title: Python reads incremental text
body: <p>I saw a piece of code, as follows：</p>
  <pre><code>with open(‘text.txt’,‘r’)as fp:
    
      while True:
          data_line=fp.readline()
  
          if data_line:
              print(data_line)
  </code></pre>
  <p>writing data in txt，and all the time python will keep outputting.</p>
  <p>I think this code is great.
  But I don't quite understand the line <code>if data_line:</code></p>
  <p>I hope someone can explain it, thanks.</p>