mirror of https://github.com/python/cpython
87 lines
3.5 KiB
ReStructuredText
87 lines
3.5 KiB
ReStructuredText
.. highlightlang:: 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 data
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format as the :mod:`marshal` module. There are functions to write data into the
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serialization format, and additional functions that can be used to read the data
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back. Files used to store marshalled data must be opened in 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 historical
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version, version 1 (new in Python 2.4) shares interned strings in the file, and
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upon unmarshalling. *Py_MARSHAL_VERSION* indicates the current file format
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(currently 1).
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.. cfunction:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version)
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Marshal a :ctype:`long` integer, *value*, to *file*. This will only write the
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least-significant 32 bits of *value*; regardless of the size of the native
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:ctype:`long` type. *version* indicates the file format.
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.. cfunction:: 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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.. cfunction:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)
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Return a string 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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XXX What about error detection? It appears that reading past the end of the
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file will always result in a negative numeric value (where that's relevant), but
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it's not clear that negative values won't be handled properly when there's no
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error. What's the right way to tell? Should only non-negative values be written
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using these routines?
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.. cfunction:: long PyMarshal_ReadLongFromFile(FILE *file)
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Return a C :ctype:`long` from the data stream in a :ctype:`FILE\*` opened for
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reading. Only a 32-bit value can be read in using this function, regardless of
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the native size of :ctype:`long`.
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.. cfunction:: int PyMarshal_ReadShortFromFile(FILE *file)
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Return a C :ctype:`short` from the data stream in a :ctype:`FILE\*` opened for
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reading. Only a 16-bit value can be read in using this function, regardless of
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the native size of :ctype:`short`.
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.. cfunction:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :ctype:`FILE\*` opened for
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reading. On error, sets the appropriate exception (:exc:`EOFError` or
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:exc:`TypeError`) and returns *NULL*.
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.. cfunction:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :ctype:`FILE\*` opened for
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reading. Unlike :cfunc:`PyMarshal_ReadObjectFromFile`, this function assumes
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that no further objects will be read from the file, allowing it to aggressively
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load file data into memory so that the de-serialization can operate from data in
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memory rather than reading a byte at a time from the file. Only use these
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variant if you are certain that you won't be reading anything else from the
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file. On error, sets the appropriate exception (:exc:`EOFError` or
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:exc:`TypeError`) and returns *NULL*.
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.. cfunction:: PyObject* PyMarshal_ReadObjectFromString(char *string, Py_ssize_t len)
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Return a Python object from the data stream in a character buffer containing
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*len* bytes pointed to by *string*. On error, sets the appropriate exception
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(:exc:`EOFError` or :exc:`TypeError`) and returns *NULL*.
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