. This means that calls to `urlopen` will use the opener you have installed. Opener objects have an `open` method, which can be called directly to fetch urls in the same way as the `urlopen` function: there's no need to call `install_opener`, except as a convenience. ## Basic Authentication To illustrate creating and installing a handler we will use the `HTTPBasicAuthHandler`. For a more detailed discussion of this subject -- including an explanation of how Basic Authentication works - see the [Basic Authentication Tutorial](http://www.voidspace.org.uk/python/articles/authentication.shtml) \[http://www.voidspace.org.uk/python/articles/authentication.shtml\]. When authentication is required, the server sends a header (as well as the 401 error code) requesting authentication. This specifies the authentication scheme and a 'realm'. The header looks like: ``` WWW-Authenticate: SCHEME realm="REALM" ``` . e.g. ``` WWW-Authenticate: Basic realm="cPanel Users" ``` The client should then retry the request with the appropriate name and password for the realm included as a header in the request. This is 'basic authentication'. In order to simplify this process we can create an instance of `HTTPBasicAuthHandler` and an opener to use this handler. The `HTTPBasicAuthHandler` uses an object called a password manager to handle the mapping of URLs and realms to passwords and usernames. If you know what the realm is (from the authentication header sent by the server), then you can use a `HTTPPasswordMgr`. Frequently one doesn't care what the realm is. In that case, it is convenient to use `HTTPPasswordMgrWithDefaultRealm`. This allows you to specify a default username and password for a URL. This will be supplied in the absence of you providing an alternative combination for a specific realm. We indicate this by providing `None` as the realm argument to the `add_password` method. The top-level URL is the first URL that requires authentication. URLs "deeper" than the URL you pass to .add\_password() will also match. ``` # create a password manager password_mgr = urllib.request.HTTPPasswordMgrWithDefaultRealm() # Add the username and password. # If we knew the realm, we could use it instead of None. top_level_url = "http://example.com/foo/" password_mgr.add_password(None, top_level_url, username, password) handler = urllib.request.HTTPBasicAuthHandler(password_mgr) # create "opener" (OpenerDirector instance) opener = urllib.request.build_opener(handler) # use the opener to fetch a URL opener.open(a_url) # Install the opener. # Now all calls to urllib.request.urlopen use our opener. urllib.request.install_opener(opener) ``` 注解 In the above example we only supplied our `HTTPBasicAuthHandler` to `build_opener`. By default openers have the handlers for normal situations -- `ProxyHandler` (if a proxy setting such as an `http_proxy`environment variable is set), `UnknownHandler`, `HTTPHandler`, `HTTPDefaultErrorHandler`, `HTTPRedirectHandler`, `FTPHandler`, `FileHandler`, `DataHandler`, `HTTPErrorProcessor`. `top_level_url` is in fact *either* a full URL (including the 'http:' scheme component and the hostname and optionally the port number) e.g. `"http://example.com/"` *or* an "authority" (i.e. the hostname, optionally including the port number) e.g. `"example.com"` or `"example.com:8080"`(the latter example includes a port number). The authority, if present, must NOT contain the "userinfo" component - for example `"joe:password@example.com"` is not correct. ## Proxies **urllib** will auto-detect your proxy settings and use those. This is through the `ProxyHandler`, which is part of the normal handler chain when a proxy setting is detected. Normally that's a good thing, but there are occasions when it may not be helpful [5](#id12). One way to do this is to setup our own `ProxyHandler`, with no proxies defined. This is done using similar steps to setting up a [Basic Authentication](#basic-authentication) handler: ``` >>> proxy_support = urllib.request.ProxyHandler({}) >>> opener = urllib.request.build_opener(proxy_support) >>> urllib.request.install_opener(opener) ``` 注解 Currently `urllib.request` *does not* support fetching of `https` locations through a proxy. However, this can be enabled by extending urllib.request as shown in the recipe [6](#id13). 注解 `HTTP_PROXY` will be ignored if a variable `REQUEST_METHOD` is set; see the documentation on [`getproxies()`](../library/urllib.request.xhtml#urllib.request.getproxies "urllib.request.getproxies"). ## Sockets and Layers The Python support for fetching resources from the web is layered. urllib uses the [`http.client`](../library/http.client.xhtml#module-http.client "http.client: HTTP and HTTPS protocol client (requires sockets).") library, which in turn uses the socket library. As of Python 2.3 you can specify how long a socket should wait for a response before timing out. This can be useful in applications which have to fetch web pages. By default the socket module has *no timeout* and can hang. Currently, the socket timeout is not exposed at the http.client or urllib.request levels. However, you can set the default timeout globally for all sockets using ``` import socket import urllib.request # timeout in seconds timeout = 10 socket.setdefaulttimeout(timeout) # this call to urllib.request.urlopen now uses the default timeout # we have set in the socket module req = urllib.request.Request('http://www.voidspace.org.uk') response = urllib.request.urlopen(req) ``` - - - - - - ## 腳注 This document was reviewed and revised by John Lee. [1](#id1)Google for example. [2](#id2)Browser sniffing is a very bad practice for website design - building sites using web standards is much more sensible. Unfortunately a lot of sites still send different versions to different browsers. [3](#id3)The user agent for MSIE 6 is *'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)'* [4](#id4)For details of more HTTP request headers, see [Quick Reference to HTTP Headers](http://jkorpela.fi/http.html) \[http://jkorpela.fi/http.html\]. [5](#id6)In my case I have to use a proxy to access the internet at work. If you attempt to fetch *localhost* URLs through this proxy it blocks them. IE is set to use the proxy, which urllib picks up on. In order to test scripts with a localhost server, I have to prevent urllib from using the proxy. [6](#id7)urllib opener for SSL proxy (CONNECT method): [ASPN Cookbook Recipe](https://code.activestate.com/recipes/456195/) \[https://code.activestate.com/recipes/456195/\]. ### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](argparse.xhtml "Argparse 教程") | - [上一頁](unicode.xhtml "Unicode 指南") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 常用指引](index.xhtml) ? - $('.inline-search').show(0); | ? [版權所有](../copyright.xhtml) 2001-2019, Python Software Foundation. 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