Python Colon(:) in list index
<p>I'm new to Python. I see <code>:</code> used in list index especially when it's associated with functional calls, for e.g., python 2.7 document suggests that <code>lists.append</code> translates to <code>a[len(a):] = [x]</code>. Why do one have to suffix <code>len(a)</code> with a colon?</p>

<p>I understand that : is used to identify keys in dictionary. Thanks in advance for the help.</p>
