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 <div class="section" id="howto-fetch-internet-resources-using-the-urllib-package">
<h1>HOWTO Fetch Internet Resources Using The urllib Package<a class="headerlink" href="#howto-fetch-internet-resources-using-the-urllib-package" title="Permalink to this headline">¶</a></h1>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Author:</th><td class="field-body"><a class="reference external" href="http://www.voidspace.org.uk/python/index.shtml">Michael Foord</a></td>
</tr>
</tbody>
</table>
<div class="admonition note">
Note
There is a French translation of an earlier revision of this
HOWTO, available at <a class="reference external" href="http://www.voidspace.org.uk/python/articles/urllib2_francais.shtml">urllib2 - Le Manuel manquant</a>.
</div>
<div class="section" id="introduction">
<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
<div class="sidebar">
Related Articles
You may also find useful the following article on fetching web resources
with Python:
<ul class="last">
<li><a class="reference external" href="http://www.voidspace.org.uk/python/articles/authentication.shtml">Basic Authentication</a>
<blockquote>
<div>A tutorial on Basic Authentication, with examples in Python.
</div></blockquote>
</li>
</ul>
</div>
urllib.request is a Python module for fetching URLs
(Uniform Resource Locators). It offers a very simple interface, in the form of
the urlopen function. This is capable of fetching URLs using a variety of
different protocols. It also offers a slightly more complex interface for
handling common situations - like basic authentication, cookies, proxies and so
on. These are provided by objects called handlers and openers.
urllib.request supports fetching URLs for many “URL schemes” (identified by the string
before the <code class="docutils literal notranslate">&quot;:&quot;</code> in URL - for example <code class="docutils literal notranslate">&quot;ftp&quot;</code> is the URL scheme of
<code class="docutils literal notranslate">&quot;ftp://python.org/&quot;</code>) using their associated network protocols (e.g. FTP, HTTP).
This tutorial focuses on the most common case, 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 <a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html">RFC 2616</a>. 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 <a class="reference internal" href="../library/urllib.request.html#module-urllib.request" title="urllib.request: Extensible library for opening URLs."><code class="xref py py-mod docutils literal notranslate">urllib.request</code></a> docs, but is supplementary to them.
</div>
<div class="section" id="fetching-urls">
<h2>Fetching URLs<a class="headerlink" href="#fetching-urls" title="Permalink to this headline">¶</a></h2>
The simplest way to use urllib.request is as follows:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import urllib.request
with urllib.request.urlopen(&#39;http://python.org/&#39;) as response:
 html = response.read()
</pre></div>
</div>
If you wish to retrieve a resource via URL and store it in a temporary
location, you can do so via the <a class="reference internal" href="../library/shutil.html#shutil.copyfileobj" title="shutil.copyfileobj"><code class="xref py py-func docutils literal notranslate">shutil.copyfileobj()</code></a> and
<a class="reference internal" href="../library/tempfile.html#tempfile.NamedTemporaryFile" title="tempfile.NamedTemporaryFile"><code class="xref py py-func docutils literal notranslate">tempfile.NamedTemporaryFile()</code></a> functions:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import shutil
import tempfile
import urllib.request

with urllib.request.urlopen(&#39;http://python.org/&#39;) as response:
 with tempfile.NamedTemporaryFile(delete=False) as tmp_file:
 shutil.copyfileobj(response, tmp_file)

with open(tmp_file.name) as html:
 pass
</pre></div>
</div>
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 <code class="docutils literal notranslate">Request</code> 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 <code class="docutils literal notranslate">urlopen</code> 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 <code class="docutils literal notranslate">.read()</code> on the
response:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import urllib.request

req = urllib.request.Request(&#39;http://www.voidspace.org.uk&#39;)
with urllib.request.urlopen(req) as response:
 the_page = response.read()
</pre></div>
</div>
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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>req = urllib.request.Request(&#39;ftp://example.com/&#39;)
</pre></div>
</div>
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.
<div class="section" id="data">
<h3>Data<a class="headerlink" href="#data" title="Permalink to this headline">¶</a></h3>
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 <code class="docutils literal notranslate">data</code>
argument. The encoding is done using a function from the <a class="reference internal" href="../library/urllib.parse.html#module-urllib.parse" title="urllib.parse: Parse URLs into or assemble them from components."><code class="xref py py-mod docutils literal notranslate">urllib.parse</code></a>
library.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import urllib.parse
import urllib.request

url = &#39;http://www.someserver.com/cgi-bin/register.cgi&#39;
values = {&#39;name&#39; : &#39;Michael Foord&#39;,
 &#39;location&#39; : &#39;Northampton&#39;,
 &#39;language&#39; : &#39;Python&#39; }

data = urllib.parse.urlencode(values)
data = data.encode(&#39;ascii&#39;) # data should be bytes
req = urllib.request.Request(url, data)
with urllib.request.urlopen(req) as response:
 the_page = response.read()
</pre></div>
</div>
Note that other encodings are sometimes required (e.g. for file upload from HTML
forms - see <a class="reference external" href="https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13">HTML Specification, Form Submission</a> for more
details).
If you do not pass the <code class="docutils literal notranslate">data</code> 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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import urllib.request
&gt;&gt;&gt; import urllib.parse
&gt;&gt;&gt; data = {}
&gt;&gt;&gt; data[&#39;name&#39;] = &#39;Somebody Here&#39;
&gt;&gt;&gt; data[&#39;location&#39;] = &#39;Northampton&#39;
&gt;&gt;&gt; data[&#39;language&#39;] = &#39;Python&#39;
&gt;&gt;&gt; url_values = urllib.parse.urlencode(data)
&gt;&gt;&gt; print(url_values) # The order may differ from below. 
name=Somebody+Here&amp;language=Python&amp;location=Northampton
&gt;&gt;&gt; url = &#39;http://www.example.com/example.cgi&#39;
&gt;&gt;&gt; full_url = url + &#39;?&#39; + url_values
&gt;&gt;&gt; data = urllib.request.urlopen(full_url)
</pre></div>
</div>
Notice that the full URL is created by adding a <code class="docutils literal notranslate">?</code> to the URL, followed by
the encoded values.
</div>
<div class="section" id="headers">
<h3>Headers<a class="headerlink" href="#headers" title="Permalink to this headline">¶</a></h3>
We’ll discuss here one particular HTTP header, to illustrate how to add headers
to your HTTP request.
Some websites <a class="footnote-reference" href="#id8" id="id1">[1]</a> dislike being browsed by programs, or send different versions
to different browsers <a class="footnote-reference" href="#id9" id="id2">[2]</a>. By default urllib identifies itself as
<code class="docutils literal notranslate">Python-urllib/x.y</code> (where <code class="docutils literal notranslate">x</code> and <code class="docutils literal notranslate">y</code> are the major and minor version
numbers of the Python release,
e.g. <code class="docutils literal notranslate">Python-urllib/2.5</code>), which may confuse the site, or just plain
not work. The way a browser identifies itself is through the
<code class="docutils literal notranslate">User-Agent</code> header <a class="footnote-reference" href="#id10" id="id3">[3]</a>. 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 <a class="footnote-reference" href="#id11" id="id4">[4]</a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import urllib.parse
import urllib.request

url = &#39;http://www.someserver.com/cgi-bin/register.cgi&#39;
user_agent = &#39;Mozilla/5.0 (Windows NT 6.1; Win64; x64)&#39;
values = {&#39;name&#39;: &#39;Michael Foord&#39;,
 &#39;location&#39;: &#39;Northampton&#39;,
 &#39;language&#39;: &#39;Python&#39; }
headers = {&#39;User-Agent&#39;: user_agent}

data = urllib.parse.urlencode(values)
data = data.encode(&#39;ascii&#39;)
req = urllib.request.Request(url, data, headers)
with urllib.request.urlopen(req) as response:
 the_page = response.read()
</pre></div>
</div>
The response also has two useful methods. See the section on <a class="reference internal" href="#info-and-geturl">info and geturl</a>
which comes after we have a look at what happens when things go wrong.
</div>
</div>
<div class="section" id="handling-exceptions">
<h2>Handling Exceptions<a class="headerlink" href="#handling-exceptions" title="Permalink to this headline">¶</a></h2>
urlopen raises <code class="xref py py-exc docutils literal notranslate">URLError</code> when it cannot handle a response (though as
usual with Python APIs, built-in exceptions such as <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>,
<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> etc. may also be raised).
<code class="xref py py-exc docutils literal notranslate">HTTPError</code> is the subclass of <code class="xref py py-exc docutils literal notranslate">URLError</code> raised in the specific case of
HTTP URLs.
The exception classes are exported from the <a class="reference internal" href="../library/urllib.error.html#module-urllib.error" title="urllib.error: Exception classes raised by urllib.request."><code class="xref py py-mod docutils literal notranslate">urllib.error</code></a> module.
<div class="section" id="urlerror">
<h3>URLError<a class="headerlink" href="#urlerror" title="Permalink to this headline">¶</a></h3>
Often, URLError is raised because there is no network connection (no route to
the specified server), or the specified server doesn’t exist. In this case, the
exception raised will have a ‘reason’ attribute, which is a tuple containing an
error code and a text error message.
e.g.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; req = urllib.request.Request(&#39;http://www.pretend_server.org&#39;)
&gt;&gt;&gt; try: urllib.request.urlopen(req)
... except urllib.error.URLError as e:
... print(e.reason) 
...
(4, &#39;getaddrinfo failed&#39;)
</pre></div>
</div>
</div>
<div class="section" id="httperror">
<h3>HTTPError<a class="headerlink" href="#httperror" title="Permalink to this headline">¶</a></h3>
Every HTTP response from the server contains a numeric “status code”. Sometimes
the status code indicates that the server is unable to fulfil the request. The
default handlers will handle some of these responses for you (for example, if
the response is a “redirection” that requests the client fetch the document from
a different URL, urllib will handle that for you). For those it can’t handle,
urlopen will raise an <code class="xref py py-exc docutils literal notranslate">HTTPError</code>. Typical errors include ‘404’ (page not
found), ‘403’ (request forbidden), and ‘401’ (authentication required).
See section 10 of <a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html">RFC 2616</a> for a reference on all the HTTP error codes.
The <code class="xref py py-exc docutils literal notranslate">HTTPError</code> instance raised will have an integer ‘code’ attribute, which
corresponds to the error sent by the server.
<div class="section" id="error-codes">
<h4>Error Codes<a class="headerlink" href="#error-codes" title="Permalink to this headline">¶</a></h4>
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.
<a class="reference internal" href="../library/http.server.html#http.server.BaseHTTPRequestHandler.responses" title="http.server.BaseHTTPRequestHandler.responses"><code class="xref py py-attr docutils literal notranslate">http.server.BaseHTTPRequestHandler.responses</code></a> is a useful dictionary of
response codes in that shows all the response codes used by <a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html">RFC 2616</a>. The
dictionary is reproduced here for convenience
<div class="highlight-python3 notranslate"><div class="highlight"><pre># Table mapping response codes to messages; entries have the
# form {code: (shortmessage, longmessage)}.
responses = {
 100: (&#39;Continue&#39;, &#39;Request received, please continue&#39;),
 101: (&#39;Switching Protocols&#39;,
 &#39;Switching to new protocol; obey Upgrade header&#39;),

200: (&#39;OK&#39;, &#39;Request fulfilled, document follows&#39;),
 201: (&#39;Created&#39;, &#39;Document created, URL follows&#39;),
 202: (&#39;Accepted&#39;,
 &#39;Request accepted, processing continues off-line&#39;),
 203: (&#39;Non-Authoritative Information&#39;, &#39;Request fulfilled from cache&#39;),
 204: (&#39;No Content&#39;, &#39;Request fulfilled, nothing follows&#39;),
 205: (&#39;Reset Content&#39;, &#39;Clear input form for further input.&#39;),
 206: (&#39;Partial Content&#39;, &#39;Partial content follows.&#39;),

300: (&#39;Multiple Choices&#39;,
 &#39;Object has several resources -- see URI list&#39;),
 301: (&#39;Moved Permanently&#39;, &#39;Object moved permanently -- see URI list&#39;),
 302: (&#39;Found&#39;, &#39;Object moved temporarily -- see URI list&#39;),
 303: (&#39;See Other&#39;, &#39;Object moved -- see Method and URL list&#39;),
 304: (&#39;Not Modified&#39;,
 &#39;Document has not changed since given time&#39;),
 305: (&#39;Use Proxy&#39;,
 &#39;You must use proxy specified in Location to access this &#39;
 &#39;resource.&#39;),
 307: (&#39;Temporary Redirect&#39;,
 &#39;Object moved temporarily -- see URI list&#39;),

400: (&#39;Bad Request&#39;,
 &#39;Bad request syntax or unsupported method&#39;),
 401: (&#39;Unauthorized&#39;,
 &#39;No permission -- see authorization schemes&#39;),
 402: (&#39;Payment Required&#39;,
 &#39;No payment -- see charging schemes&#39;),
 403: (&#39;Forbidden&#39;,
 &#39;Request forbidden -- authorization will not help&#39;),
 404: (&#39;Not Found&#39;, &#39;Nothing matches the given URI&#39;),
 405: (&#39;Method Not Allowed&#39;,
 &#39;Specified method is invalid for this server.&#39;),
 406: (&#39;Not Acceptable&#39;, &#39;URI not available in preferred format.&#39;),
 407: (&#39;Proxy Authentication Required&#39;, &#39;You must authenticate with &#39;
 &#39;this proxy before proceeding.&#39;),
 408: (&#39;Request Timeout&#39;, &#39;Request timed out; try again later.&#39;),
 409: (&#39;Conflict&#39;, &#39;Request conflict.&#39;),
 410: (&#39;Gone&#39;,
 &#39;URI no longer exists and has been permanently removed.&#39;),
 411: (&#39;Length Required&#39;, &#39;Client must specify Content-Length.&#39;),
 412: (&#39;Precondition Failed&#39;, &#39;Precondition in headers is false.&#39;),
 413: (&#39;Request Entity Too Large&#39;, &#39;Entity is too large.&#39;),
 414: (&#39;Request-URI Too Long&#39;, &#39;URI is too long.&#39;),
 415: (&#39;Unsupported Media Type&#39;, &#39;Entity body in unsupported format.&#39;),
 416: (&#39;Requested Range Not Satisfiable&#39;,
 &#39;Cannot satisfy request range.&#39;),
 417: (&#39;Expectation Failed&#39;,
 &#39;Expect condition could not be satisfied.&#39;),

500: (&#39;Internal Server Error&#39;, &#39;Server got itself in trouble&#39;),
 501: (&#39;Not Implemented&#39;,
 &#39;Server does not support this operation&#39;),
 502: (&#39;Bad Gateway&#39;, &#39;Invalid responses from another server/proxy.&#39;),
 503: (&#39;Service Unavailable&#39;,
 &#39;The server cannot process the request due to a high load&#39;),
 504: (&#39;Gateway Timeout&#39;,
 &#39;The gateway server did not receive a timely response&#39;),
 505: (&#39;HTTP Version Not Supported&#39;, &#39;Cannot fulfill request.&#39;),
 }
</pre></div>
</div>
When an error is raised the server responds by returning an HTTP error code
and an error page. You can use the <code class="xref py py-exc docutils literal notranslate">HTTPError</code> 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 <code class="docutils literal notranslate">urllib.response</code> module:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; req = urllib.request.Request(&#39;http://www.python.org/fish.html&#39;)
&gt;&gt;&gt; try:
... urllib.request.urlopen(req)
... except urllib.error.HTTPError as e:
... print(e.code)
... print(e.read()) 
...
404
b&#39;&lt;!DOCTYPE html PUBLIC &quot;-//W3C//DTD XHTML 1.0 Transitional//EN&quot;
 &quot;http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd&quot;&gt;\n\n\n&lt;html
 ...
 &lt;title&gt;Page Not Found&lt;/title&gt;\n
 ...
</pre></div>
</div>
</div>
</div>
<div class="section" id="wrapping-it-up">
<h3>Wrapping it Up<a class="headerlink" href="#wrapping-it-up" title="Permalink to this headline">¶</a></h3>
So if you want to be prepared for <code class="xref py py-exc docutils literal notranslate">HTTPError</code> or <code class="xref py py-exc docutils literal notranslate">URLError</code> there are two
basic approaches. I prefer the second approach.
<div class="section" id="number-1">
<h4>Number 1<a class="headerlink" href="#number-1" title="Permalink to this headline">¶</a></h4>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>from urllib.request import Request, urlopen
from urllib.error import URLError, HTTPError
req = Request(someurl)
try:
 response = urlopen(req)
except HTTPError as e:
 print(&#39;The server couldn\&#39;t fulfill the request.&#39;)
 print(&#39;Error code: &#39;, e.code)
except URLError as e:
 print(&#39;We failed to reach a server.&#39;)
 print(&#39;Reason: &#39;, e.reason)
else:
 # everything is fine
</pre></div>
</div>
<div class="admonition note">
Note
The <code class="docutils literal notranslate">except HTTPError</code> must come first, otherwise <code class="docutils literal notranslate">except URLError</code>
will also catch an <code class="xref py py-exc docutils literal notranslate">HTTPError</code>.
</div>
</div>
<div class="section" id="number-2">
<h4>Number 2<a class="headerlink" href="#number-2" title="Permalink to this headline">¶</a></h4>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>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, &#39;reason&#39;):
 print(&#39;We failed to reach a server.&#39;)
 print(&#39;Reason: &#39;, e.reason)
 elif hasattr(e, &#39;code&#39;):
 print(&#39;The server couldn\&#39;t fulfill the request.&#39;)
 print(&#39;Error code: &#39;, e.code)
else:
 # everything is fine
</pre></div>
</div>
</div>
</div>
</div>
<div class="section" id="info-and-geturl">
<h2>info and geturl<a class="headerlink" href="#info-and-geturl" title="Permalink to this headline">¶</a></h2>
The response returned by urlopen (or the <code class="xref py py-exc docutils literal notranslate">HTTPError</code> instance) has two
useful methods <code class="xref py py-meth docutils literal notranslate">info()</code> and <code class="xref py py-meth docutils literal notranslate">geturl()</code> and is defined in the module
<a class="reference internal" href="../library/urllib.request.html#module-urllib.response" title="urllib.response: Response classes used by urllib."><code class="xref py py-mod docutils literal notranslate">urllib.response</code></a>..
geturl - this returns the real URL of the page fetched. This is useful
because <code class="docutils literal notranslate">urlopen</code> (or the opener object used) may have followed a
redirect. The URL of the page fetched may not be the same as the URL requested.
info - this returns a dictionary-like object that describes the page
fetched, particularly the headers sent by the server. It is currently an
<code class="xref py py-class docutils literal notranslate">http.client.HTTPMessage</code> instance.
Typical headers include ‘Content-length’, ‘Content-type’, and so on. See the
<a class="reference external" href="https://www.cs.tut.fi/~jkorpela/http.html">Quick Reference to HTTP Headers</a>
for a useful listing of HTTP headers with brief explanations of their meaning
and use.
</div>
<div class="section" id="openers-and-handlers">
<h2>Openers and Handlers<a class="headerlink" href="#openers-and-handlers" title="Permalink to this headline">¶</a></h2>
When you fetch a URL you use an opener (an instance of the perhaps
confusingly-named <a class="reference internal" href="../library/urllib.request.html#urllib.request.OpenerDirector" title="urllib.request.OpenerDirector"><code class="xref py py-class docutils literal notranslate">urllib.request.OpenerDirector</code></a>). Normally we have been using
the default opener - via <code class="docutils literal notranslate">urlopen</code> - 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 <code class="docutils literal notranslate">OpenerDirector</code>, and then call
<code class="docutils literal notranslate">.add_handler(some_handler_instance)</code> repeatedly.
Alternatively, you can use <code class="docutils literal notranslate">build_opener</code>, which is a convenience function for
creating opener objects with a single function call. <code class="docutils literal notranslate">build_opener</code> 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.
<code class="docutils literal notranslate">install_opener</code> can be used to make an <code class="docutils literal notranslate">opener</code> object the (global) default
opener. This means that calls to <code class="docutils literal notranslate">urlopen</code> will use the opener you have
installed.
Opener objects have an <code class="docutils literal notranslate">open</code> method, which can be called directly to fetch
urls in the same way as the <code class="docutils literal notranslate">urlopen</code> function: there’s no need to call
<code class="docutils literal notranslate">install_opener</code>, except as a convenience.
</div>
<div class="section" id="id5">
<h2>Basic Authentication<a class="headerlink" href="#id5" title="Permalink to this headline">¶</a></h2>
To illustrate creating and installing a handler we will use the
<code class="docutils literal notranslate">HTTPBasicAuthHandler</code>. For a more detailed discussion of this subject –
including an explanation of how Basic Authentication works - see the <a class="reference external" href="http://www.voidspace.org.uk/python/articles/authentication.shtml">Basic
Authentication Tutorial</a>.
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: <code class="docutils literal notranslate">WWW-Authenticate: SCHEME
realm=&quot;REALM&quot;</code>.
e.g.
<div class="highlight-none notranslate"><div class="highlight"><pre>WWW-Authenticate: Basic realm=&quot;cPanel Users&quot;
</pre></div>
</div>
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
<code class="docutils literal notranslate">HTTPBasicAuthHandler</code> and an opener to use this handler.
The <code class="docutils literal notranslate">HTTPBasicAuthHandler</code> 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
<code class="docutils literal notranslate">HTTPPasswordMgr</code>. Frequently one doesn’t care what the realm is. In that
case, it is convenient to use <code class="docutils literal notranslate">HTTPPasswordMgrWithDefaultRealm</code>. 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 <code class="docutils literal notranslate">None</code> as the realm argument to the
<code class="docutils literal notranslate">add_password</code> 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.
<div class="highlight-python3 notranslate"><div class="highlight"><pre># 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 = &quot;http://example.com/foo/&quot;
password_mgr.add_password(None, top_level_url, username, password)

handler = urllib.request.HTTPBasicAuthHandler(password_mgr)

# create &quot;opener&quot; (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)
</pre></div>
</div>
<div class="admonition note">
Note
In the above example we only supplied our <code class="docutils literal notranslate">HTTPBasicAuthHandler</code> to
<code class="docutils literal notranslate">build_opener</code>. By default openers have the handlers for normal situations
– <code class="docutils literal notranslate">ProxyHandler</code> (if a proxy setting such as an <code class="xref std std-envvar docutils literal notranslate">http_proxy</code>
environment variable is set), <code class="docutils literal notranslate">UnknownHandler</code>, <code class="docutils literal notranslate">HTTPHandler</code>,
<code class="docutils literal notranslate">HTTPDefaultErrorHandler</code>, <code class="docutils literal notranslate">HTTPRedirectHandler</code>, <code class="docutils literal notranslate">FTPHandler</code>,
<code class="docutils literal notranslate">FileHandler</code>, <code class="docutils literal notranslate">DataHandler</code>, <code class="docutils literal notranslate">HTTPErrorProcessor</code>.
</div>
<code class="docutils literal notranslate">top_level_url</code> is in fact either a full URL (including the ‘http:’ scheme
component and the hostname and optionally the port number)
e.g. <code class="docutils literal notranslate">&quot;http://example.com/&quot;</code> or an “authority” (i.e. the hostname,
optionally including the port number) e.g. <code class="docutils literal notranslate">&quot;example.com&quot;</code> or <code class="docutils literal notranslate">&quot;example.com:8080&quot;</code>
(the latter example includes a port number). The authority, if present, must
NOT contain the “userinfo” component - for example <code class="docutils literal notranslate">&quot;joe:password&#64;example.com&quot;</code> is
not correct.
</div>
<div class="section" id="proxies">
<h2>Proxies<a class="headerlink" href="#proxies" title="Permalink to this headline">¶</a></h2>
urllib will auto-detect your proxy settings and use those. This is through
the <code class="docutils literal notranslate">ProxyHandler</code>, 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 <a class="footnote-reference" href="#id12" id="id6">[5]</a>. One way to do this is to setup our own
<code class="docutils literal notranslate">ProxyHandler</code>, with no proxies defined. This is done using similar steps to
setting up a <a class="reference external" href="http://www.voidspace.org.uk/python/articles/authentication.shtml">Basic Authentication</a> handler:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; proxy_support = urllib.request.ProxyHandler({})
&gt;&gt;&gt; opener = urllib.request.build_opener(proxy_support)
&gt;&gt;&gt; urllib.request.install_opener(opener)
</pre></div>
</div>
<div class="admonition note">
Note
Currently <code class="docutils literal notranslate">urllib.request</code> does not support fetching of <code class="docutils literal notranslate">https</code> locations
through a proxy. However, this can be enabled by extending urllib.request as
shown in the recipe <a class="footnote-reference" href="#id13" id="id7">[6]</a>.
</div>
<div class="admonition note">
Note
<code class="docutils literal notranslate">HTTP_PROXY</code> will be ignored if a variable <code class="docutils literal notranslate">REQUEST_METHOD</code> is set; see
the documentation on <a class="reference internal" href="../library/urllib.request.html#urllib.request.getproxies" title="urllib.request.getproxies"><code class="xref py py-func docutils literal notranslate">getproxies()</code></a>.
</div>
</div>
<div class="section" id="sockets-and-layers">
<h2>Sockets and Layers<a class="headerlink" href="#sockets-and-layers" title="Permalink to this headline">¶</a></h2>
The Python support for fetching resources from the web is layered. urllib uses
the <a class="reference internal" href="../library/http.client.html#module-http.client" title="http.client: HTTP and HTTPS protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate">http.client</code></a> 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
<div class="highlight-python3 notranslate"><div class="highlight"><pre>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(&#39;http://www.voidspace.org.uk&#39;)
response = urllib.request.urlopen(req)
</pre></div>
</div>
</div>
<hr class="docutils" />
<div class="section" id="footnotes">
<h2>Footnotes<a class="headerlink" href="#footnotes" title="Permalink to this headline">¶</a></h2>
This document was reviewed and revised by John Lee.
<table class="docutils footnote" frame="void" id="id8" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>Google for example.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id9" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id2">[2]</a></td><td>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.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id10" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id3">[3]</a></td><td>The user agent for MSIE 6 is
‘Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)’</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id11" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id4">[4]</a></td><td>For details of more HTTP request headers, see
<a class="reference external" href="https://www.cs.tut.fi/~jkorpela/http.html">Quick Reference to HTTP Headers</a>.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id12" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id6">[5]</a></td><td>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.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id13" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id7">[6]</a></td><td>urllib opener for SSL proxy (CONNECT method): <a class="reference external" href="https://code.activestate.com/recipes/456195/">ASPN Cookbook Recipe</a>.</td></tr>
</tbody>
</table>
</div>
</div>

</div>
 </div>
 </div>
 <div class="sphinxsidebar" role="navigation" aria-label="main navigation">
 <div class="sphinxsidebarwrapper">
 <h3><a href="../contents.html">Table Of Contents</a></h3>
 <ul>
<li><a class="reference internal" href="#">HOWTO Fetch Internet Resources Using The urllib Package</a><ul>
<li><a class="reference internal" href="#introduction">Introduction</a></li>
<li><a class="reference internal" href="#fetching-urls">Fetching URLs</a><ul>
<li><a class="reference internal" href="#data">Data</a></li>
<li><a class="reference internal" href="#headers">Headers</a></li>
</ul>
</li>
<li><a class="reference internal" href="#handling-exceptions">Handling Exceptions</a><ul>
<li><a class="reference internal" href="#urlerror">URLError</a></li>
<li><a class="reference internal" href="#httperror">HTTPError</a><ul>
<li><a class="reference internal" href="#error-codes">Error Codes</a></li>
</ul>
</li>
<li><a class="reference internal" href="#wrapping-it-up">Wrapping it Up</a><ul>
<li><a class="reference internal" href="#number-1">Number 1</a></li>
<li><a class="reference internal" href="#number-2">Number 2</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#info-and-geturl">info and geturl</a></li>
<li><a class="reference internal" href="#openers-and-handlers">Openers and Handlers</a></li>
<li><a class="reference internal" href="#id5">Basic Authentication</a></li>
<li><a class="reference internal" href="#proxies">Proxies</a></li>
<li><a class="reference internal" href="#sockets-and-layers">Sockets and Layers</a></li>
<li><a class="reference internal" href="#footnotes">Footnotes</a></li>
</ul>
</li>
</ul>

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