title: python not appending to each line in file in directory
body: <p>I am trying to append a string (<code>"testing123"</code>) to each line of every file in my current working directory (<code>cache/configs</code>). This is what I've done:</p>
  
  <pre><code>import os
  
  for file in os.listdir('cache/configs'):
      with open('cache/configs/'+file, "r") as f:
          lines = f.readlines()
          for line in lines:
              line = line+"testing123"
  </code></pre>
  
  <p>The command goes through without error, but nothing is changing. At face value my logic seems cogent. Where am I going wrong? Thanks.</p>
  
  <p>[Python version 3.6]</p>