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([0, -1, 2, -3, 4]) == 2
  assert sum_sequence([]) == 0
  assert sum_sequence([-1, -2, -3, -4, -5]) == -15
  assert sum_sequence([10]) == 10
output: def sum_sequence(sequence):
    sum = 0
    for num in sequence:
      sum += num
    return sum