input: Write a function to calculate the sum of a sequence of integers. If the sequence is empty, return 0.
  
  assert sum_sequence([1, 2, 3, 4, 5]) == 15
  assert sum_sequence([]) == 0
  assert sum_sequence([-1, 0, 1]) == 0
  assert sum_sequence([10, 20, 30]) == 60
  assert sum_sequence([5, -5, 5, -5]) == 0
output: def sum_sequence(sequence):
      return sum(sequence)