title: What does comma expression in for loop means in Python?
body: <p>I met the following loop header example:</p>
  
  <pre><code>for _, p in data.iterrows():
  </code></pre>
  
  <p>What does it mean? What is underscore and what is comma?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>iterrows is from here: <a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.iterrows.html" rel="nofollow">http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.iterrows.html</a></p>