input: Write a function to search for a value in an array and return the index of the first occurrence of this value. If the value is not found, return -1.
  assert find_index([2, 5, 9, 15], 5)==1
  assert find_index([2, 5, 9, 15], 15)==3
  assert find_index([2, 5, 9, 15], 7)==-1
  assert find_index([], 5)==-1
output: def find_index(arr, value):
      try:
          return arr.index(value)
      except ValueError:
          return -1