60 lines
2.5 KiB
TeX
60 lines
2.5 KiB
TeX
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\section{Built-in Module \sectcode{marshal}}
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\bimodindex{marshal}
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This module contains functions that can read and write Python
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values in a binary format. The format is specific to Python, but
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independent of machine architecture issues (e.g., you can write a
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Python value to a file on a VAX, transport the file to a Mac, and read
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it back there). Details of the format not explained here; read the
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source if you're interested.%
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\footnote{The name of this module stems from a bit of terminology used
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by the designers of Modula-3 (amongst others), who use the term
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``marshalling'' for shipping of data around in a self-contained form.
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Strictly speaking, ``to marshal'' means to convert some data from
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internal to external form (in an RPC buffer for instance) and
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``unmarshalling'' for the reverse process.}
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Not all Python object types are supported; in general, only objects
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whose value is independent from a particular invocation of Python can
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be written and read by this module. The following types are supported:
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\code{None}, integers, long integers, floating point numbers,
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strings, tuples, lists, dictionaries, and code objects, where it
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should be understood that tuples, lists and dictionaries are only
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supported as long as the values contained therein are themselves
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supported; and recursive lists and dictionaries should not be written
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(they will cause an infinite loop).
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There are functions that read/write files as well as functions
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operating on strings.
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The module defines these functions:
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\renewcommand{\indexsubitem}{(in module marshal)}
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\begin{funcdesc}{dump}{value\, file}
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Write the value on the open file. The value must be a supported
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type. The file must be an open file object such as
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\code{sys.stdout} or returned by \code{open()} or
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\code{posix.popen()}.
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If the value has an unsupported type, garbage is written which cannot
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be read back by \code{load()}.
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\end{funcdesc}
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\begin{funcdesc}{load}{file}
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Read one value from the open file and return it. If no valid value
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is read, raise \code{EOFError}, \code{ValueError} or
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\code{TypeError}. The file must be an open file object.
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\end{funcdesc}
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\begin{funcdesc}{dumps}{value}
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Return the string that would be written to a file by
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\code{dump(value, file)}. The value must be a supported type.
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\end{funcdesc}
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\begin{funcdesc}{loads}{string}
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Convert the string to a value. If no valid value is found, raise
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\code{EOFError}, \code{ValueError} or \code{TypeError}. Extra
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characters in the string are ignored.
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\end{funcdesc}
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