Utilize string formatting in Python to convert date expression into a standardized format.
The task involves creating a function for a calendar program. This function needs to ensure that the representation of months and days is always in a two-digits format. In cases when the month or the day is a single digit, the function should add a '0' in front. ### Parameters - `y`: An integer that represents the year. - `m`: An integer that represents the month. - `d`: An integer that represents the day. ### Return Value - The function should return the date in the following format: 'yyyy-mm-dd'. If the month or the day is a single digit, a leading '0' should be added. ### Examples ```python format_date(2018,2,18) # ➞ '2018-02-18' format_date(2019,6,7) # ➞ '2019-06-07' format_date(2020,10,1) # ➞ '2020-10-01' format_date(2020,10,10) # ➞ '2020-10-10' ```