GeezerVison is showing docs.python.org — Floating-Point Objects
Floating-Point Objects¶
-
type PyFloatObject¶
This subtype of PyObject represents a Python floating-point object.
-
PyTypeObject PyFloat_Type¶
- Part of the Stable ABI.
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)¶
- Return value: New reference. Part of the Stable ABI.
Create a PyFloatObject object based on the string value in str, or
NULL on failure.
-
PyObject *PyFloat_FromDouble(double v)¶
- Return value: New reference. Part of the Stable ABI.
Create a PyFloatObject object from v, or NULL 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 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.
-
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 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).
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:
-
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.
© Copyright 2001-2026, Python Software Foundation.
This page is licensed under the Python Software Foundation License Version 2.
Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License.
See History and License for more information.
The Python Software Foundation is a non-profit corporation.
Please donate.
Last updated on Oct 26, 2026 (15:00 UTC).
Found a bug?
Created using Sphinx 8.2.3.
|