mirror of https://github.com/python/cpython
87 lines
3.6 KiB
ReStructuredText
87 lines
3.6 KiB
ReStructuredText
.. highlightlang:: c
|
|
|
|
.. _marshalling-utils:
|
|
|
|
Data marshalling support
|
|
========================
|
|
|
|
These routines allow C code to work with serialized objects using the same data
|
|
format as the :mod:`marshal` module. There are functions to write data into the
|
|
serialization format, and additional functions that can be used to read the data
|
|
back. Files used to store marshalled data must be opened in binary mode.
|
|
|
|
Numeric values are stored with the least significant byte first.
|
|
|
|
The module supports two versions of the data format: version 0 is the historical
|
|
version, version 1 shares interned strings in the file, and upon unmarshalling.
|
|
Version 2 uses a binary format for floating point numbers.
|
|
*Py_MARSHAL_VERSION* indicates the current file format (currently 2).
|
|
|
|
|
|
.. cfunction:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version)
|
|
|
|
Marshal a :ctype:`long` integer, *value*, to *file*. This will only write the
|
|
least-significant 32 bits of *value*; regardless of the size of the native
|
|
:ctype:`long` type. *version* indicates the file format.
|
|
|
|
|
|
.. cfunction:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)
|
|
|
|
Marshal a Python object, *value*, to *file*.
|
|
*version* indicates the file format.
|
|
|
|
|
|
.. cfunction:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)
|
|
|
|
Return a string object containing the marshalled representation of *value*.
|
|
*version* indicates the file format.
|
|
|
|
|
|
The following functions allow marshalled values to be read back in.
|
|
|
|
XXX What about error detection? It appears that reading past the end of the
|
|
file will always result in a negative numeric value (where that's relevant), but
|
|
it's not clear that negative values won't be handled properly when there's no
|
|
error. What's the right way to tell? Should only non-negative values be written
|
|
using these routines?
|
|
|
|
|
|
.. cfunction:: long PyMarshal_ReadLongFromFile(FILE *file)
|
|
|
|
Return a C :ctype:`long` from the data stream in a :ctype:`FILE\*` opened for
|
|
reading. Only a 32-bit value can be read in using this function, regardless of
|
|
the native size of :ctype:`long`.
|
|
|
|
|
|
.. cfunction:: int PyMarshal_ReadShortFromFile(FILE *file)
|
|
|
|
Return a C :ctype:`short` from the data stream in a :ctype:`FILE\*` opened for
|
|
reading. Only a 16-bit value can be read in using this function, regardless of
|
|
the native size of :ctype:`short`.
|
|
|
|
|
|
.. cfunction:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file)
|
|
|
|
Return a Python object from the data stream in a :ctype:`FILE\*` opened for
|
|
reading. On error, sets the appropriate exception (:exc:`EOFError` or
|
|
:exc:`TypeError`) and returns *NULL*.
|
|
|
|
|
|
.. cfunction:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file)
|
|
|
|
Return a Python object from the data stream in a :ctype:`FILE\*` opened for
|
|
reading. Unlike :cfunc:`PyMarshal_ReadObjectFromFile`, this function assumes
|
|
that no further objects will be read from the file, allowing it to aggressively
|
|
load file data into memory so that the de-serialization can operate from data in
|
|
memory rather than reading a byte at a time from the file. Only use these
|
|
variant if you are certain that you won't be reading anything else from the
|
|
file. On error, sets the appropriate exception (:exc:`EOFError` or
|
|
:exc:`TypeError`) and returns *NULL*.
|
|
|
|
|
|
.. cfunction:: PyObject* PyMarshal_ReadObjectFromString(char *string, Py_ssize_t len)
|
|
|
|
Return a Python object from the data stream in a character buffer containing
|
|
*len* bytes pointed to by *string*. On error, sets the appropriate exception
|
|
(:exc:`EOFError` or :exc:`TypeError`) and returns *NULL*.
|