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
  assert sum_sequence([-1, -2, -3])==-6
  assert sum_sequence([10])==10
output: def sum_sequence(sequence):
      sum = 0
      for num in sequence:
          sum += num
      return sum