fix codec overriding

[komuw]

see:

naz/tests/test_codec.py

Lines 177 to 232 in 8b1ec3d

	@skip(
	"""
	TODO:fix this. It does not work.
	Note: Encodings are first looked up in the registry's cache.
	thus if you call `register_codecs` and then call it again with different
	codecs, the second codecs may not take effect.
	ie; codecs.lookup(encoding) will return the first codecs since they were stored
	in the cache.
	There doesn't appear to be away to clear codec cache at runtime.
	see: https://docs.python.org/3/library/codecs.html#codecs.lookup
	This test passes when called in isolation but it fails when all tests are ran together.
	This is because, when all tests are ran together; `naz.codec.register_codecs` will already have
	been called and registered the inbuilt codecs. So when this test runs,it tries to override
	an already registered codec. And then it calls `codecs.lookup()`. However,
	lookup will return the codec that is in the cache which is the inbuilt codecs instead of the ones
	we just tried to register in this test.
	We should look if to find a way to clear the codec cache at runtime.
	There's a C api for that `_PyCodec_Forget`
	https://sourcegraph.com/github.com/python/cpython@3.8/-/blob/Python/codecs.c#L193
	We need to figure out how to call it or find other alternatives.
	I have sent an email to Marc-Andre Lemburg asking for advice.
	"""
	)
	def test_codec_overriding(self):
	"""
	tests that users can be able to override an inbuilt codec
	with their own implementation.
	"""
	class OverridingCodec(codecs.Codec):
	# All the methods have to be staticmethods because they are passed to `codecs.CodecInfo`
	@staticmethod
	def encode(input, errors="strict"):
	return codecs.utf_8_encode(input, errors)
	@staticmethod
	def decode(input, errors="strict"):
	return codecs.utf_8_decode(input, errors)
	custom_codecs = {
	"gsm0338": codecs.CodecInfo(
	name="gsm0338", encode=OverridingCodec.encode, decode=OverridingCodec.decode,
	),
	}
	# register, this will override inbuilt `gsm0338` codec with a custom one.
	naz.codec.register_codecs(custom_codecs)
	new_codec = codecs.lookup("gsm0338")
	self.assertNotEqual(new_codec.encode, naz.codec.GSM7BitCodec.encode)
	self.assertNotEqual(new_codec.decode, naz.codec.GSM7BitCodec.decode)
	self.assertEqual(new_codec.encode, OverridingCodec.encode)
	self.assertEqual(new_codec.decode, OverridingCodec.decode)

I had asked Marc-Andre Lemburg(author of codec module in python) whether you can override an inbuilt codec, and his reply:

It's not really supported to override builtin codecs via a search
function. The only way is to monkey patch the encodings package
module implementing the codec and then only if you manage to
implement this patching before the codec gets used for the first
time, since the codec subsystem uses a cache for codecs to improve
performance.

Note that the codec search function registry is mainly meant to
*add* new codecs, not to override existing ones.

This was via email.

We should re-architect based on this new info.