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