marshal — Internal Python object serialization

Serializing a data means converting it into a string of bytes and later reconstructing it from such a string. If the data is composed entirely of fundamental Python objects, the fastest way to serialize the data is by using marshal module (For user defined classes, Pickle should be preferred). Marshal module contains functions that can read and write Python values in a binary format.

The marshal module exists mainly to support reading and writing the “pseudo-compiled” code for Python modules of .pyc files. This module doesn’t support all Python object types.

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.



Functions :

  1. marshal.version :
    It indicates the format used by the module.

    • Version 0 – Historical format
    • Version 1 – Shares interned strings
    • Version 2 – Uses a binary format for floating point numbers
    • Version 3 – Support for object instancing and recursion
    • Version 4 – Current Version
  2. marshal.dumps(value[, version]) :
    The function returns the bytes object that would be written to a file by dump(value, file). The version argument indicates the data format that dumps should use. A ValueError exception is raised if the value has (or contains an object that has) an unsupported type.

    Example

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    # Python code to demonstrate serialization
    import marshal
      
    data = {12:'twelve', 'feep':list('ciao'), 1.23:4+5j
            (1,2,3):u'wer'}
    bytes = marshal.dumps(data)
      
    print bytes

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    Output

    {tfeep[tctitatog®Gáz®ó?y@@ittwelve(iiiuwer0}
    
  3. marshal.loads(bytes) :
    This function can reconstruct the data by converting the bytes-like object to a value. EOFError, ValueError or TypeError is raised if no value is found.

    Example

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    # Python code to demonstrate de-serialization
    import marshal
      
    data = {12:'twelve', 'feep':list('ciao'), 1.23:4+5j
            (1,2,3):u'wer'}
    bytes = marshal.dumps(data)
    redata = marshal.loads(bytes)
      
    print redata

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    Output

    {12: 'twelve', 1.23: (4+5j), 'feep': ['c', 'i', 'a', 'o'], (1, 2, 3): u'wer'}
    
  4. marshal.dump(value, file[, version]) :
    This function is used to write the supported type value on the open writeable binary file. A ValueError exception is raised if the value has an unsupported type.
  5. marshal.load(file) :
    This function reads one value from the open readable binary file and returns it. EOFError, ValueError or TypeError is raised if no value is read.

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