input: Write a python function to implement a queue class and perform operations like enqueue, dequeue, and check if the queue is empty.
  assert q.isEmpty() == True
  q.enqueue(4)
  q.enqueue('dog')
  q.enqueue(True)
  assert q.size() == 3
  assert q.peek() == 4
  assert q.dequeue() == 4
  assert q.size() == 2
output: class Queue:
      def __init__(self):
          self.items = []
      
      def isEmpty(self):
          return len(self.items) == 0
      
      def enqueue(self, item):
          self.items.insert(0, item)
      
      def dequeue(self):
          if not self.isEmpty():
              return self.items.pop()
      
      def size(self):
          return len(self.items)
      
      def peek(self):
          if not self.isEmpty():
              return self.items[-1]
  
  # Example usage:
  q = Queue()
  assert q.isEmpty() == True
  q.enqueue(4)
  q.enqueue('dog')
  q.enqueue(True)
  assert q.size() == 3
  assert q.peek() == 4
  assert q.dequeue() == 4
  assert q.size() == 2