In test_logpuzzle.py atest_path_from_string() add test cases. In logpuzzle.py path_from_string() revise regular expression and split to make test cases pass.
In conditionals change from implicit check for False (or None) to explicit check "is None".

References:
PEP-8 programming recommendations
"Comparisons to singletons like None should always be done with is or is not, never the equality operators...
Also, beware of writing if x when you really mean if x is not None"
http://www.python.org/dev/peps/pep-0008/

http://stackoverflow.com/questions/7816363/if-a-vs-if-a-is-not-none
In test_logpuzzle.py test_is_puzzle_url() add test cases.
In logpuzzle.py partially implement read_urls(). In test_logpuzzle.py test_read_urls() revise test to pass current behavior.