# 浮點數（Floating-Point）物件

type PyFloatObject

  This subtype of `PyObject` represents a Python floating-point object.

PyTypeObject PyFloat_Type
  為 穩定 ABI 的一部分.

  This instance of `PyTypeObject` represents the Python floating-point type. This is the same object as `float` in the Python layer.

int PyFloat_Check( PyObject *p)

  Return true if its argument is a `PyFloatObject` or a subtype of `PyFloatObject`. This function always succeeds.

int PyFloat_CheckExact( PyObject *p)

  Return true if its argument is a `PyFloatObject`, but not a subtype of `PyFloatObject`. This function always succeeds.

PyObject *PyFloat_FromString( PyObject *str)
  回傳值：新的參照。 為 穩定 ABI 的一部分.

  Create a `PyFloatObject` object based on the string value in str, or `NULL` on failure.

PyObject *PyFloat_FromDouble(double v)
  回傳值：新的參照。 為 穩定 ABI 的一部分.

  Create a `PyFloatObject` object from v, or `NULL` on failure.

double PyFloat_AsDouble( PyObject *pyfloat)
  為 穩定 ABI 的一部分.

  Return a C double representation of the contents of pyfloat. If pyfloat is not a Python floating-point object but has a `__float__()` method, this method will first be called to convert pyfloat into a float. If `__float__()` is not defined then it falls back to `__index__()`. This method returns `-1.0` upon failure, so one should call `PyErr_Occurred()` to check for errors.

  在 3.8 版的變更: Use `__index__()` if available.

double PyFloat_AS_DOUBLE( PyObject *pyfloat)

  Return a C double representation of the contents of pyfloat, but without error checking.

PyObject *PyFloat_GetInfo(void)
  回傳值：新的參照。 為 穩定 ABI 的一部分.

  Return a structseq instance which contains information about the precision, minimum and maximum values of a float. It's a thin wrapper around the header file `float.h`.

double PyFloat_GetMax()
  為 穩定 ABI 的一部分.

  Return the maximum representable finite float DBL_MAX as C double.

double PyFloat_GetMin()
  為 穩定 ABI 的一部分.

  Return the minimum normalized positive float DBL_MIN as C double.

## Pack and Unpack functions

The pack and unpack functions provide an efficient platform-independent way to store floating-point values as byte strings. The Pack routines produce a bytes string from a C double, and the Unpack routines produce a C double from such a bytes string. The suffix (2, 4 or 8) specifies the number of bytes in the bytes string.

On platforms that appear to use IEEE 754 formats these functions work by copying bits. On other platforms, the 2-byte format is identical to the IEEE 754 binary16 half-precision format, the 4-byte format (32-bit) is identical to the IEEE 754 binary32 single precision format, and the 8-byte format to the IEEE 754 binary64 double precision format, although the packing of INFs and NaNs (if such things exist on the platform) isn't handled correctly, and attempting to unpack a bytes string containing an IEEE INF or NaN will raise an exception.

Note that NaNs type may not be preserved on IEEE platforms (silent NaN become quiet), for example on x86 systems in 32-bit mode.

On non-IEEE platforms with more precision, or larger dynamic range, than IEEE 754 supports, not all values can be packed; on non-IEEE platforms with less precision, or smaller dynamic range, not all values can be unpacked. What happens in such cases is partly accidental (alas).

在 3.11 版被加入.

### Pack functions

The pack routines write 2, 4 or 8 bytes, starting at p. le is an int argument, non-zero if you want the bytes string in little-endian format (exponent last, at `p+1`, `p+3`, or `p+6` `p+7`), zero if you want big-endian format (exponent first, at p). The `PY_BIG_ENDIAN` constant can be used to use the native endian: it is equal to `1` on big endian processor, or `0` on little endian processor.

Return value: `0` if all is OK, `-1` if error (and an exception is set, most likely `OverflowError`).

There are two problems on non-IEEE platforms:

- What this does is undefined if x is a NaN or infinity.

- `-0.0` 和 `+0.0` 會產生同樣的位元組字串。

int PyFloat_Pack2(double x, char *p, int le)

  Pack a C double as the IEEE 754 binary16 half-precision format.

int PyFloat_Pack4(double x, char *p, int le)

  Pack a C double as the IEEE 754 binary32 single precision format.

int PyFloat_Pack8(double x, char *p, int le)

  Pack a C double as the IEEE 754 binary64 double precision format.

### Unpack functions

The unpack routines read 2, 4 or 8 bytes, starting at p. le is an int argument, non-zero if the bytes string is in little-endian format (exponent last, at `p+1`, `p+3` or `p+6` and `p+7`), zero if big-endian (exponent first, at p). The `PY_BIG_ENDIAN` constant can be used to use the native endian: it is equal to `1` on big endian processor, or `0` on little endian processor.

Return value: The unpacked double. On error, this is `-1.0` and `PyErr_Occurred()` is true (and an exception is set, most likely `OverflowError`).

Note that on a non-IEEE platform this will refuse to unpack a bytes string that represents a NaN or infinity.

double PyFloat_Unpack2(const char *p, int le)

  Unpack the IEEE 754 binary16 half-precision format as a C double.

double PyFloat_Unpack4(const char *p, int le)

  Unpack the IEEE 754 binary32 single precision format as a C double.

double PyFloat_Unpack8(const char *p, int le)

  Unpack the IEEE 754 binary64 double precision format as a C double.