Autodetect parse() format

[dwinston]

Addresses #981

• Use rdflib.util.guess_format to guess and try to apply format based on file extension
• Log warning if assumed XML(not guessed from file extension) and cannot parse
• Add tests

Close #981

[coveralls]

Coverage increased (+0.03%) to 75.793% when pulling b5fa8ec on dwinston:autodetect-parse-format into 037ea51 on RDFLib:master.

[dwinston]

@tgbugs what do you think? I hope I've resolved your concerns.

[tgbugs]

Under what circumstances are you seeing these errors? I'm guessing when source.file.name is None for the TypeError and probably ... when not hasattr(source, 'file')? If that is the case then an explicit test (if statement) for the presence and non-Noneness of the values would be much clearer here.

[dwinston]

@tgbugs I've adopted your suggestion for more of a look-before-you-leap approach with an explicit if-statement guard, ensuring that source.file.name is an accessible path and is a string before attempting a call to guess_format.

[nicholascar]

@dwinston please merge in master branch and address conflicts since a whole host of changes were recently merged in to remove Python 2 code. This will trigger a re-checking of the code by Travis. Then we can redress the comments from @tgbugs

[dwinston]

@dwinston please merge in master branch and address conflicts since a whole host of changes were recently merged in to remove Python 2 code. This will trigger a re-checking of the code by Travis. Then we can redress the comments from @tgbugs

Sure, will do.

[dwinston]

@nicholascar merged in master, and I hope I addressed the comments from @tgbugs with my last commit. Also, I thought I'd note here that the more recent PR #1064 is an alternative solution to the same underlying issue.