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3.8. Built-in Module 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.(1)
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:
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:
- dump (value, file) -- function of module marshal
-
Write the value on the open file. The value must be a supported
type. The file must be an open file object such as
sys.stdout or returned by open() or
posix.popen().
If the value has an unsupported type, garbage is written which cannot
be read back by load().
- load (file) -- function of module marshal
-
Read one value from the open file and return it. If no valid value
is read, raise
EOFError, ValueError or
TypeError. The file must be an open file object.
- dumps (value) -- function of module marshal
-
Return the string that would be written to a file by
dump(value, file). The value must be a supported type.
- loads (string) -- function of module marshal
-
Convert the string to a value. If no valid value is found, raise
EOFError, ValueError or TypeError. Extra
characters in the string are ignored.
---------- Footnotes ----------
(1)
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.