File warning instead of fail if stdout does not have encoding

[throwable-one]

According to Python manual sys.stdout should have encoding.
Unfortunatelly, nose monekypatches it with StringIO with out of encoding.

See: nose-devs/nose#1065

Its nose fault, not win-unicode-console fault. But can we please do

def check_encodings():
	try:
		if sys.stdin.encoding != sys.stdout.encoding:
			# raise RuntimeError("sys.stdin.encoding != sys.stdout.encoding, readline hook doesn't know, which one to use to decode prompt")

			warnings.warn("sys.stdin.encoding == {!r}, whereas sys.stdout.encoding == {!r}, readline hook consumer may assume they are the same".format(sys.stdin.encoding, sys.stdout.encoding),
				RuntimeWarning, stacklevel=3)
	except AttributeError:
		warnings.warn("stdin or stdout does not have encoding")

?

[throwable-one]

Could be fixed by removing check_encoding as suggested here #36

[Drekin]

Does the solution of #36 work for you? Also thank you for the pull request, but I'll probably add something like

no_encoding = object()
stdin_encoding = getattr(sys.stdin, "encoding", no_encoding)
if stdin_encoding is no_encoding: warn()

So, stdin and stdout cases are distinguished. Also, there is probably a reason to use stacklevel=3 in the warn, so I would use it here also.

[GadgetSteve]

Note that I have also had an issue with this problem when using py2exe on code that uses this module. (It has a Blackhole class that substitutes for sys.stdout and doesn't have an encoding property) In my case I found that getattr(sys.stdout, "encoding", None) worked fine.

[Drekin]

@GadgetSteve Is a warning ok for you?

[GadgetSteve]

@Drekin A clear warning is always better than a crash.