mirror of https://github.com/python/cpython
120 lines
4.8 KiB
ReStructuredText
120 lines
4.8 KiB
ReStructuredText
:mod:`marshal` --- Internal Python object serialization
|
|
=======================================================
|
|
|
|
.. module:: marshal
|
|
:synopsis: Convert Python objects to streams of bytes and back (with different
|
|
constraints).
|
|
|
|
|
|
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 PC,
|
|
transport the file to a Sun, and read it back there). Details of the format are
|
|
undocumented on purpose; it may change between Python versions (although it
|
|
rarely does). [#]_
|
|
|
|
.. index::
|
|
module: pickle
|
|
module: shelve
|
|
object: code
|
|
|
|
This is not a general "persistence" module. For general persistence and
|
|
transfer of Python objects through RPC calls, see the modules :mod:`pickle` and
|
|
:mod:`shelve`. The :mod:`marshal` module exists mainly to support reading and
|
|
writing the "pseudo-compiled" code for Python modules of :file:`.pyc` files.
|
|
Therefore, the Python maintainers reserve the right to modify the marshal format
|
|
in backward incompatible ways should the need arise. If you're serializing and
|
|
de-serializing Python objects, use the :mod:`pickle` module instead -- the
|
|
performance is comparable, version independence is guaranteed, and pickle
|
|
supports a substantially wider range of objects than marshal.
|
|
|
|
.. warning::
|
|
|
|
The :mod:`marshal` module is not intended to be secure against erroneous or
|
|
maliciously constructed data. Never unmarshal data received from an
|
|
untrusted or unauthenticated source.
|
|
|
|
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: booleans, integers, floating
|
|
point numbers, complex numbers, strings, bytes, bytearrays, tuples, lists, sets,
|
|
frozensets, dictionaries, and code objects, where it should be understood that
|
|
tuples, lists, sets, frozensets and dictionaries are only supported as long as
|
|
the values contained therein are themselves supported.
|
|
singletons :const:`None`, :const:`Ellipsis` and :exc:`StopIteration` can also be
|
|
marshalled and unmarshalled.
|
|
For format *version* lower than 3, recursive lists, sets and dictionaries cannot
|
|
be written (see below).
|
|
|
|
There are functions that read/write files as well as functions operating on
|
|
strings.
|
|
|
|
The module defines these functions:
|
|
|
|
|
|
.. function:: dump(value, file[, 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 ``sys.stdout`` or returned by
|
|
:func:`open` or :func:`os.popen`. It must be opened in binary mode (``'wb'``
|
|
or ``'w+b'``).
|
|
|
|
If the value has (or contains an object that has) an unsupported type, a
|
|
:exc:`ValueError` exception is raised --- but garbage data will also be written
|
|
to the file. The object will not be properly read back by :func:`load`.
|
|
|
|
The *version* argument indicates the data format that ``dump`` should use
|
|
(see below).
|
|
|
|
|
|
.. function:: load(file)
|
|
|
|
Read one value from the open file and return it. If no valid value is read
|
|
(e.g. because the data has a different Python version's incompatible marshal
|
|
format), raise :exc:`EOFError`, :exc:`ValueError` or :exc:`TypeError`. The
|
|
file must be an open file object opened in binary mode (``'rb'`` or
|
|
``'r+b'``).
|
|
|
|
.. note::
|
|
|
|
If an object containing an unsupported type was marshalled with :func:`dump`,
|
|
:func:`load` will substitute ``None`` for the unmarshallable type.
|
|
|
|
|
|
.. function:: dumps(value[, version])
|
|
|
|
Return the string that would be written to a file by ``dump(value, file)``. The
|
|
value must be a supported type. Raise a :exc:`ValueError` exception if value
|
|
has (or contains an object that has) an unsupported type.
|
|
|
|
The *version* argument indicates the data format that ``dumps`` should use
|
|
(see below).
|
|
|
|
|
|
.. function:: loads(string)
|
|
|
|
Convert the string to a value. If no valid value is found, raise
|
|
:exc:`EOFError`, :exc:`ValueError` or :exc:`TypeError`. Extra characters in the
|
|
string are ignored.
|
|
|
|
|
|
In addition, the following constants are defined:
|
|
|
|
.. data:: version
|
|
|
|
Indicates the format that the module uses. Version 0 is the historical
|
|
format, version 1 shares interned strings and version 2 uses a binary format
|
|
for floating point numbers.
|
|
Version 3 adds support for object instancing and recursion.
|
|
The current version is 4.
|
|
|
|
|
|
.. rubric:: Footnotes
|
|
|
|
.. [#] 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.
|
|
|