decimal.py 文件源码

def _from_float(cls, f):
        if isinstance(f, int):                # handle integer inputs
            return cls(f)
        if not isinstance(f, float):
            raise TypeError("argument must be int or float.")
        if _math.isinf(f) or _math.isnan(f):
            return cls(repr(f))
        if _math.copysign(1.0, f) == 1.0:
            sign = 0
        else:
            sign = 1
        n, d = abs(f).as_integer_ratio()
        #k = d.bit_length() - 1
        k = _bit_length(d) - 1
        result = _dec_from_triple(sign, str(n*5**k), -k)
        if cls is Decimal:
            return result
        else:
            return cls(result)