Data marshalling support — Python 3.14.3 documentation
Description: 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 functio...

# 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 several versions of the data format; see the `Python module documentation` for details.

Py_MARSHAL_VERSION

  The current format version. See `marshal.version`.

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.

  This function can fail, in which case it sets the error indicator. Use `PyErr_Occurred()` to check for that.

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

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

  This function can fail, in which case it sets the error indicator. Use `PyErr_Occurred()` to check for that.

PyObject *PyMarshal_WriteObjectToString(PyObject *value, int version)
  Return value: New reference.

  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 value: New reference.

  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 value: New reference.

  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 this 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 value: New reference.

  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`.