Fix for AttributeError when combining Bits objects with BitStreams.

Bug #329.

bitstring/bits.py

@@ -126,7 +126,7 @@ def __new__(cls: Type[TBits], auto: Optional[Union[BitsType, int]] = None, /, le
 
     @classmethod
     def _create_from_bitstype(cls: Type[TBits], auto: BitsType, /) -> TBits:
-        if isinstance(auto, Bits):
+        if isinstance(auto, cls):
             return auto
         b = super().__new__(cls)
         b._setauto_no_length_or_offset(auto)

release_notes.txt

@@ -11,6 +11,7 @@ A couple more minor bug fixes.
 * Initialising a bitstring from None now raises a TypeError rather than generating
   an empty bitstring. Bug #323.
 * Fixed performance regression for find/findall in some situations. Bug #326.
+* Fix for AttributeError bug when combining Bits with BitStream. Bug #329.
 
 -------------------------
 April 2024: version 4.2.1

tests/test_bitstream.py

@@ -4175,4 +4175,22 @@ def test_cache_with_length(self):
 def test_unpack_error():
     format_with_commas = ',bytes:2,,bytes:1,'
     dp = BitStream(hex='010203').unpack(fmt=format_with_commas)
-    assert dp == [b'\x01\x02', b'\x03']
+    assert dp == [b'\x01\x02', b'\x03']
+
+
+def test_add_pos_issue():
+    x = BitStream()
+    y = x + Bits('0xff')
+    assert x.pos == 0
+    assert y == '0xff'
+    z = x + bitstring.BitArray('0xff')
+    assert z == '0xff'
+    q = x + ConstBitStream('0xff')
+    assert q == '0xff'
+
+    xx = ConstBitStream()
+    yy = xx + Bits('0xff')
+    zz = xx + bitstring.BitArray('0xff')
+    qq = xx + BitStream('0xff')
+    assert yy == zz == qq == '0xff'
+