# `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.

Advertencia

El módulo `marshal` no está destinado a ser seguro contra datos erróneos o construidos maliciosamente. Nunca deserializar con marshal los datos recibidos de una fuente no confiable o no autenticada.

Hay funciones que leen/escriben archivos, así como funciones que operan en objetos similares a bytes.

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`, `set`, `frozenset`, and (since `version` 5), `slice`. 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.

Distinto en la versión 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.

Distinto en la versión 3.14: Added format version 5, which allows marshalling slices.

El módulo define estas funciones:

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

  Escribe el valor en el archivo abierto. El valor debe ser un tipo admitido. El archivo debe ser un archivo binary file en el que se pueda escribir.

  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.

  El argumento version indica el formato de datos que `dump` debe usar (véase más adelante).

  Lanza un evento de auditoría `marshal.dumps` con argumentos `value`, `version`.

  Distinto en la versión 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.

  Lanza un evento de auditoría `marshal.load` sin argumentos.

  Nota

  Si un objeto que contiene un tipo no admitido se calcula con `dump()`, `load()` sustituirá `None` por el tipo «unmarshallable».

  Distinto en la versión 3.10: Esta llamada solía lanzar un evento de auditoría `code.__new__` para cada objeto código. Ahora lanza un único evento `marshal.load` para toda la operación de carga.

  Distinto en la versión 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.

  El argumento version indica el formato de datos que `dumps` debe usar (véase más adelante).

  Lanza un evento de auditoría `marshal.dumps` con argumentos `value`, `version`.

  Distinto en la versión 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.

  Lanza un evento de auditoría `marshal.loads` con argumento `bytes`.

  Distinto en la versión 3.10: Esta llamada solía lanzar un evento de auditoría `code.__new__` para cada objeto código. Ahora lanza un único evento `marshal.loads` para toda la operación de carga.

  Distinto en la versión 3.13: Added the allow_code parameter.

Además, se definen las siguientes constantes:

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

Notas al pie

[1]

El nombre de este módulo proviene de algunos términos utilizados por los diseñadores de Modula-3 (entre otros), que utilizan el término «marshalling» para el envío de datos de forma auto-contenida. Estrictamente hablando «marshalling», significa convertir algunos datos internos en un formato externo (por ejemplo, en un búfer RPC) y «unmarshalling» es el proceso inverso.