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 Sun, 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. 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.
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. The
singletons None, Ellipsis and 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 bytes-like objects.
The module defines these functions:
- marshal.dump(value, file[, version])¶
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
ValueErrorexception is raised — but garbage data will also be written to the file. The object will not be properly read back byload().The version argument indicates the data format that
dumpshould use (see below).Raises an auditing event
marshal.dumpswith argumentsvalue,version.
- marshal.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
EOFError,ValueErrororTypeError. The file must be a readable binary file.Raises an auditing event
marshal.loadwith no arguments.Note
If an object containing an unsupported type was marshalled with
dump(),load()will substituteNonefor 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 singlemarshal.loadevent for the entire load operation.
- marshal.dumps(value[, version])¶
Return the bytes object that would be written to a file by
dump(value, file). The value must be a supported type. Raise aValueErrorexception if value has (or contains an object that has) an unsupported type.The version argument indicates the data format that
dumpsshould use (see below).Raises an auditing event
marshal.dumpswith argumentsvalue,version.
- marshal.loads(bytes)¶
Convert the bytes-like object to a value. If no valid value is found, raise
EOFError,ValueErrororTypeError. Extra bytes in the input are ignored.Raises an auditing event
marshal.loadswith argumentbytes.Changed in version 3.10: This call used to raise a
code.__new__audit event for each code object. Now it raises a singlemarshal.loadsevent for the entire load operation.
In addition, the following constants are defined:
- marshal.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.
Footnotes