bpo-31722: Update codecs.IncrementalDecoder to use __subclasshook__

Lib/codecs.py

@@ -7,8 +7,10 @@
 
 """
 
+import abc
 import builtins
 import sys
+import _collections_abc
 
 ### Registry and builtin stateless codec functions
 
@@ -251,7 +253,7 @@ def getstate(self):
     def setstate(self, state):
         self.buffer = state or ""
 
-class IncrementalDecoder(object):
+class IncrementalDecoder(abc.ABC):
     """
     An IncrementalDecoder decodes an input in multiple steps. The input can
     be passed piece by piece to the decode() method. The IncrementalDecoder
@@ -300,6 +302,13 @@ def setstate(self, state):
         setstate((b"", 0)) must be equivalent to reset().
         """
 
+    @classmethod
+    def __subclasshook__(cls, C):
+        if issubclass(C, _io.IncrementalNewlineDecoder):
+            return _collections_abc._check_methods(C, "decode", "reset",
+                                                   "getstate", "setstate")
+        return NotImplemented
+
 class BufferedIncrementalDecoder(IncrementalDecoder):
     """
     This subclass of IncrementalDecoder can be used as the baseclass for an
@@ -1110,6 +1119,11 @@ def make_encoding_map(decoding_map):
 if _false:
     import encodings
 
+try:
+    import _io
+    IncrementalDecoder.register(_io.IncrementalNewlineDecoder)
+except ImportError:
+    pass
 ### Tests
 
 if __name__ == '__main__':

Lib/test/test_io.py

@@ -4177,6 +4177,9 @@ def test_check_encoding_errors(self):
         proc = assert_python_failure('-X', 'dev', '-c', code)
         self.assertEqual(proc.rc, 10, proc)
 
+    def test_subclass_of_codecs_incremental_decoder(self):
+        self.assertTrue(self.io.IncrementalNewlineDecoder,
+                        codecs.IncrementalDecoder)
 
 class CMiscIOTest(MiscIOTest):
     io = io

Misc/NEWS.d/next/Library/2019-10-09-02-57-03.bpo-31722.r1mkRa.rst

@@ -0,0 +1,2 @@
+Update :class:`codecs.IncrementalDecoder` to use :meth:`__subclasshook__` method.
+(Contributed by Dong-hee Na in :issue:`31722`.)