1 .. highlightlang:: c

     2 

     3 .. _marshalling-utils:

     4 

     5 Data marshalling support

     6 ========================

     7 

     8 These routines allow C code to work with serialized objects using the same data

     9 format as the :mod:`marshal` module.  There are functions to write data into the

    10 serialization format, and additional functions that can be used to read the data

    11 back.  Files used to store marshalled data must be opened in binary mode.

    12 

    13 Numeric values are stored with the least significant byte first.

    14 

    15 The module supports two versions of the data format: version 0 is the historical

    16 version, version 1 (new in Python 2.4) shares interned strings in the file, and

    17 upon unmarshalling.  Version 2 (new in Python 2.5) uses a binary format for

    18 floating point numbers.

    19 *Py_MARSHAL_VERSION* indicates the current file format (currently 2).

    20 

    21 

    22 .. cfunction:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version)

    23 

    24    Marshal a :ctype:`long` integer, *value*, to *file*.  This will only write the

    25    least-significant 32 bits of *value*; regardless of the size of the native

    26    :ctype:`long` type.

    27 

    28    .. versionchanged:: 2.4

    29       *version* indicates the file format.

    30 

    31 

    32 .. cfunction:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)

    33 

    34    Marshal a Python object, *value*, to *file*.

    35 

    36    .. versionchanged:: 2.4

    37       *version* indicates the file format.

    38 

    39 

    40 .. cfunction:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)

    41 

    42    Return a string object containing the marshalled representation of *value*.

    43 

    44    .. versionchanged:: 2.4

    45       *version* indicates the file format.

    46 

    47 

    48 The following functions allow marshalled values to be read back in.

    49 

    50 XXX What about error detection?  It appears that reading past the end of the

    51 file will always result in a negative numeric value (where that's relevant), but

    52 it's not clear that negative values won't be handled properly when there's no

    53 error.  What's the right way to tell? Should only non-negative values be written

    54 using these routines?

    55 

    56 

    57 .. cfunction:: long PyMarshal_ReadLongFromFile(FILE *file)

    58 

    59    Return a C :ctype:`long` from the data stream in a :ctype:`FILE\*` opened for

    60    reading.  Only a 32-bit value can be read in using this function, regardless of

    61    the native size of :ctype:`long`.

    62 

    63 

    64 .. cfunction:: int PyMarshal_ReadShortFromFile(FILE *file)

    65 

    66    Return a C :ctype:`short` from the data stream in a :ctype:`FILE\*` opened for

    67    reading.  Only a 16-bit value can be read in using this function, regardless of

    68    the native size of :ctype:`short`.

    69 

    70 

    71 .. cfunction:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file)

    72 

    73    Return a Python object from the data stream in a :ctype:`FILE\*` opened for

    74    reading.  On error, sets the appropriate exception (:exc:`EOFError` or

    75    :exc:`TypeError`) and returns *NULL*.

    76 

    77 

    78 .. cfunction:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file)

    79 

    80    Return a Python object from the data stream in a :ctype:`FILE\*` opened for

    81    reading.  Unlike :cfunc:`PyMarshal_ReadObjectFromFile`, this function assumes

    82    that no further objects will be read from the file, allowing it to aggressively

    83    load file data into memory so that the de-serialization can operate from data in

    84    memory rather than reading a byte at a time from the file.  Only use these

    85    variant if you are certain that you won't be reading anything else from the

    86    file.  On error, sets the appropriate exception (:exc:`EOFError` or

    87    :exc:`TypeError`) and returns *NULL*.

    88 

    89 

    90 .. cfunction:: PyObject* PyMarshal_ReadObjectFromString(char *string, Py_ssize_t len)

    91 

    92    Return a Python object from the data stream in a character buffer containing

    93    *len* bytes pointed to by *string*.  On error, sets the appropriate exception

    94    (:exc:`EOFError` or :exc:`TypeError`) and returns *NULL*.