python · ilevkivskyi · Sep 5, 2019 · Sep 5, 2019 · Sep 5, 2019
diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
@@ -2103,8 +2103,9 @@ def dangerous_comparison(self, left: Type, right: Type,
             right = remove_optional(right)
         if (original_container and has_bytes_component(original_container) and
                 has_bytes_component(left)):
-            # We need to special case bytes, because both 97 in b'abc' and b'a' in b'abc'
-            # return True (and we want to show the error only if the check can _never_ be True).
+            # We need to special case bytes and bytearray, because 97 in b'abc', b'a' in b'abc',
+            # b'a' in bytearray(b'abc') etc. all return True (and we want to show the error only
+            # if the check can _never_ be True).
             return False
         if isinstance(left, Instance) and isinstance(right, Instance):
             # Special case some builtin implementations of AbstractSet.
@@ -4136,11 +4137,12 @@ def custom_equality_method(typ: Type) -> bool:
 
 
 def has_bytes_component(typ: Type) -> bool:
-    """Is this the builtin bytes type, or a union that contains it?"""
+    """Is this one of builtin byte types, or a union that contains it?"""
     typ = get_proper_type(typ)
     if isinstance(typ, UnionType):
         return any(has_bytes_component(t) for t in typ.items)
-    if isinstance(typ, Instance) and typ.type.fullname() == 'builtins.bytes':
+    if isinstance(typ, Instance) and typ.type.fullname() in {'builtins.bytes',
+                                                             'builtins.bytearray'}:
         return True
     return False
 

diff --git a/test-data/unit/check-expressions.test b/test-data/unit/check-expressions.test
@@ -2059,6 +2059,13 @@ x in b'abc'
 [builtins fixtures/primitives.pyi]
 [typing fixtures/typing-full.pyi]
 
+[case testStrictEqualityByteArraySpecial]
+# flags: --strict-equality
+b'abc' in bytearray(b'abcde')
+bytearray(b'abc') in b'abcde'  # OK on Python 3
+[builtins fixtures/primitives.pyi]
+[typing fixtures/typing-full.pyi]
+
 [case testStrictEqualityNoPromotePy3]
 # flags: --strict-equality
 'a' == b'a'  # E: Non-overlapping equality check (left operand type: "Literal['a']", right operand type: "Literal[b'a']")

diff --git a/test-data/unit/check-type-promotion.test b/test-data/unit/check-type-promotion.test
@@ -23,7 +23,7 @@ f(1)
 
 [case testPromoteBytearrayToByte]
 def f(x: bytes) -> None: pass
-f(bytearray())
+f(bytearray(b''))
 [builtins fixtures/primitives.pyi]
 
 [case testNarrowingDownFromPromoteTargetType]

diff --git a/test-data/unit/fixtures/primitives.pyi b/test-data/unit/fixtures/primitives.pyi
@@ -29,7 +29,11 @@ class bytes(Sequence[int]):
     def __iter__(self) -> Iterator[int]: pass
     def __contains__(self, other: object) -> bool: pass
     def __getitem__(self, item: int) -> int: pass
-class bytearray: pass
+class bytearray(Sequence[int]):
+    def __init__(self, x: bytes) -> None: pass
+    def __iter__(self) -> Iterator[int]: pass
+    def __contains__(self, other: object) -> bool: pass
+    def __getitem__(self, item: int) -> int: pass
 class tuple(Generic[T]): pass
 class function: pass
 class ellipsis: pass