object-oriented programming def __bisect_left(selfvalue)key self __key(valueleftright len(self __listwhile left rightmiddle (left right/ if self __key(self __list[middle]keyleft middle elseright middle return left this private method calculates the index position where the given value belongs in the listthat isthe index position where the value is (if it is in the list)or where it should go (if it isn' in the listit computes the comparison key for the given value using the sorted list' key functionand compares the comparison key with the computed comparison keys of the items that the method examines the algorithm used is binary search (also called binary chop)which has excellent performance even on very large lists--for exampleat most comparisons are required to find value' position in list of items compare this with plain unsorted list which uses linear search and needs an average of comparisonsand at worst comparisonsto find value in list of items def remove(selfvalue)index self __bisect_left(valueif index len(self __listand self __list[index=valuedel self __list[indexelseraise valueerror("{ remove( ) not in listformatself __class__ __name__)this method is used to remove the first occurrence of the given value it uses the sortedlist __bisect_left(method to find the index position where the value belongs and then tests to see whether that index position is within the list and that the item at that position is the same as the given value if the conditions are met the item is removedotherwisea valueerror exception is raised (which is what list remove(does in the same circumstancesdef remove_every(selfvalue)count index self __bisect_left(valuewhile (index len(self __listand self __list[index=value)python' bisect module provides the bisect bisect_left(function and some othersbut at the time of this writing none of the bisect module' functions can work with key function