title: Python modifying csv column by increments
body: <p>First off, I apologize for the terrible title; I didn't know how to summarize my problem. Okay, so here's a the first few lines of my .csv file. The first column is the timestamp. The program I'm getting this data from samples 24 times per second, so there are 24 rows that start with 15:40:15, 24 that start with 15:40:16, and so on. Instead of 24 rows with the same timestamp, I want the timestamp to increase increments of 1/24 seconds, or .042 seconds. So 15:40:15.042, 15:40:15.084, etc.</p>
  
  <p>Another problem is that there aren't 24 rows for the first second, because we start in the middle of the second. For example, there are only 13 15:40:14 rows. For those it would preferably count backwards from 15:40:15.000 and subtract .042 seconds for every row.</p>
  
  <p>How can I do this in Python? Thanks in advance!  </p>
  
  <pre><code>CPUtime,Displacement Into Surface,Load On Sample,Time On Sample,Raw Load,Raw Displacement
  15:40:14,-990.210561,-0.000025,1.7977E+308,-115.999137,-989.210000
  15:40:14,-989.810561,-0.000025,1.7977E+308,-115.999105,-988.810000
  15:40:14,-989.410561,-0.000025,1.7977E+308,-115.999073,-988.410000
  15:40:14,-989.010561,-0.000025,1.7977E+308,-115.999041,-988.010000
  15:40:14,-988.590561,-0.000025,1.7977E+308,-115.999007,-987.590000
  15:40:14,-988.170561,-0.000025,1.7977E+308,-115.998974,-987.170000
  15:40:14,-987.770561,-0.000025,1.7977E+308,-115.998942,-986.770000
  15:40:14,-987.310561,-0.000025,1.7977E+308,-115.998905,-986.310000
  15:40:14,-986.870561,-0.000025,1.7977E+308,-115.998870,-985.870000
  15:40:14,-986.430561,-0.000025,1.7977E+308,-115.998834,-985.430000
  15:40:14,-985.990561,-0.000025,1.7977E+308,-115.998799,-984.990000
  15:40:14,-985.570561,-0.000025,1.7977E+308,-115.998766,-984.570000
  15:40:14,-985.170561,-0.000025,1.7977E+308,-115.998734,-984.170000
  15:40:15,-984.730561,-0.000025,1.7977E+308,-115.998698,-983.730000
  15:40:15,-984.310561,-0.000025,1.7977E+308,-115.998665,-983.310000
  15:40:15,-983.890561,-0.000025,1.7977E+308,-115.998631,-982.890000
  15:40:15,-983.490561,-0.000025,1.7977E+308,-115.998599,-982.490000
  15:40:15,-983.090561,-0.000025,1.7977E+308,-115.998567,-982.090000
  </code></pre>