Understanding how Binary Search Key works? 

A binary search key is used to quickly search for a specific value in a sorted array or list. The basic idea behind the binary search algorithm is to repeatedly divide the search interval in half until the value is found or the search interval is empty.

Here is an example of how to use a binary search key to search for a value in a sorted list in Python:

def binary_search(arr, x):
  low = 0
  high = len(arr) - 1
  while low <= high:
    mid = (low + high) // 2
    if arr[mid] == x:
      return mid
    elif arr[mid] < x:
      low = mid + 1
    else:
      high = mid - 1
  return -1

arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
x = 6
result = binary_search(arr, x)
if result != -1:
  print("The element is present at index", str(result))
else:
  print("The element is not present in the array.")

In this example, the function binary_search() takes two parameters: an array arr and a value x to search for. It uses two variables low and high to keep track of the search interval. It then repeatedly divides the search interval in half by updating the low and high variables until the value is found or the search interval is empty. The function returns the index of the element if it is present, and -1 if it is not present in the array.

It’s worth noting that the binary search algorithm can only be applied to a sorted data, the data should be in ascending or descending order. Also, the time complexity of the binary search algorithm is O(log n) which makes it efficient for large data sets.