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On Wed, 15 Jun 2016 at 12:12 Koos Zevenhoven <k7hoven@gmail.com> wrote:

>> if isinstance(filename, os.PathLike):

By the way, regarding the line of code above, is there a convention
regarding whether implementing some protocol/interface requires
registering with (or inheriting from) the appropriate ABC for it to
work in all situations. IOW, in this case, is it sufficient to
implement \_\_fspath\_\_ to make your type pathlike? Is there a conscious
trend towards requiring the ABC?

ABCs like os.PathLike can override \_\_subclasshook\_\_ so that registration isn't required (see https://hg.python.org/cpython/file/default/Lib/os.py#l1136). So registration is definitely good to do to be explicit that you're trying to meet an ABC, but it isn't strictly required.