given that strings are immutablea common question that arises is how we perform operations such inserting values rather than changing stringwe need to think of ways to build new string objects for the results we need for exampleif we wanted to insert word into our greetingwe could assign variable to the followingas this code showswe use the slice operator to split the string at index position and use to concatenate python never interprets the contents of string as number if we need to perform mathematical operations on stringwe need to first convert them to numeric typefor examplelists lists are probably the most used built-in data structures in python because they can be composed of any number of other data types they are simple representation of arbitrary objects like stringsthey are indexed by integers starting with zero the following table contains the most commonly used list methods and their descriptionsmethod description list(sreturns list of the sequence append(xappends element to the end of extend(xappends the list to count(xcounts the occurrence of in index( [start][stop]returns the smallest indexiwhere [ == can include optional start and stop index for the search