bpo-34215: Clarify IncompleteReadError message when "expected" is None (GH-21925)

Co-Authored-By: Tyler Bell <mrbell321@gmail.com>

Author: ZackerySpytz

Lib/asyncio/exceptions.py

@@ -34,8 +34,9 @@ class IncompleteReadError(EOFError):
  - expected: total number of expected bytes (or None if unknown)
  """
  def __init__(self, partial, expected):
+ r_expected = 'undefined' if expected is None else repr(expected)
  super().__init__(f'{len(partial)} bytes read on a total of '
- f'{expected!r} expected bytes')
+ f'{r_expected} expected bytes')
  self.partial = partial
  self.expected = expected
 

Lib/test/test_asyncio/test_streams.py

@@ -444,12 +444,14 @@ def test_readuntil_multi_chunks_1(self):
 
  def test_readuntil_eof(self):
  stream = asyncio.StreamReader(loop=self.loop)
- stream.feed_data(b'some dataAA')
+ data = b'some dataAA'
+ stream.feed_data(data)
  stream.feed_eof()
 
- with self.assertRaises(asyncio.IncompleteReadError) as cm:
+ with self.assertRaisesRegex(asyncio.IncompleteReadError,
+ 'undefined expected bytes') as cm:
  self.loop.run_until_complete(stream.readuntil(b'AAA'))
- self.assertEqual(cm.exception.partial, b'some dataAA')
+ self.assertEqual(cm.exception.partial, data)
  self.assertIsNone(cm.exception.expected)
  self.assertEqual(b'', stream._buffer)
 

Misc/NEWS.d/next/Library/2020-08-19-20-17-51.bpo-34215._Cv8c-.rst

@@ -0,0 +1,2 @@
+Clarify the error message for :exc:`asyncio.IncompleteReadError` when
+``expected`` is ``None``.