114 lines
5.1 KiB
TeX
114 lines
5.1 KiB
TeX
\declaremodule{standard}{email.Parser}
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\modulesynopsis{Parse flat text email messages to produce a message
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object tree.}
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Message object trees can be created in one of two ways: they can be
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created from whole cloth by instantiating \class{Message} objects and
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stringing them together via \method{add_payload()} and
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\method{set_payload()} calls, or they can be created by parsing a flat text
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representation of the email message.
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The \module{email} package provides a standard parser that understands
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most email document structures, including MIME documents. You can
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pass the parser a string or a file object, and the parser will return
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to you the root \class{Message} instance of the object tree. For
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simple, non-MIME messages the payload of this root object will likely
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be a string containing the text of the message. For MIME
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messages, the root object will return true from its
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\method{is_multipart()} method, and the subparts can be accessed via
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the \method{get_payload()} and \method{walk()} methods.
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Note that the parser can be extended in limited ways, and of course
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you can implement your own parser completely from scratch. There is
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no magical connection between the \module{email} package's bundled
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parser and the \class{Message} class, so your custom parser can create
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message object trees any way it finds necessary.
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The primary parser class is \class{Parser} which parses both the
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headers and the payload of the message. In the case of
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\mimetype{multipart} messages, it will recursively parse the body of
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the container message. The \module{email.Parser} module also provides
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a second class, called \class{HeaderParser} which can be used if
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you're only interested in the headers of the message.
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\class{HeaderParser} can be much faster in this situations, since it
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does not attempt to parse the message body, instead setting the
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payload to the raw body as a string. \class{HeaderParser} has the
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same API as the \class{Parser} class.
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\subsubsection{Parser class API}
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\begin{classdesc}{Parser}{\optional{_class}}
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The constructor for the \class{Parser} class takes a single optional
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argument \var{_class}. This must be a callable factory (such as a
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function or a class), and it is used whenever a sub-message object
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needs to be created. It defaults to \class{Message} (see
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\refmodule{email.Message}). The factory will be called without
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arguments.
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\end{classdesc}
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The other public \class{Parser} methods are:
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\begin{methoddesc}[Parser]{parse}{fp}
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Read all the data from the file-like object \var{fp}, parse the
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resulting text, and return the root message object. \var{fp} must
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support both the \method{readline()} and the \method{read()} methods
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on file-like objects.
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The text contained in \var{fp} must be formatted as a block of \rfc{2822}
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style headers and header continuation lines, optionally preceeded by a
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\emph{Unix-From} header. The header block is terminated either by the
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end of the data or by a blank line. Following the header block is the
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body of the message (which may contain MIME-encoded subparts).
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\end{methoddesc}
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\begin{methoddesc}[Parser]{parsestr}{text}
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Similar to the \method{parse()} method, except it takes a string
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object instead of a file-like object. Calling this method on a string
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is exactly equivalent to wrapping \var{text} in a \class{StringIO}
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instance first and calling \method{parse()}.
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\end{methoddesc}
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Since creating a message object tree from a string or a file object is
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such a common task, two functions are provided as a convenience. They
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are available in the top-level \module{email} package namespace.
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\begin{funcdesc}{message_from_string}{s\optional{, _class}}
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Return a message object tree from a string. This is exactly
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equivalent to \code{Parser().parsestr(s)}. Optional \var{_class} is
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interpreted as with the \class{Parser} class constructor.
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\end{funcdesc}
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\begin{funcdesc}{message_from_file}{fp\optional{, _class}}
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Return a message object tree from an open file object. This is exactly
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equivalent to \code{Parser().parse(fp)}. Optional \var{_class} is
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interpreted as with the \class{Parser} class constructor.
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\end{funcdesc}
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Here's an example of how you might use this at an interactive Python
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prompt:
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\begin{verbatim}
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>>> import email
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>>> msg = email.message_from_string(myString)
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\end{verbatim}
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\subsubsection{Additional notes}
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Here are some notes on the parsing semantics:
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\begin{itemize}
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\item Most non-\mimetype{multipart} type messages are parsed as a single
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message object with a string payload. These objects will return
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0 for \method{is_multipart()}.
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\item One exception is for \mimetype{message/delivery-status} type
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messages. Because the body of such messages consist of
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blocks of headers, \class{Parser} will create a non-multipart
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object containing non-multipart subobjects for each header
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block.
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\item Another exception is for \mimetype{message/*} types (more
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general than \mimetype{message/delivery-status}). These are
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typically \mimetype{message/rfc822} messages, represented as a
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non-multipart object containing a singleton payload which is
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another non-multipart \class{Message} instance.
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\end{itemize}
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