"marshal" — Internal Python object serialization
************************************************

======================================================================

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 Mac, and read it back there).
Details of the format are undocumented on purpose; it may change
between Python versions (although it rarely does). [1]

This is not a general “persistence” module.  For general persistence
and transfer of Python objects through RPC calls, see the modules
"pickle" and "shelve".  The "marshal" module exists mainly to support
reading and writing the “pseudo-compiled” code for Python modules of
".pyc" files. Therefore, the Python maintainers reserve the right to
modify the marshal format in backward incompatible ways should the
need arise. The format of code objects is not compatible between
Python versions, even if the version of the format is the same. De-
serializing a code object in the incorrect Python version has
undefined behavior. If you’re serializing and de-serializing Python
objects, use the "pickle" module instead – the performance is
comparable, version independence is guaranteed, and pickle supports a
substantially wider range of objects than marshal.

Warning:

  The "marshal" module is not intended to be secure against erroneous
  or maliciously constructed data.  Never unmarshal data received from
  an untrusted or unauthenticated source.

There are functions that read/write files as well as functions
operating on bytes-like objects.

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:

* Numeric types: "int", "bool", "float", "complex".

* Strings ("str") and "bytes". *Bytes-like objects* like "bytearray"
  are marshalled as "bytes".

* Containers: "tuple", "list", "dict", "frozendict" (since "version"
  6), "set", "frozenset", and "slice" (since "version" 5). It should
  be understood that these are supported only if the values contained
  therein are themselves supported. Recursive containers are supported
  since "version" 3.

* The singletons "None", "Ellipsis" and "StopIteration".

* "code" objects, if *allow_code* is true. See note above about
  version dependence.

Changed in version 3.4:

* Added format version 3, which supports marshalling recursive lists,
  sets and dictionaries.

* Added format version 4, which supports efficient representations of
  short strings.

Changed in version 3.14: Added format version 5, which allows
marshalling slices.

Changed in version 3.15: Added format version 6, which allows
marshalling "frozendict".

The module defines these functions:

marshal.dump(value, file, version=version, /, *, allow_code=True)

   Write the value on the open file.  The value must be a supported
   type.  The file must be a writeable *binary file*.

   If the value has (or contains an object that has) an unsupported
   type, a "ValueError" exception is raised — but garbage data will
   also be written to the file.  The object will not be properly read
   back by "load()". Code objects are only supported if *allow_code*
   is true.

   The *version* argument indicates the data format that "dump" should
   use (see below).

   Raises an auditing event "marshal.dumps" with arguments "value",
   "version".

   Changed in version 3.13: Added the *allow_code* parameter.

marshal.load(file, /, *, allow_code=True)

   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 "EOFError", "ValueError" or
   "TypeError". Code objects are only supported if *allow_code* is
   true. The file must be a readable *binary file*.

   Raises an auditing event "marshal.load" with no arguments.

   Note:

     If an object containing an unsupported type was marshalled with
     "dump()", "load()" will substitute "None" for the unmarshallable
     type.

   Changed in version 3.10: This call used to raise a "code.__new__"
   audit event for each code object. Now it raises a single
   "marshal.load" event for the entire load operation.

   Changed in version 3.13: Added the *allow_code* parameter.

marshal.dumps(value, version=version, /, *, allow_code=True)

   Return the bytes object that would be written to a file by
   "dump(value, file)".  The value must be a supported type.  Raise a
   "ValueError" exception if value has (or contains an object that
   has) an unsupported type. Code objects are only supported if
   *allow_code* is true.

   The *version* argument indicates the data format that "dumps"
   should use (see below).

   Raises an auditing event "marshal.dumps" with arguments "value",
   "version".

   Changed in version 3.13: Added the *allow_code* parameter.

marshal.loads(bytes, /, *, allow_code=True)

   Convert the *bytes-like object* to a value.  If no valid value is
   found, raise "EOFError", "ValueError" or "TypeError". Code objects
   are only supported if *allow_code* is true. Extra bytes in the
   input are ignored.

   Raises an auditing event "marshal.loads" with argument "bytes".

   Changed in version 3.10: This call used to raise a "code.__new__"
   audit event for each code object. Now it raises a single
   "marshal.loads" event for the entire load operation.

   Changed in version 3.13: Added the *allow_code* parameter.

In addition, the following constants are defined:

marshal.version

   Indicates the format that the module uses. Version 0 is the
   historical first version; subsequent versions add new features.
   Generally, a new version becomes the default when it is introduced.

   +---------+-----------------+------------------------------------------------------+
   | Version | Available since | New features                                         |
   |=========|=================|======================================================|
   | 1       | Python 2.4      | Sharing interned strings                             |
   +---------+-----------------+------------------------------------------------------+
   | 2       | Python 2.5      | Binary representation of floats                      |
   +---------+-----------------+------------------------------------------------------+
   | 3       | Python 3.4      | Support for object instancing and recursion          |
   +---------+-----------------+------------------------------------------------------+
   | 4       | Python 3.4      | Efficient representation of short strings            |
   +---------+-----------------+------------------------------------------------------+
   | 5       | Python 3.14     | Support for "slice" objects                          |
   +---------+-----------------+------------------------------------------------------+
   | 6       | Python 3.15     | Support for "frozendict" objects                     |
   +---------+-----------------+------------------------------------------------------+

-[ 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.
