\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 across the World Wide Web. In particular, the \function{urlopen()} function is similar to the built-in function \function{open()}, but accepts Universal Resource Locators (URLs) instead of filenames. Some restrictions apply --- it can only open URLs for reading, and no seek operations 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 does not have a scheme identifier, or if it has \file{file:} as its scheme identifier, this opens a local file; otherwise it opens a socket to a server somewhere on the network. If the connection cannot be made, or if the server returns an error code, the \exception{IOError} exception is raised. If all went well, a file-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 has proper support for the iterator protocol. Except for the \method{info()} and \method{geturl()} methods, these methods have the same interface as for file objects --- see section \ref{bltin-file-objects} in this manual. (It is not a built-in file object, however, so it can't be used at those few places where a true built-in file object is required.) The \method{info()} method returns an instance of the class \class{mimetools.Message} containing meta-information associated with the URL. When the method is HTTP, these headers are those returned 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) the server passed back a file length in response to the FTP retrieval request. A Content-Type header will be present if the MIME type can be guessed. When the method is local-file, returned headers will include a Date representing the file's last-modified time, a Content-Length giving file size, and a Content-Type containing a guess at the file's type. See also the description of the \refmodule{mimetools}\refstmodindex{mimetools} module. The \method{geturl()} method returns the real URL of the page. In some cases, the HTTP server redirects a client to another URL. The \function{urlopen()} function handles this transparently, but in some cases the caller needs to know which URL the client was redirected to. The \method{geturl()} method can be used to get at this redirected 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} argument must in standard \mimetype{application/x-www-form-urlencoded} format; see the \function{urlencode()} function below. The \function{urlopen()} function works transparently with proxies which do not require authentication. In a \UNIX{} or Windows environment, set the \envvar{http_proxy}, \envvar{ftp_proxy} or \envvar{gopher_proxy} environment variables to a URL that identifies the 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 envvironment variables are set, proxy settings are obtained from the registry's Internet Settings section. In a Macintosh environment, \function{urlopen()} will retrieve proxy information from Internet\index{Internet Config} Config. Alternatively, the optional \var{proxies} argument may be used to explicitly specify proxies. It must be a dictionary mapping scheme names to proxy URLs, where an empty dictionary causes no proxies to be used, and \code{None} (the default value) causes environmental proxy settings to be used as discussed above. For example: \begin{verbatim} # Use http://www.someproxy.com:3128 for http proxying proxies = proxies={'http': 'http://www.someproxy.com:3128'} filehandle = urllib.urlopen(some_url, proxies=proxies) # Don't use any proxies filehandle = urllib.urlopen(some_url, proxies={}) # Use proxies from environment - both versions are equivalent filehandle = urllib.urlopen(some_url, proxies=None) filehandle = urllib.urlopen(some_url) \end{verbatim} The \function{urlopen()} function does not support explicit proxy specification. 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 currently supported; 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 the object exists, the object is not copied. Return a tuple \code{(\var{filename}, \var{headers})} where \var{filename} is the local file name under which the object can be found, and \var{headers} is either \code{None} (for a local object) or 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 copy to (if absent, the location will be a tempfile with a generated name). The third argument, if present, is a hook function that will be called once on establishment of the network connection and once after each block read thereafter. The hook will be passed three arguments; a count of blocks transferred so far, a block size in bytes, and the total size of the file. The third argument may be \code{-1} on older FTP servers which do not return a file size in response to a retrieval request. 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} argument must in standard \mimetype{application/x-www-form-urlencoded} format; see the \function{urlencode()} function below. \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 requested actions. To override this functionality, programmers can create a subclass of \class{URLopener} or \class{FancyURLopener}, then assign that an 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. This can be accomplished with the following code: \begin{verbatim} import urllib class AppURLopener(urllib.FancyURLopener): def __init__(self, *args): self.version = "App/1.7" urllib.FancyURLopener.__init__(self, *args) 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 characters that 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, as required for quoting HTML form values. Plus signs in the original string are escaped unless they are included in \var{safe}. \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, as required 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. This is 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} is present and evaluates to true, individual \code{\var{key}=\var{value}} pairs are 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. The order of parameters in the encoded string will match the order of parameter tuples in the sequence. \end{funcdesc} \begin{funcdesc}{pathname2url}{path} Convert the pathname \var{path} from the local syntax for a path to the form used in the path component of a URL. This does not produce a complete 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 local syntax for a path. This does not accept a complete URL. This function 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 support opening 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 can define their own \mailheader{User-Agent} header by subclassing \class{URLopener} or \class{FancyURLopener} and setting the instance attribute \member{version} to an appropriate string value before the \method{open()} method is called. The optional \var{proxies} parameter should be a dictionary mapping scheme names to proxy URLs, where an empty dictionary turns proxies off completely. Its default value is \code{None}, in which case environmental proxy settings will be used if present, as discussed in the definition of \function{urlopen()}, above. Additional keyword parameters, collected in \var{x509}, are used for authentication with the \file{https:} scheme. The keywords \var{key_file} and \var{cert_file} are supported; both are needed to actually retrieve a resource at an \file{https:} URL. \end{classdesc} \begin{classdesc}{FancyURLopener}{...} \class{FancyURLopener} subclasses \class{URLopener} providing default handling for the following HTTP response codes: 301, 302 or 401. For 301 and 302 response codes, the \mailheader{Location} header is used to fetch the actual URL. For 401 response codes (authentication required), basic HTTP authentication is performed. For 301 and 302 response codes, recursion is bounded by the value of the \var{maxtries} attribute, which defaults 10. 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 asks the users for the required information on the controlling terminal. A subclass may override this method to support more appropriate behavior if needed.} \end{classdesc} Restrictions: \begin{itemize} \item Currently, only the following protocols are supported: HTTP, (versions 0.9 and 1.0), Gopher (but not Gopher-+), FTP, and local files. \indexii{HTTP}{protocol} \indexii{Gopher}{protocol} \indexii{FTP}{protocol} \item The caching feature of \function{urlretrieve()} has been disabled until I find the time to hack proper processing of Expiration time headers. \item There should be a function to query whether a particular URL is in the cache. \item For backward compatibility, if a URL appears to point to a local file but the file can't be opened, the URL is re-interpreted using the FTP protocol. This can sometimes cause confusing error messages. \item The \function{urlopen()} and \function{urlretrieve()} functions can cause arbitrarily long delays while waiting for a network connection to be set up. This means that it is difficult to build an interactive Web client using these functions without using threads. \item The data returned by \function{urlopen()} or \function{urlretrieve()} is the raw data returned by the server. This may be binary data (e.g. an image), plain text or (for example) HTML\index{HTML}. The HTTP\indexii{HTTP}{protocol} protocol provides type information in the reply header, which can be inspected by looking at the \mailheader{Content-Type} header. For the Gopher\indexii{Gopher}{protocol} protocol, type information is encoded in the URL; there is currently no easy way to extract it. If the returned data is HTML, you can use the module \refmodule{htmllib}\refstmodindex{htmllib} to parse it. \item This module does not support the use of proxies which require authentication. This may be implemented in the future. \item Although the \module{urllib} module contains (undocumented) routines to parse and unparse URL strings, the recommended interface for URL manipulation 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 the following attributes. \begin{methoddesc}[URLopener]{open}{fullurl\optional{, data}} Open \var{fullurl} using the appropriate protocol. This method sets up cache and proxy information, then calls the appropriate open method with its input arguments. If the scheme is not recognized, \method{open_unknown()} is called. The \var{data} argument has 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}. The return value is a tuple consisting of a local filename and either a \class{mimetools.Message} object containing the response headers (for remote URLs) or \code{None} (for local URLs). The caller must then open and read the contents of \var{filename}. If \var{filename} is not given and the URL refers to a local file, the input filename is returned. If the URL is non-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 last path component of the input URL. If \var{reporthook} is given, it must be a function accepting three numeric parameters. It will be called after each chunk of data is read from the network. \var{reporthook} is ignored for local 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} argument must 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 constructor before calling the base constructor. \end{memberdesc} The \class{FancyURLopener} class offers one additional method that should 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 host in the specified security realm. The return value should be a tuple, \code{(\var{user}, \var{password})}, which can be used for basic authentication. The implementation prompts for this information on the terminal; an application should override this method to use an appropriate interaction model in the local environment. \end{methoddesc} \subsection{Examples} \nodename{Urllib Examples} Here is an example session that uses the \samp{GET} method to retrieve a 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 environment settings: \begin{verbatim} >>> import urllib >>> opener = urllib.FancyURLopener({}) >>> f = opener.open("http://www.python.org/") >>> f.read() \end{verbatim}