title: what is the difference between data and params in requests?
body: <p>I am using <code>python requests</code> module, I send my params like this before:</p>
  
  <pre><code>requests.post(url=url, params=params)
  </code></pre>
  
  <p>but today, I find that I send my data like this, it fails, I change to this:</p>
  
  <pre><code>requests.post(url=url, data=params)
  </code></pre>
  
  <p>then it is ok, what is the difference between <code>data</code> and <code>params</code>?</p>
  
  <p>I observed that the request got a header <code>X-Requested-With:XMLHttpRequest</code>, is it because of this?</p>