statistics.py 文件源码

def _exact_ratio(x):
    """Convert Real number x exactly to (numerator, denominator) pair.

    >>> _exact_ratio(0.25)
    (1, 4)

    x is expected to be an int, Fraction, Decimal or float.
    """
    try:
        try:
            # int, Fraction
            return (x.numerator, x.denominator)
        except AttributeError:
            # float
            try:
                return x.as_integer_ratio()
            except AttributeError:
                # Decimal
                try:
                    return _decimal_to_ratio(x)
                except AttributeError:
                    msg = "can't convert type '{}' to numerator/denominator"
                    raise TypeError(msg.format(type(x).__name__)) from None
    except (OverflowError, ValueError):
        # INF or NAN
        if __debug__:
            # Decimal signalling NANs cannot be converted to float :-(
            if isinstance(x, Decimal):
                assert not x.is_finite()
            else:
                assert not math.isfinite(x)
        return (x, None)


# FIXME This is faster than Fraction.from_decimal, but still too slow.