FloatingPoint Objects¶

PyTypeObject PyFloat_Type¶
 Part of the Stable ABI.
This instance of
PyTypeObject
represents the Python floatingpoint type. This is the same object asfloat
in the Python layer.

int PyFloat_Check(PyObject *p)¶
Return true if its argument is a
PyFloatObject
or a subtype ofPyFloatObject
. This function always succeeds.

int PyFloat_CheckExact(PyObject *p)¶
Return true if its argument is a
PyFloatObject
, but not a subtype ofPyFloatObject
. This function always succeeds.

PyObject *PyFloat_FromString(PyObject *str)¶
 Return value: New reference. Part of the Stable ABI.
Create a
PyFloatObject
object based on the string value in str, orNULL
on failure.

PyObject *PyFloat_FromDouble(double v)¶
 Return value: New reference. Part of the Stable ABI.
Create a
PyFloatObject
object from v, orNULL
on failure.

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 floatingpoint 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 returns1.0
upon failure, so one should callPyErr_Occurred()
to check for errors.Changed in version 3.8: 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)¶
 Return value: New reference. Part of the Stable ABI.
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()¶
 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 platformindependent way to store floatingpoint 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 2byte format is identical to the IEEE 754 binary16 halfprecision format, the 4byte format (32bit) is identical to the IEEE 754 binary32 single precision format, and the 8byte 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 nonIEEE platforms with more precision, or larger dynamic range, than IEEE 754 supports, not all values can be packed; on nonIEEE platforms with less precision, or smaller dynamic range, not all values can be unpacked. What happens in such cases is partly accidental (alas).
Added in version 3.11.
Pack functions¶
The pack routines write 2, 4 or 8 bytes, starting at p. le is an
int argument, nonzero if you want the bytes string in littleendian
format (exponent last, at p+1
, p+3
, or p+6
p+7
), zero if you
want bigendian 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 nonIEEE 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 halfprecision 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, nonzero if the bytes string is in littleendian format
(exponent last, at p+1
, p+3
or p+6
and p+7
), zero if bigendian
(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 nonIEEE 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 halfprecision 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.