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([10, 20, 30])==60 
  assert sum_sequence([0, -1, 1])==0
  assert sum_sequence([])==0
output: def sum_sequence(sequence): 
    sum = 0 
    for num in sequence: 
      sum += num 
    return sum