title: pandas isin append unhashable type: 'list' error
body: <p>I ran out of idea on how to add new items to filter list in pandas.</p>
  
  <p>Example:</p>
  
  <pre><code>OldProducts = ProductInfo[ProductInfo['MerchantID'].isin(['A store', 'B store'])]
  
  OldProductsId = list(OldProducts.PID.unique())
  
  OldProductsId2 = ['VayjE7nrDl', 'BYbcAAuV0r', 'hu2y8rYIbN', 'YXELEovcwK']
  
  OldProductsId.append(OldProductsId2)
  
  DetailProductInfo = DetailProductInfo [~DetailProductInfo ['PID'].isin(OldProductsId)]
  </code></pre>
  
  <p>The error is like this:
  TypeError: unhashable type: 'list'</p>