132 lines
5.0 KiB
TeX
132 lines
5.0 KiB
TeX
\section{Standard Module \sectcode{urllib}}
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\stmodindex{urllib}
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\index{WWW}
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\index{World-Wide Web}
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\index{URL}
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\renewcommand{\indexsubitem}{(in module urllib)}
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This module provides a high-level interface for fetching data across
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the World-Wide Web. In particular, the \code{urlopen} function is
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similar to the built-in function \code{open}, but accepts URLs
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(Universal Resource Locators) instead of filenames. Some restrictions
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apply --- it can only open URLs for reading, and no seek operations
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are available.
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it defines the following public functions:
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\begin{funcdesc}{urlopen}{url}
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Open a network object denoted by a URL for reading. If the URL does
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not have a scheme identifier, or if it has \samp{file:} as its scheme
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identifier, this opens a local file; otherwise it opens a socket to a
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server somewhere on the network. If the connection cannot be made, or
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if the server returns an error code, the \code{IOError} exception is
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raised. If all went well, a file-like object is returned. This
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supports the following methods: \code{read()}, \code{readline()},
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\code{readlines()}, \code{fileno()}, \code{close()} and \code{info()}.
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Except for the last one, these methods have the same interface as for
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file objects --- see the section on File Objects earlier in this
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manual. (It's not a built-in file object, however, so it can't be
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used at those few places where a true built-in file object is
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required.)
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The \code{info()} method returns an instance of the class
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\code{rfc822.Message} containing the headers received from the server,
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if the protocol uses such headers (currently the only supported
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protocol that uses this is HTTP). See the description of the
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\code{rfc822} module.
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\end{funcdesc}
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\begin{funcdesc}{urlretrieve}{url}
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Copy a network object denoted by a URL to a local file, if necessary.
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If the URL points to a local file, or a valid cached copy of the
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object exists, the object is not copied. Return a tuple (\var{filename},
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\var{headers}) where \var{filename} is the local file name under which
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the object can be found, and \var{headers} is either \code{None} (for
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a local object) or whatever the \code{info()} method of the object
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returned by \code{urlopen()} returned (for a remote object, possibly
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cached). Exceptions are the same as for \code{urlopen()}.
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\end{funcdesc}
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\begin{funcdesc}{urlcleanup}{}
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Clear the cache that may have been built up by previous calls to
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\code{urlretrieve()}.
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\end{funcdesc}
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\begin{funcdesc}{quote}{string\optional{\, addsafe}}
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Replace special characters in \var{string} using the \code{\%xx} escape.
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Letters, digits, and the characters ``\code{_,.-}'' are never quoted.
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The optional \var{addsafe} parameter specifies additional characters
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that should not be quoted --- its default value is \code{'/'}.
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Example: \code{quote('/\~connolly/')} yields \code{'/\%7econnolly/'}.
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\end{funcdesc}
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\begin{funcdesc}{quote_plus}{string\optional{\, addsafe}}
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Like \code{quote()}, but also replaces spaces by plus signs, as
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required for quoting HTML form values.
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\end{funcdesc}
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\begin{funcdesc}{unquote}{string}
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Replace \samp{\%xx} escapes by their single-character equivalent.
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Example: \code{unquote('/\%7Econnolly/')} yields \code{'/\~connolly/'}.
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\end{funcdesc}
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\begin{funcdesc}{unquote_plus}{string}
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Like \code{unquote()}, but also replaces plus signs by spaces, as
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required for unquoting HTML form values.
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\end{funcdesc}
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Restrictions:
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\begin{itemize}
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\item
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Currently, only the following protocols are supported: HTTP, (versions
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0.9 and 1.0), Gopher (but not Gopher-+), FTP, and local files.
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\index{HTTP}
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\index{Gopher}
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\index{FTP}
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\item
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The caching feature of \code{urlretrieve()} has been disabled until I
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find the time to hack proper processing of Expiration time headers.
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\item
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There should be a function to query whether a particular URL is in
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the cache.
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\item
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For backward compatibility, if a URL appears to point to a local file
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but the file can't be opened, the URL is re-interpreted using the FTP
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protocol. This can sometimes cause confusing error messages.
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\item
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The \code{urlopen()} and \code{urlretrieve()} functions can cause
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arbitrarily long delays while waiting for a network connection to be
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set up. This means that it is difficult to build an interactive
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web client using these functions without using threads.
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\item
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The data returned by \code{urlopen()} or \code{urlretrieve()} is the
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raw data returned by the server. This may be binary data (e.g. an
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image), plain text or (for example) HTML. The HTTP protocol provides
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type information in the reply header, which can be inspected by
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looking at the \code{Content-type} header. For the Gopher protocol,
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type information is encoded in the URL; there is currently no easy way
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to extract it. If the returned data is HTML, you can use the module
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\code{htmllib} to parse it.
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\index{HTML}
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\index{HTTP}
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\index{Gopher}
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\stmodindex{htmllib}
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\item
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Although the \code{urllib} module contains (undocumented) routines to
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parse and unparse URL strings, the recommended interface for URL
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manipulation is in module \code{urlparse}.
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\stmodindex{urlparse}
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\end{itemize}
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