167 lines
6.2 KiB
TeX
167 lines
6.2 KiB
TeX
\section{\module{multifile} ---
|
|
Support for files containing distinct parts}
|
|
|
|
\declaremodule{standard}{multifile}
|
|
\modulesynopsis{Support for reading files which contain distinct
|
|
parts, such as some MIME data.}
|
|
\sectionauthor{Eric S. Raymond}{esr@snark.thyrsus.com}
|
|
|
|
|
|
The \class{MultiFile} object enables you to treat sections of a text
|
|
file as file-like input objects, with \code{''} being returned by
|
|
\method{readline()} when a given delimiter pattern is encountered. The
|
|
defaults of this class are designed to make it useful for parsing
|
|
MIME multipart messages, but by subclassing it and overriding methods
|
|
it can be easily adapted for more general use.
|
|
|
|
\begin{classdesc}{MultiFile}{fp\optional{, seekable}}
|
|
Create a multi-file. You must instantiate this class with an input
|
|
object argument for the \class{MultiFile} instance to get lines from,
|
|
such as as a file object returned by \function{open()}.
|
|
|
|
\class{MultiFile} only ever looks at the input object's
|
|
\method{readline()}, \method{seek()} and \method{tell()} methods, and
|
|
the latter two are only needed if you want random access to the
|
|
individual MIME parts. To use \class{MultiFile} on a non-seekable
|
|
stream object, set the optional \var{seekable} argument to false; this
|
|
will prevent using the input object's \method{seek()} and
|
|
\method{tell()} methods.
|
|
\end{classdesc}
|
|
|
|
It will be useful to know that in \class{MultiFile}'s view of the world, text
|
|
is composed of three kinds of lines: data, section-dividers, and
|
|
end-markers. MultiFile is designed to support parsing of
|
|
messages that may have multiple nested message parts, each with its
|
|
own pattern for section-divider and end-marker lines.
|
|
|
|
|
|
\subsection{MultiFile Objects \label{MultiFile-objects}}
|
|
|
|
A \class{MultiFile} instance has the following methods:
|
|
|
|
\begin{methoddesc}{push}{str}
|
|
Push a boundary string. When an appropriately decorated version of
|
|
this boundary is found as an input line, it will be interpreted as a
|
|
section-divider or end-marker. All subsequent
|
|
reads will return the empty string to indicate end-of-file, until a
|
|
call to \method{pop()} removes the boundary a or \method{next()} call
|
|
reenables it.
|
|
|
|
It is possible to push more than one boundary. Encountering the
|
|
most-recently-pushed boundary will return EOF; encountering any other
|
|
boundary will raise an error.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{readline}{str}
|
|
Read a line. If the line is data (not a section-divider or end-marker
|
|
or real EOF) return it. If the line matches the most-recently-stacked
|
|
boundary, return \code{''} and set \code{self.last} to 1 or 0 according as
|
|
the match is or is not an end-marker. If the line matches any other
|
|
stacked boundary, raise an error. On encountering end-of-file on the
|
|
underlying stream object, the method raises \exception{Error} unless
|
|
all boundaries have been popped.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{readlines}{str}
|
|
Return all lines remaining in this part as a list of strings.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{read}{}
|
|
Read all lines, up to the next section. Return them as a single
|
|
(multiline) string. Note that this doesn't take a size argument!
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{next}{}
|
|
Skip lines to the next section (that is, read lines until a
|
|
section-divider or end-marker has been consumed). Return true if
|
|
there is such a section, false if an end-marker is seen. Re-enable
|
|
the most-recently-pushed boundary.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{pop}{}
|
|
Pop a section boundary. This boundary will no longer be interpreted
|
|
as EOF.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{seek}{pos\optional{, whence}}
|
|
Seek. Seek indices are relative to the start of the current section.
|
|
The \var{pos} and \var{whence} arguments are interpreted as for a file
|
|
seek.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{tell}{}
|
|
Return the file position relative to the start of the current section.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{is_data}{str}
|
|
Return true if \var{str} is data and false if it might be a section
|
|
boundary. As written, it tests for a prefix other than \code{'-}\code{-'} at
|
|
start of line (which all MIME boundaries have) but it is declared so
|
|
it can be overridden in derived classes.
|
|
|
|
Note that this test is used intended as a fast guard for the real
|
|
boundary tests; if it always returns false it will merely slow
|
|
processing, not cause it to fail.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{section_divider}{str}
|
|
Turn a boundary into a section-divider line. By default, this
|
|
method prepends \code{'-}\code{-'} (which MIME section boundaries have) but
|
|
it is declared so it can be overridden in derived classes. This
|
|
method need not append LF or CR-LF, as comparison with the result
|
|
ignores trailing whitespace.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}{end_marker}{str}
|
|
Turn a boundary string into an end-marker line. By default, this
|
|
method prepends \code{'-}\code{-'} and appends \code{'-}\code{-'} (like a
|
|
MIME-multipart end-of-message marker) but it is declared so it can be
|
|
be overridden in derived classes. This method need not append LF or
|
|
CR-LF, as comparison with the result ignores trailing whitespace.
|
|
\end{methoddesc}
|
|
|
|
Finally, \class{MultiFile} instances have two public instance variables:
|
|
|
|
\begin{memberdesc}{level}
|
|
Nesting depth of the current part.
|
|
\end{memberdesc}
|
|
|
|
\begin{memberdesc}{last}
|
|
True if the last end-of-file was for an end-of-message marker.
|
|
\end{memberdesc}
|
|
|
|
|
|
\subsection{\class{MultiFile} Example \label{multifile-example}}
|
|
\sectionauthor{Skip Montanaro}{skip@mojam.com}
|
|
|
|
\begin{verbatim}
|
|
import mimetools
|
|
import MultiFile
|
|
import StringIO
|
|
|
|
def extract_mime_part_matching(stream, mimetype):
|
|
"""Return the first element in a multipart MIME message on stream
|
|
matching mimetype."""
|
|
|
|
msg = mimetools.Message(stream)
|
|
msgtype = msg.gettype()
|
|
params = msg.getplist()
|
|
|
|
data = StringIO.StringIO()
|
|
if msgtype[:10] == "multipart/":
|
|
|
|
file = multifile.MultiFile(stream)
|
|
file.push(msg.getparam("boundary"))
|
|
while file.next():
|
|
submsg = mimetools.Message(file)
|
|
try:
|
|
data = StringIO.StringIO()
|
|
mimetools.decode(file, data, submsg.getencoding())
|
|
except ValueError:
|
|
continue
|
|
if submsg.gettype() == mimetype:
|
|
break
|
|
file.pop()
|
|
return data.getvalue()
|
|
\end{verbatim}
|