      "        while source.peek() is not None:\n",
      "            destination.push(source.pop())\n",
      "\n",
      "    def enqueue(self, data):\n",
      "        if self.left_stack.is_empty() and not self.right_stack.is_empty():\n",
      "            self.shift_stacks(self.right_stack, self.left_stack)\n",
      "        self.left_stack.push(data)\n",
      "\n",
      "    def dequeue(self):\n",
      "        if self.right_stack.is_empty() and not self.left_stack.is_empty():\n",
      "            self.shift_stacks(self.left_stack, self.right_stack)\n",
 
</s> remove     "        if self.right_stack.is_empty() and not self.left_stack.is_empty():\n",
    "            self.shift_stacks(self.left_stack, self.right_stack)\n",
 </s> add     "        self.shift_stacks(self.left_stack, self.right_stack)\n", </s> remove     "* If the right stack is empty and the the left stack is not empty\n",
 </s> add     "* If the left stack is not empty\n", </s> remove     "* If the left stack is empty and the right stack is not empty\n",
 </s> add     "* If right stack is not empty\n", </s> remove     "* Do you expect the methods to be enqueue and dequeue?\n",
 </s> add     "* Do we expect the methods to be enqueue and dequeue?\n", </s> remove     "* Do you expect the methods to be enqueue and dequeue?\n",
 </s> add     "* Do we expect the methods to be enqueue and dequeue?\n",
    "        self.shift_stacks(self.right_stack, self.left_stack)\n",
      "        while source.peek() is not None:\n",
      "            destination.push(source.pop())\n",
      "\n",
      "    def enqueue(self, data):\n",
    "        self.shift_stacks(self.right_stack, self.left_stack)\n",
    "        self.shift_stacks(self.right_stack, self.left_stack)\n",
      "        self.left_stack.push(data)\n",
      "\n",
      "    def dequeue(self):\n",
      "        if self.right_stack.is_empty() and not self.left_stack.is_empty():\n",
      "            self.shift_stacks(self.left_stack, self.right_stack)\n",
keep keep keep keep replace replace keep keep keep keep keep
 Polish queue from stacks challenge and solution (#74)

Update constraints, algorithm discussion, and code. 
stacks_queues/queue_from_stacks/queue_from_stacks_solution.ipynb