If we are not sure that the list is sorted, we could use the built-in min()
function, to find the element which has the minimum distance from the specified number.
>>> min(myList, key=lambda x:abs(x-myNumber))
4
Note that it also works with dicts with int keys, like {1: "a", 2: "b"}
. This method takes O(n) time.
If the list is already sorted, or you could pay the price of sorting the array once only, use the bisection method illustrated in @Lauritz’s answer which only takes O(log n) time (note however checking if a list is already sorted is O(n) and sorting is O(n log n).)