so far用于现在完成时
up to now用于一般将来时那by far呢by far（最，显然：到达极为明显的程度）
She is by far the best executive in the company.
她目前是公司中最为优秀的决策人
She is the best by far/She is by far the best.
她显然是最好的

by far用于比较级之后时，比较级前不带冠词
如:better by far or by far the better