\section{\module{urllib} ---         Open arbitrary resources by URL} \declaremodule{standard}{urllib}\modulesynopsis{Open an arbitrary network resource by URL (requires sockets).} \index{WWW}\index{World Wide Web}\index{URL}  This module provides a high-level interface for fetching data acrossthe World Wide Web.  In particular, the \function{urlopen()} functionis similar to the built-in function \function{open()}, but acceptsUniversal Resource Locators (URLs) instead of filenames.  Somerestrictions apply --- it can only open URLs for reading, and no seekoperations are available. It defines the following public functions: \begin{funcdesc}{urlopen}{url\optional{, data\optional{, proxies}}}Open a network object denoted by a URL for reading.  If the URL doesnot have a scheme identifier, or if it has \file{file:} as its schemeidentifier, this opens a local file (without universal newlines);otherwise it opens a socket to a server somewhere on the network.  Ifthe connection cannot be madethe \exception{IOError} exception is raised.  If all went well, afile-like object is returned.  This supports the following methods:\method{read()}, \method{readline()}, \method{readlines()}, \method{fileno()},\method{close()}, \method{info()} and \method{geturl()}.  It also hasproper support for the iterator protocol.One caveat: the \method{read()} method, if the size argument isomitted or negative, may not read until the end of the data stream;there is no good way to determine that the entire stream from a sockethas been read in the general case. Except for the \method{info()} and \method{geturl()} methods,these methods have the same interface as forfile objects --- see section \ref{bltin-file-objects} in thismanual.  (It is not a built-in file object, however, so it can't beused at those few places where a true built-in file object isrequired.) The \method{info()} method returns an instance of the class\class{mimetools.Message} containing meta-information associatedwith the URL.  When the method is HTTP, these headers are thosereturned by the server at the head of the retrieved HTML page(including Content-Length and Content-Type).  When the method is FTP,a Content-Length header will be present if (as is now usual) theserver passed back a file length in response to the FTP retrievalrequest. A Content-Type header will be present if the MIME type canbe guessed.  When the method is local-file, returned headers will includea Date representing the file's last-modified time, a Content-Lengthgiving file size, and a Content-Type containing a guess at the file'stype. See also the description of the\refmodule{mimetools}\refstmodindex{mimetools} module. The \method{geturl()} method returns the real URL of the page.  Insome cases, the HTTP server redirects a client to another URL.  The\function{urlopen()} function handles this transparently, but in somecases the caller needs to know which URL the client was redirectedto.  The \method{geturl()} method can be used to get at thisredirected URL. If the \var{url} uses the \file{http:} scheme identifier, the optional\var{data} argument may be given to specify a \code{POST} request(normally the request type is \code{GET}).  The \var{data} argumentmust be in standard \mimetype{application/x-www-form-urlencoded} format;see the \function{urlencode()} function below. The \function{urlopen()} function works transparently with proxieswhich do not require authentication.  In a \UNIX{} or Windowsenvironment, set the \envvar{http_proxy}, \envvar{ftp_proxy} or\envvar{gopher_proxy} environment variables to a URL that identifiesthe proxy server before starting the Python interpreter.  For example(the \character{\%} is the command prompt): \begin{verbatim}% http_proxy="http://www.someproxy.com:3128"% export http_proxy% python...\end{verbatim} In a Windows environment, if no proxy environment variables are set,proxy settings are obtained from the registry's Internet Settingssection. In a Macintosh environment, \function{urlopen()} will retrieve proxyinformation from Internet\index{Internet Config} Config. Alternatively, the optional \var{proxies} argument may be used toexplicitly specify proxies.  It must be a dictionary mapping schemenames to proxy URLs, where an empty dictionary causes no proxies to beused, and \code{None} (the default value) causes environmental proxysettings to be used as discussed above.  For example: \begin{verbatim}# Use http://www.someproxy.com:3128 for http proxyingproxies = {'http': 'http://www.someproxy.com:3128'}filehandle = urllib.urlopen(some_url, proxies=proxies)# Don't use any proxiesfilehandle = urllib.urlopen(some_url, proxies={})# Use proxies from environment - both versions are equivalentfilehandle = urllib.urlopen(some_url, proxies=None)filehandle = urllib.urlopen(some_url)\end{verbatim} The \function{urlopen()} function does not support explicit proxyspecification.  If you need to override environmental proxy settings,use \class{URLopener}, or a subclass such as \class{FancyURLopener}. Proxies which require authentication for use are not currentlysupported; this is considered an implementation limitation. \versionchanged[Added the \var{proxies} support]{2.3}\end{funcdesc} \begin{funcdesc}{urlretrieve}{url\optional{, filename\optional{,                              reporthook\optional{, data}}}}Copy a network object denoted by a URL to a local file, if necessary.If the URL points to a local file, or a valid cached copy of theobject exists, the object is not copied.  Return a tuple\code{(\var{filename}, \var{headers})} where \var{filename} is thelocal file name under which the object can be found, and \var{headers}is whatever the \method{info()} method of the object returned by\function{urlopen()} returned (for a remote object, possibly cached).Exceptions are the same as for \function{urlopen()}. The second argument, if present, specifies the file location to copyto (if absent, the location will be a tempfile with a generated name).The third argument, if present, is a hook function that will be calledonce on establishment of the network connection and once after eachblock read thereafter.  The hook will be passed three arguments; acount of blocks transferred so far, a block size in bytes, and thetotal size of the file.  The third argument may be \code{-1} on olderFTP servers which do not return a file size in response to a retrievalrequest. If the \var{url} uses the \file{http:} scheme identifier, the optional\var{data} argument may be given to specify a \code{POST} request(normally the request type is \code{GET}).  The \var{data} argumentmust in standard \mimetype{application/x-www-form-urlencoded} format;see the \function{urlencode()} function below. \versionchanged[\function{urlretrieve()} will raise \exception{ContentTooShortError}when it detects that the amount of data available was less than the expected amount (which is the size reported by a \var{Content-Length} header). This can occur, for example, when the download is interrupted. The \var{Content-Length} is treated as a lower bound: if there's more data to read, urlretrieve reads more data, but if less data is available, it raises the exception. You can still retrieve the downloaded data in this case, it is stored in the \member{content} attribute of the exception instance. If no \var{Content-Length} header was supplied, urlretrieve cannot check the size of the data it has downloaded, and just returns it. In this case you just have to assume that the download was successful]{2.5} \end{funcdesc} \begin{datadesc}{_urlopener}The public functions \function{urlopen()} and\function{urlretrieve()} create an instance of the\class{FancyURLopener} class and use it to perform their requestedactions.  To override this functionality, programmers can create asubclass of \class{URLopener} or \class{FancyURLopener}, then assignan instance of that class to the\code{urllib._urlopener} variable before calling the desired function.For example, applications may want to specify a different\mailheader{User-Agent} header than \class{URLopener} defines.  Thiscan be accomplished with the following code: \begin{verbatim}import urllib class AppURLopener(urllib.FancyURLopener):    version = "App/1.7" urllib._urlopener = AppURLopener()\end{verbatim}\end{datadesc} \begin{funcdesc}{urlcleanup}{}Clear the cache that may have been built up by previous calls to\function{urlretrieve()}.\end{funcdesc} \begin{funcdesc}{quote}{string\optional{, safe}}Replace special characters in \var{string} using the \samp{\%xx} escape.Letters, digits, and the characters \character{_.-} are never quoted.The optional \var{safe} parameter specifies additional charactersthat should not be quoted --- its default value is \code{'/'}. Example: \code{quote('/\~{}connolly/')} yields \code{'/\%7econnolly/'}.\end{funcdesc} \begin{funcdesc}{quote_plus}{string\optional{, safe}}Like \function{quote()}, but also replaces spaces by plus signs, asrequired for quoting HTML form values.  Plus signs in the originalstring are escaped unless they are included in \var{safe}.  It alsodoes not have \var{safe} default to \code{'/'}.\end{funcdesc} \begin{funcdesc}{unquote}{string}Replace \samp{\%xx} escapes by their single-character equivalent. Example: \code{unquote('/\%7Econnolly/')} yields \code{'/\~{}connolly/'}.\end{funcdesc} \begin{funcdesc}{unquote_plus}{string}Like \function{unquote()}, but also replaces plus signs by spaces, asrequired for unquoting HTML form values.\end{funcdesc} \begin{funcdesc}{urlencode}{query\optional{, doseq}}Convert a mapping object or a sequence of two-element tuples  to a``url-encoded'' string, suitable to pass to\function{urlopen()} above as the optional \var{data} argument.  Thisis useful to pass a dictionary of form fields to a \code{POST}request.  The resulting string is a series of\code{\var{key}=\var{value}} pairs separated by \character{\&}characters, where both \var{key} and \var{value} are quoted using\function{quote_plus()} above.  If the optional parameter \var{doseq} ispresent and evaluates to true, individual \code{\var{key}=\var{value}} pairsare generated for each element of the sequence.When a sequence of two-element tuples is used as the \var{query} argument,the first element of each tuple is a key and the second is a value.  Theorder of parameters in the encoded string will match the order of parametertuples in the sequence.The \refmodule{cgi} module provides the functions\function{parse_qs()} and \function{parse_qsl()} which are used toparse query strings into Python data structures.\end{funcdesc} \begin{funcdesc}{pathname2url}{path}Convert the pathname \var{path} from the local syntax for a path tothe form used in the path component of a URL.  This does not produce acomplete URL.  The return value will already be quoted using the\function{quote()} function.\end{funcdesc} \begin{funcdesc}{url2pathname}{path}Convert the path component \var{path} from an encoded URL to the localsyntax for a path.  This does not accept a complete URL.  Thisfunction uses \function{unquote()} to decode \var{path}.\end{funcdesc} \begin{classdesc}{URLopener}{\optional{proxies\optional{, **x509}}}Base class for opening and reading URLs.  Unless you need to supportopening objects using schemes other than \file{http:}, \file{ftp:},\file{gopher:} or \file{file:}, you probably want to use\class{FancyURLopener}. By default, the \class{URLopener} class sends a\mailheader{User-Agent} header of \samp{urllib/\var{VVV}}, where\var{VVV} is the \module{urllib} version number.  Applications candefine their own \mailheader{User-Agent} header by subclassing\class{URLopener} or \class{FancyURLopener} and setting the classattribute \member{version} to an appropriate string value in thesubclass definition. The optional \var{proxies} parameter should be a dictionary mappingscheme names to proxy URLs, where an empty dictionary turns proxiesoff completely.  Its default value is \code{None}, in which caseenvironmental proxy settings will be used if present, as discussed inthe definition of \function{urlopen()}, above. Additional keyword parameters, collected in \var{x509}, may be used forauthentication of the client when using the \file{https:} scheme.  The keywords\var{key_file} and \var{cert_file} are supported to provide an SSL key and certificate; both are needed to support client authentication. \class{URLopener} objects will raise an \exception{IOError} exceptionif the server returns an error code.\end{classdesc} \begin{classdesc}{FancyURLopener}{...}\class{FancyURLopener} subclasses \class{URLopener} providing defaulthandling for the following HTTP response codes: 301, 302, 303, 307 and401.  For the 30x response codes listed above, the\mailheader{Location} header is used to fetch the actual URL.  For 401response codes (authentication required), basic HTTP authentication isperformed.  For the 30x response codes, recursion is bounded by thevalue of the \var{maxtries} attribute, which defaults to 10. For all other response codes, the method \method{http_error_default()}is called which you can override in subclasses to handle the errorappropriately. \note{According to the letter of \rfc{2616}, 301 and 302 responses to  POST requests must not be automatically redirected without  confirmation by the user.  In reality, browsers do allow automatic  redirection of these responses, changing the POST to a GET, and  \module{urllib} reproduces this behaviour.} The parameters to the constructor are the same as those for\class{URLopener}. \note{When performing basic authentication, a\class{FancyURLopener} instance calls its\method{prompt_user_passwd()} method.  The default implementation asksthe users for the required information on the controlling terminal.  Asubclass may override this method to support more appropriate behaviorif needed.}\end{classdesc} \begin{excclassdesc}{ContentTooShortError}{msg\optional{, content}}This exception is raised when the \function{urlretrieve()} functiondetects that the amount of the downloaded data is less than the expected amount (given by the \var{Content-Length} header). The\member{content} attribute stores the downloaded (and supposedlytruncated) data.\versionadded{2.5}\end{excclassdesc} Restrictions: \begin{itemize} \itemCurrently, only the following protocols are supported: HTTP, (versions0.9 and 1.0), Gopher (but not Gopher-+), FTP, and local files.\indexii{HTTP}{protocol}\indexii{Gopher}{protocol}\indexii{FTP}{protocol} \itemThe caching feature of \function{urlretrieve()} has been disableduntil I find the time to hack proper processing of Expiration timeheaders. \itemThere should be a function to query whether a particular URL is inthe cache. \itemFor backward compatibility, if a URL appears to point to a local filebut the file can't be opened, the URL is re-interpreted using the FTPprotocol.  This can sometimes cause confusing error messages. \itemThe \function{urlopen()} and \function{urlretrieve()} functions cancause arbitrarily long delays while waiting for a network connectionto be set up.  This means that it is difficult to build an interactiveWeb client using these functions without using threads. \itemThe data returned by \function{urlopen()} or \function{urlretrieve()}is the raw data returned by the server.  This may be binary data(such as an image), plain text or (for example) HTML\index{HTML}.  TheHTTP\indexii{HTTP}{protocol} protocol provides type information in thereply header, which can be inspected by looking at the\mailheader{Content-Type} header.  For theGopher\indexii{Gopher}{protocol} protocol, type information is encodedin the URL; there is currently no easy way to extract it.  If thereturned data is HTML, you can use the module\refmodule{htmllib}\refstmodindex{htmllib} to parse it. \itemThe code handling the FTP\index{FTP} protocol cannot differentiatebetween a file and a directory.  This can lead to unexpected behaviorwhen attempting to read a URL that points to a file that is notaccessible.  If the URL ends in a \code{/}, it is assumed to refer toa directory and will be handled accordingly.  But if an attempt toread a file leads to a 550 error (meaning the URL cannot be found oris not accessible, often for permission reasons), then the path istreated as a directory in order to handle the case when a directory isspecified by a URL but the trailing \code{/} has been left off.  This cancause misleading results when you try to fetch a file whose readpermissions make it inaccessible; the FTP code will try to read it,fail with a 550 error, and then perform a directory listing for theunreadable file. If fine-grained control is needed, consider using the\module{ftplib} module, subclassing \class{FancyURLOpener}, or changing\var{_urlopener} to meet your needs. \itemThis module does not support the use of proxies which requireauthentication.  This may be implemented in the future. \itemAlthough the \module{urllib} module contains (undocumented) routinesto parse and unparse URL strings, the recommended interface for URLmanipulation is in module \refmodule{urlparse}\refstmodindex{urlparse}. \end{itemize}  \subsection{URLopener Objects \label{urlopener-objs}}\sectionauthor{Skip Montanaro}{skip@mojam.com} \class{URLopener} and \class{FancyURLopener} objects have thefollowing attributes. \begin{methoddesc}[URLopener]{open}{fullurl\optional{, data}}Open \var{fullurl} using the appropriate protocol.  This method setsup cache and proxy information, then calls the appropriate open method withits input arguments.  If the scheme is not recognized,\method{open_unknown()} is called.  The \var{data} argumenthas the same meaning as the \var{data} argument of \function{urlopen()}.\end{methoddesc} \begin{methoddesc}[URLopener]{open_unknown}{fullurl\optional{, data}}Overridable interface to open unknown URL types.\end{methoddesc} \begin{methoddesc}[URLopener]{retrieve}{url\optional{,                                        filename\optional{,                                        reporthook\optional{, data}}}}Retrieves the contents of \var{url} and places it in \var{filename}.  Thereturn value is a tuple consisting of a local filename and either a\class{mimetools.Message} object containing the response headers (for remoteURLs) or \code{None} (for local URLs).  The caller must then open and read thecontents of \var{filename}.  If \var{filename} is not given and the URLrefers to a local file, the input filename is returned.  If the URL isnon-local and \var{filename} is not given, the filename is the output of\function{tempfile.mktemp()} with a suffix that matches the suffix of the lastpath component of the input URL.  If \var{reporthook} is given, it must bea function accepting three numeric parameters.  It will be called after eachchunk of data is read from the network.  \var{reporthook} is ignored forlocal URLs. If the \var{url} uses the \file{http:} scheme identifier, the optional\var{data} argument may be given to specify a \code{POST} request(normally the request type is \code{GET}).  The \var{data} argumentmust in standard \mimetype{application/x-www-form-urlencoded} format;see the \function{urlencode()} function below.\end{methoddesc} \begin{memberdesc}[URLopener]{version}Variable that specifies the user agent of the opener object.  To get\refmodule{urllib} to tell servers that it is a particular user agent,set this in a subclass as a class variable or in the constructorbefore calling the base constructor.\end{memberdesc} The \class{FancyURLopener} class offers one additional method thatshould be overloaded to provide the appropriate behavior: \begin{methoddesc}[FancyURLopener]{prompt_user_passwd}{host, realm}Return information needed to authenticate the user at the given hostin the specified security realm.  The return value should be a tuple,\code{(\var{user}, \var{password})}, which can be used for basicauthentication. The implementation prompts for this information on the terminal; anapplication should override this method to use an appropriateinteraction model in the local environment.\end{methoddesc}  \subsection{Examples}\nodename{Urllib Examples} Here is an example session that uses the \samp{GET} method to retrievea URL containing parameters: \begin{verbatim}>>> import urllib>>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})>>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query?%s" % params)>>> print f.read()\end{verbatim} The following example uses the \samp{POST} method instead: \begin{verbatim}>>> import urllib>>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})>>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query", params)>>> print f.read()\end{verbatim} The following example uses an explicitly specified HTTP proxy,overriding environment settings: \begin{verbatim}>>> import urllib>>> proxies = {'http': 'http://proxy.example.com:8080/'}>>> opener = urllib.FancyURLopener(proxies)>>> f = opener.open("http://www.python.org")>>> f.read()\end{verbatim} The following example uses no proxies at all, overriding environmentsettings: \begin{verbatim}>>> import urllib>>> opener = urllib.FancyURLopener({})>>> f = opener.open("http://www.python.org/")>>> f.read()\end{verbatim}