请详细解释以下Python代码的功能、逻辑流程以及每一行代码的作用。请确保解释通俗易懂，适合初学者理解。 def fibonacci(n): if n <= 0: return [] elif n == 1: return [0] sequence = [0, 1] while len(sequence) < n: next_val = sequence[-1] + sequence[-2] sequence.append(next_val) return sequence[:n]