浮點數（Floating Point）物件
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PyFloatObject

   This subtype of "PyObject" represents a Python floating point
   object.

PyTypeObject PyFloat_Type

   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".

int PyFloat_CheckExact(PyObject *p)

   Return true if its argument is a "PyFloatObject", but not a subtype
   of "PyFloatObject".

PyObject* PyFloat_FromString(PyObject *str)
    *Return value: New reference.*

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

PyObject* PyFloat_FromDouble(double v)
    *Return value: New reference.*

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

double PyFloat_AsDouble(PyObject *pyfloat)

   返回一个 C "double" 代表 *pyfloat* 的内容。 如果 *pyfloat* 不是一个
   Python 浮点数对象但是具有 "__float__()" 方法，此方法将首先被调用，
   将 *pyfloat* 转换成一个数点数。 如果 "__float__()" 未定义则将回退至
   "__index__()"。 如果失败，此方法将返回 "-1.0"，因此开发者应当调用
   "PyErr_Occurred()" 来检查错误。

   3.8 版更變: 如果可用将使用 "__index__()"。

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.*

   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()

   Return the maximum representable finite float *DBL_MAX* as C
   "double".

double PyFloat_GetMin()

   Return the minimum normalized positive float *DBL_MIN* as C
   "double".

int PyFloat_ClearFreeList()

   Clear the float free list. Return the number of items that could
   not be freed.
