Python codes are required:

$1.$Implement a function that accepts as input a list of tuples, where each tuple includes the name of a student and the grade corresponding to it$,$ and returns a new list of tuples arranged in descending order in terms of grades.

$2.$ Implement a function that takes a string as input and returns the largest substring that does not contain repeated characters $(eg,$ for $"$ abcabcbb $",$ it will return $"abc").$

$3.$ Implement a function that accepts a string as input and returns all recursive substrings $($e$.$g$.$ for "ababa" $("$a$","$b$","$a$","$b$","$a$",$ "aba"$).$

$4.$ Implement a function that accepts two strings as input and returns the longest common sequence of characters.

$5.$ Implement a function which accepts a string as its input and returns the minimum number of characters that must be completed to make it recursive $(eg"$ abcde $"$ requires $4$

characters$).$