Data marshalling support — Python documentation

Data marshalling support

These routines allow C code to work with serialized objects using the same data format as the 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).

void PyMarshal_WriteLongToFile(long value, FILE *file, int version)

Marshal a long integer, value, to file. This will only write the least-significant 32 bits of value; regardless of the size of the native long type. version indicates the file format.

void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)

Marshal a Python object, value, to file. version indicates the file format.

PyObject *PyMarshal_WriteObjectToString(PyObject *value, int version)

Return a bytes object containing the marshalled representation of value. version indicates the file format.

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

long PyMarshal_ReadLongFromFile(FILE *file)

Return a C long from the data stream in a FILE* opened for reading. Only a 32-bit value can be read in using this function, regardless of the native size of long.

On error, sets the appropriate exception (EOFError) and returns -1.

int PyMarshal_ReadShortFromFile(FILE *file)

Return a C short from the data stream in a FILE* opened for reading. Only a 16-bit value can be read in using this function, regardless of the native size of short.

On error, sets the appropriate exception (EOFError) and returns -1.

PyObject *PyMarshal_ReadObjectFromFile(FILE *file)

Return a Python object from the data stream in a FILE* opened for reading.

On error, sets the appropriate exception (EOFError, ValueError or TypeError) and returns NULL.

PyObject *PyMarshal_ReadLastObjectFromFile(FILE *file)

Return a Python object from the data stream in a FILE* opened for reading. Unlike 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 (EOFError, ValueError or TypeError) and returns NULL.

PyObject *PyMarshal_ReadObjectFromString(const char *data, Py_ssize_t len)

Return a Python object from the data stream in a byte buffer containing len bytes pointed to by data.

On error, sets the appropriate exception (EOFError, ValueError or TypeError) and returns NULL.