fractions.py 文件源码

def from_decimal(cls, dec):
        """Converts a finite Decimal instance to a rational number, exactly."""
        from decimal import Decimal
        if isinstance(dec, numbers.Integral):
            dec = Decimal(int(dec))
        elif not isinstance(dec, Decimal):
            raise TypeError(
                "%s.from_decimal() only takes Decimals, not %r (%s)" %
                (cls.__name__, dec, type(dec).__name__))
        if not dec.is_finite():
            # Catches infinities and nans.
            raise TypeError("Cannot convert %s to %s." % (dec, cls.__name__))
        sign, digits, exp = dec.as_tuple()
        digits = int(''.join(map(str, digits)))
        if sign:
            digits = -digits
        if exp >= 0:
            return cls(digits * 10 ** exp)
        else:
            return cls(digits, 10 ** -exp)