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:
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:
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: timeout was added.
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:
The handlers raise this exception (or derived exceptions) when they run into a problem. It is a subclass of IOError.
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.
The following classes are provided:
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.
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 . 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.
The following methods describe all of Request‘s public interface, and so all must be overridden in subclasses.
Add a header that will not be added to a redirected request.
New in version 2.4.
Return whether the instance has the named header (checks both regular and unredirected).
New in version 2.4.
OpenerDirector instances have the following methods:
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).
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: timeout was added.
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.
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:
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.
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.
(“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().
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().
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().
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().
(“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.
(“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().
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.
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.
New in version 2.4.
HTTPCookieProcessor instances have one attribute:
(“protocol” is to be replaced by the protocol name.)
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.
These methods are available on HTTPPasswordMgr and HTTPPasswordMgrWithDefaultRealm objects.
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.
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).
CacheFTPHandler objects are FTPHandler objects with the following additional methods:
New in version 2.4.
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 protocol_error_code handler methods, via OpenerDirector.error(). Eventually, urllib2.HTTPDefaultErrorHandler will raise an HTTPError if no other handler handles the error.
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 User-Agent 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 (Content-Length, Content-Type and Host) are added when the Request is passed to urlopen() (or OpenerDirector.open()).