input: Write a python function to implement a queue with enqueue, dequeue, and peek methods.
  assert q.peek() == None
  q.enqueue(1)
  q.enqueue(2)
  q.enqueue(3)
  assert q.dequeue() == 1
  assert q.peek() == 2
  assert q.dequeue() == 2
  assert q.dequeue() == 3
  assert q.dequeue() == None
output: class Queue:
      def __init__(self):
          self.queue = []
  
      def enqueue(self, item):
          self.queue.append(item)
  
      def dequeue(self):
          if not self.queue:
              return None
          return self.queue.pop(0)
  
      def peek(self):
          if not self.queue:
              return None
          return self.queue[0]
  
  q = Queue()
  assert q.peek() == None
  q.enqueue(1)
  q.enqueue(2)
  q.enqueue(3)
  assert q.dequeue() == 1
  assert q.peek() == 2
  assert q.dequeue() == 2
  assert q.dequeue() == 3
  assert q.dequeue() == None