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