input: Write a function to identify the largest number in the given list. If the list is empty, return None.
  assert identify_largest_number([1000, 506, 299, 620, 35])==1000
  assert identify_largest_number([9, 8, 7, 6, 5])==9
  assert identify_largest_number([-1, 0, -2, -3])==0
  assert identify_largest_number([5])==5
  assert identify_largest_number([])==None
output: def identify_largest_number(lst):
      if not lst:
          return None
      return max(lst)