Assignment 1
Obtain the sub-string excluding the first and last characters from the string s. 

Assignment 2
Check if s is a valid name of a day of the week. Change the solution to this problem, to include forms like, SAT, SATURDAY, Saturday and Sat. 

Assignment 3
Replace the [dot] with . in email 

Assignment 4
From the email_str that we generated, change the separator to be a semicolon instead of a comma. 

Assignment 5
Given a string s = "this is a string", how will you change it to "this isn't a list" ?
Given the string "F.R.I.E.N.D.S" in s, obtain the string "friends".