title: Create an array with consecutive seconds - strptime - KeyError : 0
body: <p>I am trying to create an array that converts minutes, seconds, and milliseconds to seconds and adds them consecutively. </p>
  
  <p>I have a df with a timestamp as follows:</p>
  
  <pre><code>        Time        Temp.
  0   14:12:58:8230    135
  1   14:12:59:0190    185
  2   14:12:59:2150    138
  </code></pre>
  
  <p>I do the following to retrieve the data and access all the Timestamp column with <code>datetime.strptime</code> and make the array. But, when running it, I seem to have a <code>KeyError : 0</code>. </p>
  
  <pre><code>elapsed_x = []
  tmp_1 = []
  
  for i in range (0, len(df)): 
      tmp = datetime.strptime(df.Time[i], '%H:%M:%S:%f') 
      tmp_ms = tmp.microsecond
      tmp_s = tmp.second
      tmp_min  = tmp.minute
      tmp_1.append(tmp_min*60 + tmp_s + tmp_ms/1000000)
  
  for i in range (0, len(df)):     
      elapsed_x.append(tmp_1[i]-tmp_1[0])
  </code></pre>
  
  <p>What am I doing wrong?</p>