title: How to Change File Extension (.npy to .csv) in Python?
body: <p>I have 100 files with <code>.npy</code> extenstion. What should I do to convert all of them to <code>.csv</code> via loop <code>for</code>? </p>
  
  <p>Besides, how can I load all of them simultaneously to concatenate the arrays with each other to a new one?</p>
  
  <p>Regards</p>