cpython/Doc/c-api/long.rst

.. highlight:: c

.. _longobjects:

Integer Objects
---------------

.. index:: pair: object; long integer
           pair: object; integer

All integers are implemented as "long" integer objects of arbitrary size.

On error, most ``PyLong_As*`` APIs return ``(return type)-1`` which cannot be
distinguished from a number.  Use :c:func:`PyErr_Occurred` to disambiguate.

.. c:type:: PyLongObject

   This subtype of :c:type:`PyObject` represents a Python integer object.


.. c:var:: PyTypeObject PyLong_Type

   This instance of :c:type:`PyTypeObject` represents the Python integer type.
   This is the same object as :class:`int` in the Python layer.


.. c:function:: int PyLong_Check(PyObject *p)

   Return true if its argument is a :c:type:`PyLongObject` or a subtype of
   :c:type:`PyLongObject`.  This function always succeeds.


.. c:function:: int PyLong_CheckExact(PyObject *p)

   Return true if its argument is a :c:type:`PyLongObject`, but not a subtype of
   :c:type:`PyLongObject`.  This function always succeeds.


.. c:function:: PyObject* PyLong_FromLong(long v)

   Return a new :c:type:`PyLongObject` object from *v*, or ``NULL`` on failure.

   The current implementation keeps an array of integer objects for all integers
   between ``-5`` and ``256``. When you create an int in that range you actually
   just get back a reference to the existing object.


.. c:function:: PyObject* PyLong_FromUnsignedLong(unsigned long v)

   Return a new :c:type:`PyLongObject` object from a C :c:expr:`unsigned long`, or
   ``NULL`` on failure.


.. c:function:: PyObject* PyLong_FromSsize_t(Py_ssize_t v)

   Return a new :c:type:`PyLongObject` object from a C :c:type:`Py_ssize_t`, or
   ``NULL`` on failure.


.. c:function:: PyObject* PyLong_FromSize_t(size_t v)

   Return a new :c:type:`PyLongObject` object from a C :c:type:`size_t`, or
   ``NULL`` on failure.


.. c:function:: PyObject* PyLong_FromLongLong(long long v)

   Return a new :c:type:`PyLongObject` object from a C :c:expr:`long long`, or ``NULL``
   on failure.


.. c:function:: PyObject* PyLong_FromUnsignedLongLong(unsigned long long v)

   Return a new :c:type:`PyLongObject` object from a C :c:expr:`unsigned long long`,
   or ``NULL`` on failure.


.. c:function:: PyObject* PyLong_FromDouble(double v)

   Return a new :c:type:`PyLongObject` object from the integer part of *v*, or
   ``NULL`` on failure.


.. c:function:: PyObject* PyLong_FromString(const char *str, char **pend, int base)

   Return a new :c:type:`PyLongObject` based on the string value in *str*, which
   is interpreted according to the radix in *base*, or ``NULL`` on failure.  If
   *pend* is non-``NULL``, *\*pend* will point to the end of *str* on success or
   to the first character that could not be processed on error.  If *base* is ``0``,
   *str* is interpreted using the :ref:`integers` definition; in this case, leading
   zeros in a non-zero decimal number raises a :exc:`ValueError`.  If *base* is not
   ``0``, it must be between ``2`` and ``36``, inclusive.  Leading and trailing
   whitespace and single underscores after a base specifier and between digits are
   ignored.  If there are no digits or *str* is not NULL-terminated following the
   digits and trailing whitespace, :exc:`ValueError` will be raised.

   .. seealso:: Python methods :meth:`int.to_bytes` and :meth:`int.from_bytes`
      to convert a :c:type:`PyLongObject` to/from an array of bytes in base
      ``256``. You can call those from C using :c:func:`PyObject_CallMethod`.


.. c:function:: PyObject* PyLong_FromUnicodeObject(PyObject *u, int base)

   Convert a sequence of Unicode digits in the string *u* to a Python integer
   value.

   .. versionadded:: 3.3


.. c:function:: PyObject* PyLong_FromVoidPtr(void *p)

   Create a Python integer from the pointer *p*. The pointer value can be
   retrieved from the resulting value using :c:func:`PyLong_AsVoidPtr`.


.. c:function:: PyObject* PyLong_FromNativeBytes(const void* buffer, size_t n_bytes, int flags)

   Create a Python integer from the value contained in the first *n_bytes* of
   *buffer*, interpreted as a two's-complement signed number.

   *flags* are as for :c:func:`PyLong_AsNativeBytes`. Passing ``-1`` will select
   the native endian that CPython was compiled with and assume that the
   most-significant bit is a sign bit. Passing
   ``Py_ASNATIVEBYTES_UNSIGNED_BUFFER`` will produce the same result as calling
   :c:func:`PyLong_FromUnsignedNativeBytes`. Other flags are ignored.

   .. versionadded:: 3.13


.. c:function:: PyObject* PyLong_FromUnsignedNativeBytes(const void* buffer, size_t n_bytes, int flags)

   Create a Python integer from the value contained in the first *n_bytes* of
   *buffer*, interpreted as an unsigned number.

   *flags* are as for :c:func:`PyLong_AsNativeBytes`. Passing ``-1`` will select
   the native endian that CPython was compiled with and assume that the
   most-significant bit is not a sign bit. Flags other than endian are ignored.

   .. versionadded:: 3.13


.. XXX alias PyLong_AS_LONG (for now)
.. c:function:: long PyLong_AsLong(PyObject *obj)

   .. index::
      single: LONG_MAX (C macro)
      single: OverflowError (built-in exception)

   Return a C :c:expr:`long` representation of *obj*.  If *obj* is not an
   instance of :c:type:`PyLongObject`, first call its :meth:`~object.__index__` method
   (if present) to convert it to a :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *obj* is out of range for a
   :c:expr:`long`.

   Returns ``-1`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: int PyLong_AsInt(PyObject *obj)

   Similar to :c:func:`PyLong_AsLong`, but store the result in a C
   :c:expr:`int` instead of a C :c:expr:`long`.

   .. versionadded:: 3.13


.. c:function:: long PyLong_AsLongAndOverflow(PyObject *obj, int *overflow)

   Return a C :c:expr:`long` representation of *obj*.  If *obj* is not an
   instance of :c:type:`PyLongObject`, first call its :meth:`~object.__index__`
   method (if present) to convert it to a :c:type:`PyLongObject`.

   If the value of *obj* is greater than :c:macro:`LONG_MAX` or less than
   :c:macro:`LONG_MIN`, set *\*overflow* to ``1`` or ``-1``, respectively, and
   return ``-1``; otherwise, set *\*overflow* to ``0``.  If any other exception
   occurs set *\*overflow* to ``0`` and return ``-1`` as usual.

   Returns ``-1`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: long long PyLong_AsLongLong(PyObject *obj)

   .. index::
      single: OverflowError (built-in exception)

   Return a C :c:expr:`long long` representation of *obj*.  If *obj* is not an
   instance of :c:type:`PyLongObject`, first call its :meth:`~object.__index__` method
   (if present) to convert it to a :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *obj* is out of range for a
   :c:expr:`long long`.

   Returns ``-1`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: long long PyLong_AsLongLongAndOverflow(PyObject *obj, int *overflow)

   Return a C :c:expr:`long long` representation of *obj*.  If *obj* is not an
   instance of :c:type:`PyLongObject`, first call its :meth:`~object.__index__` method
   (if present) to convert it to a :c:type:`PyLongObject`.

   If the value of *obj* is greater than :c:macro:`LLONG_MAX` or less than
   :c:macro:`LLONG_MIN`, set *\*overflow* to ``1`` or ``-1``, respectively,
   and return ``-1``; otherwise, set *\*overflow* to ``0``.  If any other
   exception occurs set *\*overflow* to ``0`` and return ``-1`` as usual.

   Returns ``-1`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.

   .. versionadded:: 3.2

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: Py_ssize_t PyLong_AsSsize_t(PyObject *pylong)

   .. index::
      single: PY_SSIZE_T_MAX (C macro)
      single: OverflowError (built-in exception)

   Return a C :c:type:`Py_ssize_t` representation of *pylong*.  *pylong* must
   be an instance of :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *pylong* is out of range for a
   :c:type:`Py_ssize_t`.

   Returns ``-1`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.


.. c:function:: unsigned long PyLong_AsUnsignedLong(PyObject *pylong)

   .. index::
      single: ULONG_MAX (C macro)
      single: OverflowError (built-in exception)

   Return a C :c:expr:`unsigned long` representation of *pylong*.  *pylong*
   must be an instance of :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *pylong* is out of range for a
   :c:expr:`unsigned long`.

   Returns ``(unsigned long)-1`` on error.
   Use :c:func:`PyErr_Occurred` to disambiguate.


.. c:function:: size_t PyLong_AsSize_t(PyObject *pylong)

   .. index::
      single: SIZE_MAX (C macro)
      single: OverflowError (built-in exception)

   Return a C :c:type:`size_t` representation of *pylong*.  *pylong* must be
   an instance of :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *pylong* is out of range for a
   :c:type:`size_t`.

   Returns ``(size_t)-1`` on error.
   Use :c:func:`PyErr_Occurred` to disambiguate.


.. c:function:: unsigned long long PyLong_AsUnsignedLongLong(PyObject *pylong)

   .. index::
      single: OverflowError (built-in exception)

   Return a C :c:expr:`unsigned long long` representation of *pylong*.  *pylong*
   must be an instance of :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *pylong* is out of range for an
   :c:expr:`unsigned long long`.

   Returns ``(unsigned long long)-1`` on error.
   Use :c:func:`PyErr_Occurred` to disambiguate.

   .. versionchanged:: 3.1
      A negative *pylong* now raises :exc:`OverflowError`, not :exc:`TypeError`.


.. c:function:: unsigned long PyLong_AsUnsignedLongMask(PyObject *obj)

   Return a C :c:expr:`unsigned long` representation of *obj*.  If *obj* is not
   an instance of :c:type:`PyLongObject`, first call its :meth:`~object.__index__`
   method (if present) to convert it to a :c:type:`PyLongObject`.

   If the value of *obj* is out of range for an :c:expr:`unsigned long`,
   return the reduction of that value modulo ``ULONG_MAX + 1``.

   Returns ``(unsigned long)-1`` on error.  Use :c:func:`PyErr_Occurred` to
   disambiguate.

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: unsigned long long PyLong_AsUnsignedLongLongMask(PyObject *obj)

   Return a C :c:expr:`unsigned long long` representation of *obj*.  If *obj*
   is not an instance of :c:type:`PyLongObject`, first call its
   :meth:`~object.__index__` method (if present) to convert it to a
   :c:type:`PyLongObject`.

   If the value of *obj* is out of range for an :c:expr:`unsigned long long`,
   return the reduction of that value modulo ``ULLONG_MAX + 1``.

   Returns ``(unsigned long long)-1`` on error.  Use :c:func:`PyErr_Occurred`
   to disambiguate.

   .. versionchanged:: 3.8
      Use :meth:`~object.__index__` if available.

   .. versionchanged:: 3.10
      This function will no longer use :meth:`~object.__int__`.


.. c:function:: double PyLong_AsDouble(PyObject *pylong)

   Return a C :c:expr:`double` representation of *pylong*.  *pylong* must be
   an instance of :c:type:`PyLongObject`.

   Raise :exc:`OverflowError` if the value of *pylong* is out of range for a
   :c:expr:`double`.

   Returns ``-1.0`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.


.. c:function:: void* PyLong_AsVoidPtr(PyObject *pylong)

   Convert a Python integer *pylong* to a C :c:expr:`void` pointer.
   If *pylong* cannot be converted, an :exc:`OverflowError` will be raised.  This
   is only assured to produce a usable :c:expr:`void` pointer for values created
   with :c:func:`PyLong_FromVoidPtr`.

   Returns ``NULL`` on error.  Use :c:func:`PyErr_Occurred` to disambiguate.


.. c:function:: Py_ssize_t PyLong_AsNativeBytes(PyObject *pylong, void* buffer, Py_ssize_t n_bytes, int flags)

   Copy the Python integer value *pylong* to a native *buffer* of size
   *n_bytes*. The *flags* can be set to ``-1`` to behave similarly to a C cast,
   or to values documented below to control the behavior.

   Returns ``-1`` with an exception raised on error.  This may happen if
   *pylong* cannot be interpreted as an integer, or if *pylong* was negative
   and the ``Py_ASNATIVEBYTES_REJECT_NEGATIVE`` flag was set.

   Otherwise, returns the number of bytes required to store the value.
   If this is equal to or less than *n_bytes*, the entire value was copied.
   All *n_bytes* of the buffer are written: large buffers are padded with
   zeroes.

   If the returned value is greater than than *n_bytes*, the value was
   truncated: as many of the lowest bits of the value as could fit are written,
   and the higher bits are ignored. This matches the typical behavior
   of a C-style downcast.

   .. note::

      Overflow is not considered an error. If the returned value
      is larger than *n_bytes*, most significant bits were discarded.

   ``0`` will never be returned.

   Values are always copied as two's-complement.

   Usage example::

      int32_t value;
      Py_ssize_t bytes = PyLong_AsNativeBytes(pylong, &value, sizeof(value), -1);
      if (bytes < 0) {
          // Failed. A Python exception was set with the reason.
          return NULL;
      }
      else if (bytes <= (Py_ssize_t)sizeof(value)) {
          // Success!
      }
      else {
          // Overflow occurred, but 'value' contains the truncated
          // lowest bits of pylong.
      }

   Passing zero to *n_bytes* will return the size of a buffer that would
   be large enough to hold the value. This may be larger than technically
   necessary, but not unreasonably so.

   .. note::

      Passing *n_bytes=0* to this function is not an accurate way to determine
      the bit length of a value.

   If *n_bytes=0*, *buffer* may be ``NULL``.

   To get at the entire Python value of an unknown size, the function can be
   called twice: first to determine the buffer size, then to fill it::

      // Ask how much space we need.
      Py_ssize_t expected = PyLong_AsNativeBytes(pylong, NULL, 0, -1);
      if (expected < 0) {
          // Failed. A Python exception was set with the reason.
          return NULL;
      }
      assert(expected != 0);  // Impossible per the API definition.
      uint8_t *bignum = malloc(expected);
      if (!bignum) {
          PyErr_SetString(PyExc_MemoryError, "bignum malloc failed.");
          return NULL;
      }
      // Safely get the entire value.
      Py_ssize_t bytes = PyLong_AsNativeBytes(pylong, bignum, expected, -1);
      if (bytes < 0) {  // Exception has been set.
          free(bignum);
          return NULL;
      }
      else if (bytes > expected) {  // This should not be possible.
          PyErr_SetString(PyExc_RuntimeError,
              "Unexpected bignum truncation after a size check.");
          free(bignum);
          return NULL;
      }
      // The expected success given the above pre-check.
      // ... use bignum ...
      free(bignum);

   *flags* is either ``-1`` (``Py_ASNATIVEBYTES_DEFAULTS``) to select defaults
   that behave most like a C cast, or a combintation of the other flags in
   the table below.
   Note that ``-1`` cannot be combined with other flags.

   Currently, ``-1`` corresponds to
   ``Py_ASNATIVEBYTES_NATIVE_ENDIAN | Py_ASNATIVEBYTES_UNSIGNED_BUFFER``.

   ============================================= ======
   Flag                                          Value
   ============================================= ======
   .. c:macro:: Py_ASNATIVEBYTES_DEFAULTS        ``-1``
   .. c:macro:: Py_ASNATIVEBYTES_BIG_ENDIAN      ``0``
   .. c:macro:: Py_ASNATIVEBYTES_LITTLE_ENDIAN   ``1``
   .. c:macro:: Py_ASNATIVEBYTES_NATIVE_ENDIAN   ``3``
   .. c:macro:: Py_ASNATIVEBYTES_UNSIGNED_BUFFER ``4``
   .. c:macro:: Py_ASNATIVEBYTES_REJECT_NEGATIVE ``8``
   ============================================= ======

   Specifying ``Py_ASNATIVEBYTES_NATIVE_ENDIAN`` will override any other endian
   flags. Passing ``2`` is reserved.

   By default, sufficient buffer will be requested to include a sign bit.
   For example, when converting 128 with *n_bytes=1*, the function will return
   2 (or more) in order to store a zero sign bit.

   If ``Py_ASNATIVEBYTES_UNSIGNED_BUFFER`` is specified, a zero sign bit
   will be omitted from size calculations. This allows, for example, 128 to fit
   in a single-byte buffer. If the destination buffer is later treated as
   signed, a positive input value may become negative.
   Note that the flag does not affect handling of negative values: for those,
   space for a sign bit is always requested.

   Specifying ``Py_ASNATIVEBYTES_REJECT_NEGATIVE`` causes an exception to be set
   if *pylong* is negative. Without this flag, negative values will be copied
   provided there is enough space for at least one sign bit, regardless of
   whether ``Py_ASNATIVEBYTES_UNSIGNED_BUFFER`` was specified.

   .. note::

      With the default *flags* (``-1``, or *UNSIGNED_BUFFER*  without
      *REJECT_NEGATIVE*), multiple Python integers can map to a single value
      without overflow. For example, both ``255`` and ``-1`` fit a single-byte
      buffer and set all its bits.
      This matches typical C cast behavior.

   .. versionadded:: 3.13


.. c:function:: int PyUnstable_Long_IsCompact(const PyLongObject* op)

   Return 1 if *op* is compact, 0 otherwise.

   This function makes it possible for performance-critical code to implement
   a “fast path” for small integers. For compact values use
   :c:func:`PyUnstable_Long_CompactValue`; for others fall back to a
   :c:func:`PyLong_As* <PyLong_AsSize_t>` function or
   :c:func:`PyLong_AsNativeBytes`.

   The speedup is expected to be negligible for most users.

   Exactly what values are considered compact is an implementation detail
   and is subject to change.

.. c:function:: Py_ssize_t PyUnstable_Long_CompactValue(const PyLongObject* op)

   If *op* is compact, as determined by :c:func:`PyUnstable_Long_IsCompact`,
   return its value.

   Otherwise, the return value is undefined.