\section{\module{marshal} ---         Internal Python object serialization} \declaremodule{builtin}{marshal}\modulesynopsis{Convert Python objects to streams of bytes and back                (with different constraints).}  This module contains functions that can read and write Pythonvalues in a binary format.  The format is specific to Python, butindependent of machine architecture issues (e.g., you can write aPython value to a file on a PC, transport the file to a Sun, and readit back there).  Details of the format are undocumented on purpose;it may change between Python versions (although it rarelydoes).\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.} This is not a general ``persistence'' module.  For general persistenceand transfer of Python objects through RPC calls, see the modules\refmodule{pickle} and \refmodule{shelve}.  The \module{marshal} module existsmainly to support reading and writing the ``pseudo-compiled'' code forPython modules of \file{.pyc} files.  Therefore, the Pythonmaintainers reserve the right to modify the marshal format in backwardincompatible ways should the need arise.  If you're serializing andde-serializing Python objects, use the \module{pickle} module instead.  \refstmodindex{pickle}\refstmodindex{shelve}\obindex{code} \begin{notice}[warning]The \module{marshal} module is not intended to be secure againsterroneous or maliciously constructed data.  Never unmarshal datareceived from an untrusted or unauthenticated source.\end{notice} Not all Python object types are supported; in general, only objectswhose value is independent from a particular invocation of Python canbe written and read by this module.  The following types are supported:\code{None}, integers, long integers, floating point numbers,strings, Unicode objects, tuples, lists, dictionaries, and codeobjects, where it should be understood that tuples, lists anddictionaries are only supported as long as the values containedtherein are themselves supported; and recursive lists and dictionariesshould not be written (they will cause infinite loops). \strong{Caveat:} On machines where C's \code{long int} type has more than32 bits (such as the DEC Alpha), it is possible to create plain Pythonintegers that are longer than 32 bits.If such an integer is marshaled and read back in on a machine whereC's \code{long int} type has only 32 bits, a Python long integer objectis returned instead.  While of a different type, the numeric value isthe same.  (This behavior is new in Python 2.2.  In earlier versions,all but the least-significant 32 bits of the value were lost, and awarning message was printed.) There are functions that read/write files as well as functionsoperating on strings. The module defines these functions: \begin{funcdesc}{dump}{value, file\optional{, version}}  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 \function{open()} or  \function{posix.popen()}.  It must be opened in binary mode  (\code{'wb'} or \code{'w+b'}).   If the value has (or contains an object that has) an unsupported type,  a \exception{ValueError} exception is raised --- but garbage data  will also be written to the file.  The object will not be properly  read back by \function{load()}.   \versionadded[The \var{version} argument indicates the data  format that \code{dump} should use (see below)]{2.4}\end{funcdesc} \begin{funcdesc}{load}{file}  Read one value from the open file and return it.  If no valid value  is read, raise \exception{EOFError}, \exception{ValueError} or  \exception{TypeError}.  The file must be an open file object opened  in binary mode (\code{'rb'} or \code{'r+b'}).   \warning{If an object containing an unsupported type was  marshalled with \function{dump()}, \function{load()} will substitute  \code{None} for the unmarshallable type.}\end{funcdesc} \begin{funcdesc}{dumps}{value\optional{, version}}  Return the string that would be written to a file by  \code{dump(\var{value}, \var{file})}.  The value must be a supported  type.  Raise a \exception{ValueError} exception if value has (or  contains an object that has) an unsupported type.   \versionadded[The \var{version} argument indicates the data  format that \code{dumps} should use (see below)]{2.4}\end{funcdesc} \begin{funcdesc}{loads}{string}  Convert the string to a value.  If no valid value is found, raise  \exception{EOFError}, \exception{ValueError} or  \exception{TypeError}.  Extra characters in the string are ignored.\end{funcdesc} In addition, the following constants are defined: \begin{datadesc}{version}  Indicates the format that the module uses. Version 0 is the  historical format, version 1 (added in Python 2.4) shares interned  strings and version 2 (added in Python 2.5) uses a binary format for  floating point numbers. The current version is 2.   \versionadded{2.4}\end{datadesc}