mirror of https://github.com/python/cpython
99 lines
3.7 KiB
ReStructuredText
99 lines
3.7 KiB
ReStructuredText
.. highlight:: c
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.. _marshalling-utils:
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Data marshalling support
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========================
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These routines allow C code to work with serialized objects using the same
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data format as the :mod:`marshal` module. There are functions to write data
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into the serialization format, and additional functions that can be used to
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read the data back. Files used to store marshalled data must be opened in
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binary mode.
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Numeric values are stored with the least significant byte first.
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The module supports two versions of the data format: version 0 is the
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historical version, version 1 shares interned strings in the file, and upon
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unmarshalling. Version 2 uses a binary format for floating-point numbers.
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``Py_MARSHAL_VERSION`` indicates the current file format (currently 2).
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.. c:function:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version)
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Marshal a :c:expr:`long` integer, *value*, to *file*. This will only write
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the least-significant 32 bits of *value*; regardless of the size of the
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native :c:expr:`long` type. *version* indicates the file format.
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This function can fail, in which case it sets the error indicator.
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Use :c:func:`PyErr_Occurred` to check for that.
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.. c:function:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)
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Marshal a Python object, *value*, to *file*.
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*version* indicates the file format.
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This function can fail, in which case it sets the error indicator.
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Use :c:func:`PyErr_Occurred` to check for that.
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.. c:function:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)
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Return a bytes object containing the marshalled representation of *value*.
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*version* indicates the file format.
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The following functions allow marshalled values to be read back in.
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.. c:function:: long PyMarshal_ReadLongFromFile(FILE *file)
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Return a C :c:expr:`long` from the data stream in a :c:expr:`FILE*` opened
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for reading. Only a 32-bit value can be read in using this function,
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regardless of the native size of :c:expr:`long`.
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On error, sets the appropriate exception (:exc:`EOFError`) and returns
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``-1``.
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.. c:function:: int PyMarshal_ReadShortFromFile(FILE *file)
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Return a C :c:expr:`short` from the data stream in a :c:expr:`FILE*` opened
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for reading. Only a 16-bit value can be read in using this function,
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regardless of the native size of :c:expr:`short`.
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On error, sets the appropriate exception (:exc:`EOFError`) and returns
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``-1``.
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.. c:function:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :c:expr:`FILE*` opened for
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reading.
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On error, sets the appropriate exception (:exc:`EOFError`, :exc:`ValueError`
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or :exc:`TypeError`) and returns ``NULL``.
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.. c:function:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :c:expr:`FILE*` opened for
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reading. Unlike :c:func:`PyMarshal_ReadObjectFromFile`, this function
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assumes that no further objects will be read from the file, allowing it to
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aggressively load file data into memory so that the de-serialization can
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operate from data in memory rather than reading a byte at a time from the
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file. Only use these variant if you are certain that you won't be reading
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anything else from the file.
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On error, sets the appropriate exception (:exc:`EOFError`, :exc:`ValueError`
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or :exc:`TypeError`) and returns ``NULL``.
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.. c:function:: PyObject* PyMarshal_ReadObjectFromString(const char *data, Py_ssize_t len)
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Return a Python object from the data stream in a byte buffer
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containing *len* bytes pointed to by *data*.
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On error, sets the appropriate exception (:exc:`EOFError`, :exc:`ValueError`
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or :exc:`TypeError`) and returns ``NULL``.
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