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/Doc/c-api/allocation.rst

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  1.. highlightlang:: c
  2
  3.. _allocating-objects:
  4
  5Allocating Objects on the Heap
  6==============================
  7
  8
  9.. cfunction:: PyObject* _PyObject_New(PyTypeObject *type)
 10
 11
 12.. cfunction:: PyVarObject* _PyObject_NewVar(PyTypeObject *type, Py_ssize_t size)
 13
 14   .. versionchanged:: 2.5
 15      This function used an :ctype:`int` type for *size*. This might require
 16      changes in your code for properly supporting 64-bit systems.
 17
 18
 19.. cfunction:: void _PyObject_Del(PyObject *op)
 20
 21
 22.. cfunction:: PyObject* PyObject_Init(PyObject *op, PyTypeObject *type)
 23
 24   Initialize a newly-allocated object *op* with its type and initial
 25   reference.  Returns the initialized object.  If *type* indicates that the
 26   object participates in the cyclic garbage detector, it is added to the
 27   detector's set of observed objects. Other fields of the object are not
 28   affected.
 29
 30
 31.. cfunction:: PyVarObject* PyObject_InitVar(PyVarObject *op, PyTypeObject *type, Py_ssize_t size)
 32
 33   This does everything :cfunc:`PyObject_Init` does, and also initializes the
 34   length information for a variable-size object.
 35
 36   .. versionchanged:: 2.5
 37      This function used an :ctype:`int` type for *size*. This might require
 38      changes in your code for properly supporting 64-bit systems.
 39
 40
 41.. cfunction:: TYPE* PyObject_New(TYPE, PyTypeObject *type)
 42
 43   Allocate a new Python object using the C structure type *TYPE* and the
 44   Python type object *type*.  Fields not defined by the Python object header
 45   are not initialized; the object's reference count will be one.  The size of
 46   the memory allocation is determined from the :attr:`tp_basicsize` field of
 47   the type object.
 48
 49
 50.. cfunction:: TYPE* PyObject_NewVar(TYPE, PyTypeObject *type, Py_ssize_t size)
 51
 52   Allocate a new Python object using the C structure type *TYPE* and the
 53   Python type object *type*.  Fields not defined by the Python object header
 54   are not initialized.  The allocated memory allows for the *TYPE* structure
 55   plus *size* fields of the size given by the :attr:`tp_itemsize` field of
 56   *type*.  This is useful for implementing objects like tuples, which are
 57   able to determine their size at construction time.  Embedding the array of
 58   fields into the same allocation decreases the number of allocations,
 59   improving the memory management efficiency.
 60
 61   .. versionchanged:: 2.5
 62      This function used an :ctype:`int` type for *size*. This might require
 63      changes in your code for properly supporting 64-bit systems.
 64
 65
 66.. cfunction:: void PyObject_Del(PyObject *op)
 67
 68   Releases memory allocated to an object using :cfunc:`PyObject_New` or
 69   :cfunc:`PyObject_NewVar`.  This is normally called from the
 70   :attr:`tp_dealloc` handler specified in the object's type.  The fields of
 71   the object should not be accessed after this call as the memory is no
 72   longer a valid Python object.
 73
 74
 75.. cfunction:: PyObject* Py_InitModule(char *name, PyMethodDef *methods)
 76
 77   Create a new module object based on a name and table of functions,
 78   returning the new module object.
 79
 80   .. versionchanged:: 2.3
 81      Older versions of Python did not support *NULL* as the value for the
 82      *methods* argument.
 83
 84
 85.. cfunction:: PyObject* Py_InitModule3(char *name, PyMethodDef *methods, char *doc)
 86
 87   Create a new module object based on a name and table of functions,
 88   returning the new module object.  If *doc* is non-*NULL*, it will be used
 89   to define the docstring for the module.
 90
 91   .. versionchanged:: 2.3
 92      Older versions of Python did not support *NULL* as the value for the
 93      *methods* argument.
 94
 95
 96.. cfunction:: PyObject* Py_InitModule4(char *name, PyMethodDef *methods, char *doc, PyObject *self, int apiver)
 97
 98   Create a new module object based on a name and table of functions,
 99   returning the new module object.  If *doc* is non-*NULL*, it will be used
100   to define the docstring for the module.  If *self* is non-*NULL*, it will
101   passed to the functions of the module as their (otherwise *NULL*) first
102   parameter.  (This was added as an experimental feature, and there are no
103   known uses in the current version of Python.)  For *apiver*, the only value
104   which should be passed is defined by the constant
105   :const:`PYTHON_API_VERSION`.
106
107   .. note::
108
109      Most uses of this function should probably be using the
110      :cfunc:`Py_InitModule3` instead; only use this if you are sure you need
111      it.
112
113   .. versionchanged:: 2.3
114      Older versions of Python did not support *NULL* as the value for the
115      *methods* argument.
116
117
118.. cvar:: PyObject _Py_NoneStruct
119
120   Object which is visible in Python as ``None``.  This should only be
121   accessed using the ``Py_None`` macro, which evaluates to a pointer to this
122   object.