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  2. cpython-withatomic


cpython-withatomic / Doc / libmarshal.tex

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\section{Built-in Module \sectcode{marshal}}

This module contains functions that can read and write Python
values in a binary format.  The format is specific to Python, but
independent of machine architecture issues (e.g., you can write a
Python value to a file on a VAX, transport the file to a Mac, and read
it back there).  Details of the format not explained here; read the
source if you're interested.%
\footnote{The name of this module stems from a bit of terminology used
by the designers of Modula-3 (amongst others), who use the term
``marshalling'' for shipping of data around in a self-contained form.
Strictly speaking, ``to marshal'' means to convert some data from
internal to external form (in an RPC buffer for instance) and
``unmarshalling'' for the reverse process.}

Not all Python object types are supported; in general, only objects
whose value is independent from a particular invocation of Python can
be written and read by this module.  The following types are supported:
\code{None}, integers, long integers, floating point numbers,
strings, tuples, lists, dictionaries, and code objects, where it
should be understood that tuples, lists and dictionaries are only
supported as long as the values contained therein are themselves
supported; and recursive lists and dictionaries should not be written
(they will cause an infinite loop).

There are functions that read/write files as well as functions
operating on strings.

The module defines these functions:

\renewcommand{\indexsubitem}{(in module marshal)}
\begin{funcdesc}{dump}{value\, file}
  Write the value on the open file.  The value must be a supported
  type.  The file must be an open file object such as
  \code{sys.stdout} or returned by \code{open()} or
  If the value has an unsupported type, garbage is written which cannot
  be read back by \code{load()}.

  Read one value from the open file and return it.  If no valid value
  is read, raise \code{EOFError}, \code{ValueError} or
  \code{TypeError}.  The file must be an open file object.

  Return the string that would be written to a file by
  \code{dump(value, file)}.  The value must be a supported type.

  Convert the string to a value.  If no valid value is found, raise
  \code{EOFError}, \code{ValueError} or \code{TypeError}.  Extra
  characters in the string are ignored.