Cropping the strings in a list : <p>I have a list which the super-cropped version looks like this:</p>

<pre><code>b=['5:18:00',
 '5:19:00',
 '5:20:00',
 '5:21:00',
 '11:31:00',
 '11:32:00',
 '11:33:00',
 '0:01:00',
 '0:02:00',
 '0:03:00']
</code></pre>

<p>I want to keep the hours, and eliminate the rest. </p>

<p>Your help is appreciated. </p>
