title: Unable to convert back changed date time to timeStamp in python
body: <p>I want to convert  <code>timestamps</code> to <code>dates</code> and truncate <code>minute</code> and <code>seconds</code>,then, convert it back to <code>timestamps</code>. I know I can do that with some mathematical algorithm like  <code>timestamps/60</code> or <code>timestamps/3600</code>, but I want to use <code>Python</code> provided functions. My code is like below. I tried two methods:</p>
  
  <pre><code>for timeStamp in lineTimeStamps:
      #first try 
      day1=datetime.datetime.\
          fromtimestamp(float(timeStamp)).strftime("%Y-%m-%d %H")
      timestamp1 = time.mktime(day1)
      #second try 
      day2=datetime.datetime.\
          fromtimestamp(float(timeStamp)).\
          replace( minute=0, second=0, microsecond=0).timetuple()
      timestamp2 = time.mktime(day2)
  </code></pre>
  
  <p>In <code>timestamp1 = time.mktime(day1)</code>, I got the error like:</p>
  
  <blockquote>
    <p>TypeError: Tuple or struct_time argument required</p>
  </blockquote>
  
  <p>In <code>timestamp2 = time.mktime(day2)</code>, I got the error like:</p>
  
  <blockquote>
    <p>OverflowError: mktime argument out of range</p>
  </blockquote>
  
  <p>How can I convert it back to <code>timestamps</code>? </p>