20.6. urllib2 — extensible library for opening URLs
Note
The urllib2 module has been split across several modules in
Python 3.0 named urllib.request and urllib.error.
The 2to3 tool will automatically adapt imports when converting
your sources to 3.0.
The urllib2 module defines functions and classes which help in opening
URLs (mostly HTTP) in a complex world — basic and digest authentication,
redirections, cookies and more.
The urllib2 module defines the following functions:
-
urllib2.urlopen(url[, data][, timeout])
Open the URL url, which can be either a string or a Request object.
data may be a string 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 HTTP request will be a POST instead of a GET when the
data parameter is provided. data should be a buffer in the standard
application/x-www-form-urlencoded format. The
urllib.urlencode() function takes a mapping or sequence of 2-tuples and
returns a string in this format.
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,
FTP and FTPS connections.
This function returns a file-like object with two additional methods:
geturl() — return the URL of the resource retrieved, commonly used to
determine if a redirect was followedinfo() — return the meta-information of the page, such as headers,
in the form of an mimetools.Message instance
(see Quick Reference to HTTP Headers)
Raises URLError on errors.
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, default installed ProxyHandler makes sure the requests
are handled through the proxy when they are set.
Changed in version 2.6:
Changed in version 2.6: timeout was added.
-
urllib2.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.
-
urllib2.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,
UnknownHandler, HTTPHandler, HTTPDefaultErrorHandler,
HTTPRedirectHandler, FTPHandler, FileHandler,
HTTPErrorProcessor.
If the Python installation has SSL support (i.e., if the ssl module can be imported),
HTTPSHandler will also be added.
Beginning in Python 2.3, a BaseHandler subclass may also change its
handler_order member variable to modify its position in the handlers
list.
The following exceptions are raised as appropriate:
-
exception
urllib2.URLError
The handlers raise this exception (or derived exceptions) when they run into a
problem. It is a subclass of IOError.
-
reason
The reason for this error. It can be a message string or another exception
instance (socket.error for remote URLs, OSError for local
URLs).
-
exception
urllib2.HTTPError
Though being an exception (a subclass of URLError), an HTTPError
can also function as a non-exceptional file-like return value (the same thing
that urlopen() returns). This is useful when handling exotic HTTP
errors, such as requests for authentication.
-
code
An HTTP status code as defined in RFC 2616.
This numeric value corresponds to a value found in the dictionary of
codes as found in BaseHTTPServer.BaseHTTPRequestHandler.responses.
The following classes are provided:
-
class
urllib2.Request(url[, data][, headers][, origin_req_host][, unverifiable])
This class is an abstraction of a URL request.
url should be a string containing a valid URL.
data may be a string 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 HTTP request will be a POST instead of a GET when the
data parameter is provided. data should be a buffer in the standard
application/x-www-form-urlencoded format. The
urllib.urlencode() function takes a mapping or sequence of 2-tuples and
returns a string in this format.
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, 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 urllib2‘s
default user agent string is "Python-urllib/2.6" (on Python 2.6).
The final 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 cookielib.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.
-
class
urllib2.OpenerDirector
The OpenerDirector class opens URLs via BaseHandlers chained
together. It manages the chaining of handlers, and recovery from errors.
-
class
urllib2.BaseHandler
This is the base class for all registered handlers — and handles only the
simple mechanics of registration.
-
class
urllib2.HTTPDefaultErrorHandler
A class which defines a default handler for HTTP error responses; all responses
are turned into HTTPError exceptions.
-
class
urllib2.HTTPRedirectHandler
A class to handle redirections.
-
class
urllib2.HTTPCookieProcessor([cookiejar])
A class to handle HTTP Cookies.
-
class
urllib2.ProxyHandler([proxies])
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, 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.
-
class
urllib2.HTTPPasswordMgr
Keep a database of (realm, uri) -> (user, password) mappings.
-
class
urllib2.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
urllib2.AbstractBasicAuthHandler([password_mgr])
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 Objects for information on the interface that must be
supported.
-
class
urllib2.HTTPBasicAuthHandler([password_mgr])
Handle authentication with the remote host. password_mgr, if given, should be
something that is compatible with HTTPPasswordMgr; refer to section
HTTPPasswordMgr Objects for information on the interface that must be
supported.
-
class
urllib2.ProxyBasicAuthHandler([password_mgr])
Handle authentication with the proxy. password_mgr, if given, should be
something that is compatible with HTTPPasswordMgr; refer to section
HTTPPasswordMgr Objects for information on the interface that must be
supported.
-
class
urllib2.AbstractDigestAuthHandler([password_mgr])
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 Objects for information on the interface that must be
supported.
-
class
urllib2.HTTPDigestAuthHandler([password_mgr])
Handle authentication with the remote host. password_mgr, if given, should be
something that is compatible with HTTPPasswordMgr; refer to section
HTTPPasswordMgr Objects for information on the interface that must be
supported.
-
class
urllib2.ProxyDigestAuthHandler([password_mgr])
Handle authentication with the proxy. password_mgr, if given, should be
something that is compatible with HTTPPasswordMgr; refer to section
HTTPPasswordMgr Objects for information on the interface that must be
supported.
-
class
urllib2.HTTPHandler
A class to handle opening of HTTP URLs.
-
class
urllib2.HTTPSHandler
A class to handle opening of HTTPS URLs.
-
class
urllib2.FileHandler
Open local files.
-
class
urllib2.FTPHandler
Open FTP URLs.
-
class
urllib2.CacheFTPHandler
Open FTP URLs, keeping a cache of open FTP connections to minimize delays.
-
class
urllib2.UnknownHandler
A catch-all class to handle unknown URLs.
20.6.1. Request Objects
The following methods describe all of Request‘s public interface, and
so all must be overridden in subclasses.
-
Request.add_data(data)
Set the Request data to data. This is ignored by all handlers except
HTTP handlers — and there it should be a byte string, and will change the
request to be POST rather than GET.
-
Request.get_method()
Return a string indicating the HTTP request method. This is only meaningful for
HTTP requests, and currently always returns 'GET' or 'POST'.
-
Request.has_data()
Return whether the instance has a non-None data.
-
Request.get_data()
Return the instance’s data.
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.
Add a header that will not be added to a redirected request.
New in version 2.4:
New in version 2.4.
Return whether the instance has the named header (checks both regular and
unredirected).
New in version 2.4:
New in version 2.4.
-
Request.get_full_url()
Return the URL given in the constructor.
-
Request.get_type()
Return the type of the URL — also known as the scheme.
-
Request.get_host()
Return the host to which a connection will be made.
-
Request.get_selector()
Return the selector — the part of the URL that is sent to the server.
-
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_origin_req_host()
Return the request-host of the origin transaction, as defined by RFC 2965.
See the documentation for the Request constructor.
-
Request.is_unverifiable()
Return whether the request is unverifiable, as defined by RFC 2965. See the
documentation for the Request constructor.
20.6.2. OpenerDirector Objects
OpenerDirector instances have the following methods:
-
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).
protocol_open — signal that the handler knows how to open
protocol URLs.http_error_type — signal that the handler knows how to handle
HTTP errors with HTTP error code type.protocol_error — signal that the handler knows how to handle
errors from (non-http) protocol.protocol_request — signal that the handler knows how to
pre-process protocol requests.protocol_response — signal that the handler knows how to
post-process protocol responses.
-
OpenerDirector.open(url[, data][, 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, FTP and FTPS connections).
Changed in version 2.6:
Changed in version 2.6: timeout was added.
-
OpenerDirector.error(proto[, arg[, ...]])
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_*()
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.
Every handler with a method named like protocol_request has that
method called to pre-process the request.
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.
Every handler with a method named like protocol_response has that
method called to post-process the response.
20.6.3. BaseHandler Objects
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 members and methods should only be used by classes derived from
BaseHandler.
Note
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)
(“protocol” is to be replaced by the protocol name.)
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)
(“protocol” is to be replaced by the protocol name.)
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)
(“protocol” is to be replaced by the protocol name.)
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().
20.6.4. HTTPRedirectHandler Objects
Note
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.
-
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.
Note
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.
20.6.5. HTTPCookieProcessor Objects
New in version 2.4:
New in version 2.4.
HTTPCookieProcessor instances have one attribute:
-
HTTPCookieProcessor.cookiejar
The cookielib.CookieJar in which cookies are stored.
20.6.21. Examples
This example gets the python.org main page and displays the first 100 bytes of
it:
>>> import urllib2
>>> f = urllib2.urlopen('http://www.python.org/')
>>> print f.read(100)
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<?xml-stylesheet href="./css/ht2html
Here 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 urllib2
>>> req = urllib2.Request(url='https://localhost/cgi-bin/test.cgi',
... data='This data is passed to stdin of the CGI')
>>> f = urllib2.urlopen(req)
>>> print f.read()
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
Use of Basic HTTP Authentication:
import urllib2
# Create an OpenerDirector with support for Basic HTTP Authentication...
auth_handler = urllib2.HTTPBasicAuthHandler()
auth_handler.add_password(realm='PDQ Application',
uri='https://mahler:8092/site-updates.py',
user='klem',
passwd='kadidd!ehopper')
opener = urllib2.build_opener(auth_handler)
# ...and install it globally so it can be used with urlopen.
urllib2.install_opener(opener)
urllib2.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 = urllib2.ProxyHandler({'http': 'http://www.example.com:3128/'})
proxy_auth_handler = urllib2.ProxyBasicAuthHandler()
proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
opener = urllib2.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 urllib2
req = urllib2.Request('http://www.example.com/')
req.add_header('Referer', 'http://www.python.org/')
r = urllib2.urlopen(req)
OpenerDirector automatically adds a header to
every Request. To change this:
import urllib2
opener = urllib2.build_opener()
opener.addheaders = [('User-agent', 'Mozilla/5.0')]
opener.open('http://www.example.com/')
Also, remember that a few standard headers (,
and ) are added when the
Request is passed to urlopen() (or OpenerDirector.open()).