diff --git a/capa/features/extractors/elf.py b/capa/features/extractors/elf.py
index d5c187dc..4fed06dc 100644
--- a/capa/features/extractors/elf.py
+++ b/capa/features/extractors/elf.py
@@ -92,17 +92,18 @@ class Shdr:
 
 
 class ELF:
-    def __init__(self, f):
+    def __init__(self, f: BinaryIO):
         self.f = f
 
-        self.bitness: int = None
-        self.endian: str = None
-        self.e_phentsize: int = None
-        self.e_phnum: int = None
-        self.e_shentsize: int = None
-        self.e_shnum: int = None
-        self.phbuf = None
-        self.shbuf = None
+        # these will all be initialized in `_parse()`
+        self.bitness: int = 0
+        self.endian: str = ""
+        self.e_phentsize: int = 0
+        self.e_phnum: int = 0
+        self.e_shentsize: int = 0
+        self.e_shnum: int = 0
+        self.phbuf: bytes = b""
+        self.shbuf: bytes = b""
 
         self._parse()
 
@@ -512,13 +513,14 @@ class ABITag:
 
 
 class PHNote:
-    def __init__(self, endian, buf):
+    def __init__(self, endian: str, buf: bytes):
         self.endian = endian
         self.buf = buf
 
-        self.type_: int = None
-        self.descsz: int = None
-        self.name: str = None
+        # these will be initialized in `_parse()`
+        self.type_: int = 0
+        self.descsz: int = 0
+        self.name: str = ""
 
         self._parse()
 
@@ -560,13 +562,14 @@ class PHNote:
 
 
 class SHNote:
-    def __init__(self, endian, buf):
+    def __init__(self, endian: str, buf: bytes):
         self.endian = endian
         self.buf = buf
 
-        self.type_: int = None
-        self.descsz: int = None
-        self.name: str = None
+        # these will be initialized in `_parse()`
+        self.type_: int = 0
+        self.descsz: int = 0
+        self.name: str = ""
 
         self._parse()
 
diff --git a/capa/features/extractors/ida/helpers.py b/capa/features/extractors/ida/helpers.py
index a333f064..5c997f69 100644
--- a/capa/features/extractors/ida/helpers.py
+++ b/capa/features/extractors/ida/helpers.py
@@ -5,7 +5,7 @@
 # Unless required by applicable law or agreed to in writing, software distributed under the License
 #  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and limitations under the License.
-from typing import Any, Dict, Tuple, Iterator
+from typing import Any, Dict, Tuple, Iterator, Optional
 
 import idc
 import idaapi
@@ -36,7 +36,7 @@ def find_byte_sequence(start: int, end: int, seq: bytes) -> Iterator[int]:
 
 
 def get_functions(
-    start: int = None, end: int = None, skip_thunks: bool = False, skip_libs: bool = False
+    start: Optional[int] = None, end: Optional[int] = None, skip_thunks: bool = False, skip_libs: bool = False
 ) -> Iterator[FunctionHandle]:
     """get functions, range optional
 
@@ -287,7 +287,7 @@ def is_frame_register(reg: int) -> bool:
     return reg in (idautils.procregs.sp.reg, idautils.procregs.bp.reg)
 
 
-def get_insn_ops(insn: idaapi.insn_t, target_ops: Tuple[Any] = None) -> idaapi.op_t:
+def get_insn_ops(insn: idaapi.insn_t, target_ops: Optional[Tuple[Any]] = None) -> idaapi.op_t:
     """yield op_t for instruction, filter on type if specified"""
     for op in insn.ops:
         if op.type == idaapi.o_void:
diff --git a/capa/features/extractors/viv/basicblock.py b/capa/features/extractors/viv/basicblock.py
index 6341ec3a..9848bec0 100644
--- a/capa/features/extractors/viv/basicblock.py
+++ b/capa/features/extractors/viv/basicblock.py
@@ -31,7 +31,7 @@ def interface_extract_basic_block_XXX(f: FunctionHandle, bb: BBHandle) -> Iterat
     yields:
       (Feature, Address): the feature and the address at which its found.
     """
-    ...
+    raise NotImplementedError
 
 
 def _bb_has_tight_loop(f, bb):
diff --git a/capa/features/extractors/viv/function.py b/capa/features/extractors/viv/function.py
index 64671711..cf1df527 100644
--- a/capa/features/extractors/viv/function.py
+++ b/capa/features/extractors/viv/function.py
@@ -27,7 +27,7 @@ def interface_extract_function_XXX(fh: FunctionHandle) -> Iterator[Tuple[Feature
     yields:
       (Feature, Address): the feature and the address at which its found.
     """
-    ...
+    raise NotImplementedError
 
 
 def extract_function_calls_to(fhandle: FunctionHandle) -> Iterator[Tuple[Feature, Address]]:
diff --git a/capa/features/extractors/viv/insn.py b/capa/features/extractors/viv/insn.py
index ae106c31..738c69a7 100644
--- a/capa/features/extractors/viv/insn.py
+++ b/capa/features/extractors/viv/insn.py
@@ -44,7 +44,7 @@ def interface_extract_instruction_XXX(
     yields:
       (Feature, Address): the feature and the address at which its found.
     """
-    ...
+    raise NotImplementedError
 
 
 def get_imports(vw):