input: Write a function to calculate the sum of a sequence of integers. The function should take in a list of integers as input and return the sum of all the integers in the list. If the input list is empty, the function should return 0.
  
  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([-1, -2, -3, -4, -5])==-15
  assert sum_sequence([])==0
output: def sum_sequence(sequence):
      sum = 0
      for num in sequence:
          sum += num
      return sum