浮點(diǎn)數(shù)對(duì)象?

type PyFloatObject?

這個(gè)C類型 PyObject 的子類型代表一個(gè)Python浮點(diǎn)數(shù)對(duì)象。

PyTypeObject PyFloat_Type?
Part of the Stable ABI.

這是個(gè)屬于C類型 PyTypeObject 的代表Python浮點(diǎn)類型的實(shí)例。在Python層面的類型 float 是同一個(gè)對(duì)象。

int PyFloat_Check(PyObject *p)?

如果它的參數(shù)是一個(gè) PyFloatObject 或者 PyFloatObject 的子類型則返回真值。 此函數(shù)總是會(huì)成功執(zhí)行。

int PyFloat_CheckExact(PyObject *p)?

如果它的參數(shù)是一個(gè) PyFloatObject 但不是 PyFloatObject 的子類型則返回真值。 此函數(shù)總是會(huì)成功執(zhí)行。

PyObject *PyFloat_FromString(PyObject *str)?
Return value: New reference. Part of the Stable ABI.

根據(jù)字符串 str 的值創(chuàng)建一個(gè) PyFloatObject，失敗時(shí)返回 NULL。

PyObject *PyFloat_FromDouble(double v)?
Return value: New reference. Part of the Stable ABI.

根據(jù) v 創(chuàng)建一個(gè) PyFloatObject 對(duì)象，失敗時(shí)返回 NULL。

double PyFloat_AsDouble(PyObject *pyfloat)?
Part of the Stable ABI.

返回一個(gè) C double 代表 pyfloat 的內(nèi)容。 如果 pyfloat 不是一個(gè) Python 浮點(diǎn)數(shù)對(duì)象但是具有 __float__() 方法，此方法將首先被調(diào)用，將 pyfloat 轉(zhuǎn)換成一個(gè)數(shù)點(diǎn)數(shù)。 如果 __float__() 未定義則將回退至 __index__()。 如果失敗，此方法將返回 -1.0，因此開(kāi)發(fā)者應(yīng)當(dāng)調(diào)用 PyErr_Occurred() 來(lái)檢查錯(cuò)誤。

在 3.8 版更改: 如果可用將使用 __index__()。

double PyFloat_AS_DOUBLE(PyObject *pyfloat)?

返回一個(gè) pyfloat 內(nèi)容的 C double 表示，但沒(méi)有錯(cuò)誤檢查。

PyObject *PyFloat_GetInfo(void)?
Return value: New reference. Part of the Stable ABI.

返回一個(gè) structseq 實(shí)例，其中包含有關(guān) float 的精度、最小值和最大值的信息。 它是頭文件 float.h 的一個(gè)簡(jiǎn)單包裝。

double PyFloat_GetMax()?
Part of the Stable ABI.

返回最大可表示的有限浮點(diǎn)數(shù) DBL_MAX 為 C double 。

double PyFloat_GetMin()?
Part of the Stable ABI.

返回最小可表示歸一化正浮點(diǎn)數(shù) DBL_MIN 為 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.

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).

3.11 新版功能.

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 and +0.0 produce the same bytes string.

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

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

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

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

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

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

double PyFloat_Unpack4(const unsigned char *p, int le)?

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

double PyFloat_Unpack8(const unsigned char *p, int le)?

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