title: How do I make HTTP POST requests with grequests
body: <p>I tried the following:</p>
  
  <pre><code>import grequests
  
  urls = ['http://localhost/test', 'http://localhost/test']
  
  params = {'a':'b', 'c':'d'}
  rs = (grequests.post(u, params) for u in urls)
  grequests.map(rs)
  </code></pre>
  
  <p>But it says the following:</p>
  
  <pre><code>File "search.py", line 6, in &lt;genexpr&gt;
  rs = (grequests.post(u, params) for u in urls)
  TypeError: __init__() takes exactly 3 arguments (4 given)
  </code></pre>
  
  <p>I also need to pass the response to a callback for processing.</p>