input: Write a function to find and print the largest value from a given list of numbers.
  assert get_max_value([2, 4, 1, 6]) == 6
  assert get_max_value([10, 5, 20, 15]) == 20
  assert get_max_value([0, -1, -5, -3]) == 0
  assert get_max_value([3]) == 3
  assert get_max_value([]) == None
output: def get_max_value(numbers):
      if not numbers:
          return None
      max_value = numbers[0]
      for num in numbers:
          if num > max_value:
              max_value = num
      return max_value