Why are filename underscores better than hyphens
<p>From <a href="http://homepage.mac.com/s_lott/books/python/BuildingSkillsinPython.pdf">Building Skills in Python</a>:</p>

<p>"A file name like exercise_1.py is better than the name execise-1.py. We can run both programs equally well from the command line, but the name with the hyphen limits our ability to write larger and more sophisticated programs."</p>

<p>Why?</p>
