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