input: Write a function to implement a binary search algorithm in Python that takes a sorted list of numbers and a target value, and returns the index of the target value if it is found in the list, otherwise returns -1.
  
  def binary_search(nums, val):
      low = 0
      high = len(nums) - 1
      
      while low <= high:
          mid = (low + high) // 2
          if nums[mid] == val:
              return mid
          elif nums[mid] > val:
              high = mid - 1
          else:
              low = mid + 1
      return -1
  
  assert binary_search([3, 4, 5, 6, 7, 8, 9], 8)==5
  assert binary_search([1, 2, 3, 4, 5], 6)==-1
  assert binary_search([], 7)==-1
  assert binary_search([1, 3, 5, 7, 9], 3)==1
  assert binary_search([2, 4, 6, 8, 10], 10)==4
output: def binary_search(nums, val):
      low = 0
      high = len(nums) - 1
      
      while low <= high:
          mid = (low + high) // 2
          if nums[mid] == val:
              return mid
          elif nums[mid] > val:
              high = mid - 1
          else:
              low = mid + 1
      return -1