marshal —- Internal Python object serialization

This module contains functions that can read and write Python values in a binaryformat. The format is specific to Python, but independent of machinearchitecture 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 areundocumented on purpose; it may change between Python versions (although itrarely does). 1

This is not a general "persistence" module. For general persistence andtransfer of Python objects through RPC calls, see the modules pickle andshelve. The marshal module exists mainly to support reading andwriting the "pseudo-compiled" code for Python modules of .pyc files.Therefore, the Python maintainers reserve the right to modify the marshal formatin backward incompatible ways should the need arise. If you're serializing andde-serializing Python objects, use the pickle module instead — theperformance is comparable, version independence is guaranteed, and picklesupports a substantially wider range of objects than marshal.

警告

The marshal module is not intended to be secure against erroneous ormaliciously constructed data. Never unmarshal data received from anuntrusted or unauthenticated source.

Not all Python object types are supported; in general, only objects whose valueis independent from a particular invocation of Python can be written and read bythis module. The following types are supported: booleans, integers, floatingpoint numbers, complex numbers, strings, bytes, bytearrays, tuples, lists, sets,frozensets, dictionaries, and code objects, where it should be understood thattuples, lists, sets, frozensets and dictionaries are only supported as long asthe values contained therein are themselves supported. Thesingletons None, Ellipsis and StopIteration can also bemarshalled and unmarshalled.For format version lower than 3, recursive lists, sets and dictionaries cannotbe written (see below).

There are functions that read/write files as well as functions operating onbytes-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. Thefile must be a writeable binary file.

If the value has (or contains an object that has) an unsupported type, aValueError exception is raised —- but garbage data will also be writtento the file. The object will not be properly read back by load().

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

• 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 marshalformat), raise EOFError, ValueError or TypeError. Thefile must be a readable binary file.

注解

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

• marshal.dumps(value[, version])
• Return the bytes object that would be written to a file by dump(value, file). Thevalue must be a supported type. Raise a ValueError exception if valuehas (or contains an object that has) an unsupported type.

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

• marshal.loads(bytes)
• Convert the bytes-like object to a value. If no valid value is found, raiseEOFError, ValueError or TypeError. Extra bytes in theinput are ignored.

In addition, the following constants are defined:

• marshal.version
• Indicates the format that the module uses. Version 0 is the historicalformat, version 1 shares interned strings and version 2 uses a binary formatfor floating point numbers.Version 3 adds support for object instancing and recursion.The current version is 4.

脚注

• 1
• The name of this module stems from a bit of terminology used by the designers ofModula-3 (amongst others), who use the term "marshalling" for shipping of dataaround in a self-contained form. Strictly speaking, "to marshal" means toconvert some data from internal to external form (in an RPC buffer for instance)and "unmarshalling" for the reverse process.