부동 소수점 객체

type PyFloatObject

PyObject의 서브 형은 파이썬 부동 소수점 객체를 나타냅니다.

PyTypeObject PyFloat_Type
Part of the Stable ABI.

PyTypeObject 인스턴스는 파이썬 부동 소수점 형을 나타냅니다. 이것은 파이썬 계층에서 float와 같은 객체입니다.

int PyFloat_Check(PyObject *p)

인자가 PyFloatObjectPyFloatObject의 서브 형이면 참을 반환합니다. 이 함수는 항상 성공합니다.

int PyFloat_CheckExact(PyObject *p)

인자가 PyFloatObject이지만 PyFloatObject의 서브 형은 아니면 참을 반환합니다. 이 함수는 항상 성공합니다.

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

str의 문자열 값을 기반으로 PyFloatObject 객체를 만들거나, 실패하면 NULL.

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

v로부터 PyFloatObject 객체를 만들거나, 실패하면 NULL.

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

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.

버전 3.8에서 변경: 사용할 수 있으면 __index__()를 사용합니다.

double PyFloat_AS_DOUBLE(PyObject *pyfloat)

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

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

float의 정밀도, 최솟값, 최댓값에 관한 정보를 포함한 structseq 인스턴스를 돌려줍니다. 헤더 파일 float.h를 감싸는 얇은 래퍼입니다.

double PyFloat_GetMax()
Part of the Stable ABI.

Return the maximum representable finite float DBL_MAX as C double.

double PyFloat_GetMin()
Part of the Stable ABI.

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.

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).

버전 3.11에 추가.

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.