input: Write a function to search for a target value in a list and return its index. 
  assert search_value([1, 2, 3, 4, 5], 3) == 2
  assert search_value([10, 20, 30, 40], 25) == -1
  assert search_value([7, 8, 9, 10], 8) == 1
output: def search_value(lst, target):
      for index, value in enumerate(lst):
          if value == target:
              return index
      return -1