$($a$)]$ Define a function called repeat$\_$letters that takes a string and a number $n$ as two parameters and prints the string with every letter repeated $n$ times.

Sample input$/$Output:

$$ print$($repeat$\_$letters$("$medipol$",3))$

"mmmeeedddiiipppooolll"

$($b$)$

Define a function called find index which takes as argument a word and a letter. It will return the index of the second occurrence of the letter in the given word.

Sample input$/$Output:

$$ print$($find$\_$index$("$welcomehome$","$e$"))$

$6$

$($c$)$ Define a function called list$\_$unique that takes a string str as an input, checks all letters of the string, and constructs a list that contains the list of character that appear in str$.$ This list should not contain any duplicates.

Sample input$/$Output:

print$($list$\_$unique$("$ankara$"))$

$[\text{'}a\text{'},\text{'}n\text{'},\text{'}k\text{'},\text{'}r\text{'}]$

$($d$)$

$\text{'}$ Write a function called ngrams$\_$list that takes a string and a number $n$ and return the $n-$grams of the this string as a list

Sample input$/$Output:

$[["$co$","$om$","$mp$","$pu$","$ut$","$te$","$er$"]$

$2$