year-month-day formatting not working

Can't seem to figure out how to resolve this task! From what I understand this function will be receiving a string in the format of year-month-day or month-day-year by default and we are to create a directory within the current directory "./" with the year-month-day format.

I've created a simple check to see if the first part of the string is 4 digits ( a year ) or not. If it is not then we simply re-format the string into the correct pattern.

If the 1st part of the string is 4 digits then we can assume we have a year and the string is already in the year-month-day format.

TLDR; what's wrong with my logic? What am I not understanding about the question?

ERROR Shown: Bummer: Didn't find the right directory for a month-day-year date

and YES, I have tried to make multiple directories with both formats

import os

def create_daily_dir(datestr):
    ds = datestr.split("-")
    if len(ds[0]) != 4:
        # reformat month,day,year to year,month,day
        os.mkdir(f"{ds[2]}-{ds[0]}-{ds[1]}")
        return
    # else datestr is already year month day
    os.mkdir(datestr)