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