# cpython-withatomic / Doc / libmarshal.tex

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  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 \section{Built-in Module \sectcode{marshal}} \bimodindex{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 \code{posix.popen()}. If the value has an unsupported type, garbage is written which cannot be read back by \code{load()}. \end{funcdesc} \begin{funcdesc}{load}{file} 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. \end{funcdesc} \begin{funcdesc}{dumps}{value} Return the string that would be written to a file by \code{dump(value, file)}. The value must be a supported type. \end{funcdesc} \begin{funcdesc}{loads}{string} 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. \end{funcdesc} 
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