using WindowsError in a try/except. Only add WindowsError to the list of
exceptions to catch when we are actually running on Windows.
Additionally, add a call that was left out in test_posixpath.
Thanks Amaury, Antoine, and Jason.
Added Windows support for os.symlink when run on Windows 6.0 or greater,
aka Vista. Previous Windows versions will raise NotImplementedError
when trying to symlink.
Includes numerous test updates and additions to test_os, including
a symlink_support module because of the fact that privilege escalation
is required in order to run the tests to ensure that the user is able
to create symlinks. By default, accounts do not have the required
privilege, so the escalation code will have to be exposed later (or
documented on how to do so). I'll be following up with that work next.
Note that the tests use ctypes, which was agreed on during the PyCon
language summit.
This required moving the class from importlib/abc.py into
importlib/_bootstrap.py and jiggering some code to work better with the class.
This included changing how the file finder worked to better meet import
semantics. This also led to fixing importlib to handle the empty string from
sys.path as import currently does (and making me wish we didn't support that
instead just required people to insert '.' instead to represent cwd).
It also required making the new set_data abstractmethod create
any needed subdirectories implicitly thanks to __pycache__ (it was either this
or grow the SourceLoader ABC to gain an 'exists' method and either a mkdir
method or have set_data with no data arg mean to create a directory).
Lastly, as an optimization the file loaders cache the file path where the
finder found something to use for loading (this is thanks to having a
sourceless loader separate from the source loader to simplify the code and
cut out stat calls).
Unfortunately test_runpy assumed a loader would always work for a module, even
if you changed from underneath it what it was expected to work with. By simply
dropping the previous loader in test_runpy so the proper loader can be returned
by the finder fixed the failure.
At this point importlib deviates from import on two points:
1. The exception raised when trying to import a file is different (import does
an explicit file check to print a special message, importlib just says the path
cannot be imported as if it was just some module name).
2. the co_filename on a code object is not being set to where bytecode was
actually loaded from instead of where the marshalled code object originally
came from (a solution for this has already been agreed upon on python-dev but has
not been implemented yet; issue8611).
