diff --git a/masque/file/dxf.py b/masque/file/dxf.py
index 4c30124..7f1ad41 100644
--- a/masque/file/dxf.py
+++ b/masque/file/dxf.py
@@ -127,7 +127,7 @@ def readfile(
         filename: Union[str, pathlib.Path],
         *args,
         **kwargs,
-        ) -> Tuple[Pattern, Dict[str, Any]]:
+        ) -> Tuple[Dict[str, Pattern], Dict[str, Any]]:
     """
     Wrapper for `dxf.read()` that takes a filename or path instead of a stream.
 
diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index c54cc88..5eb9896 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -19,7 +19,7 @@ Notes:
  * Creation/modification/access times are set to 1900-01-01 for reproducibility.
 """
 from typing import List, Any, Dict, Tuple, Callable, Union, Iterable, Optional
-from typing import Sequence, BinaryIO, Mapping
+from typing import Sequence, BinaryIO, Mapping, cast
 import re
 import io
 import mmap
@@ -298,7 +298,7 @@ def _gref_to_mref(ref: klamath.library.Reference) -> Ref:
         repetition = Grid(a_vector=a_vector, b_vector=b_vector,
                           a_count=a_count, b_count=b_count)
 
-    ref = Ref(
+    mref = Ref(
         target=ref.struct_name.decode('ASCII'),
         offset=offset,
         rotation=numpy.deg2rad(ref.angle_deg),
@@ -307,7 +307,7 @@ def _gref_to_mref(ref: klamath.library.Reference) -> Ref:
         annotations=_properties_to_annotations(ref.properties),
         repetition=repetition,
         )
-    return ref
+    return mref
 
 
 def _gpath_to_mpath(gpath: klamath.library.Path, raw_mode: bool) -> Path:
@@ -341,7 +341,7 @@ def _boundary_to_polygon(boundary: klamath.library.Boundary, raw_mode: bool) ->
 
 
 def _mrefs_to_grefs(refs: List[Ref]) -> List[klamath.library.Reference]:
-    refs = []
+    grefs = []
     for ref in refs:
         if ref.target is None:
             continue
@@ -370,9 +370,9 @@ def _mrefs_to_grefs(refs: List[Ref]) -> List[klamath.library.Reference]:
                 mag=ref.scale,
                 properties=properties,
                 )
-            refs.append(aref)
+            grefs.append(aref)
         elif rep is None:
-            ref = klamath.library.Reference(
+            sref = klamath.library.Reference(
                 struct_name=encoded_name,
                 xy=rint_cast([ref.offset]),
                 colrow=None,
@@ -381,7 +381,7 @@ def _mrefs_to_grefs(refs: List[Ref]) -> List[klamath.library.Reference]:
                 mag=ref.scale,
                 properties=properties,
                 )
-            refs.append(ref)
+            grefs.append(sref)
         else:
             new_srefs = [
                 klamath.library.Reference(
@@ -394,8 +394,8 @@ def _mrefs_to_grefs(refs: List[Ref]) -> List[klamath.library.Reference]:
                     properties=properties,
                     )
                 for dd in rep.displacements]
-            refs += new_srefs
-    return refs
+            grefs += new_srefs
+    return grefs
 
 
 def _properties_to_annotations(properties: Dict[int, bytes]) -> annotations_t:
@@ -635,17 +635,17 @@ def load_libraryfile(
     if is_gzipped(path):
         if mmap:
             logger.info('Asked to mmap a gzipped file, reading into memory instead...')
-            base_stream = gzip.open(path, mode='rb')
-            stream = io.BytesIO(base_stream.read())
+            gz_stream = gzip.open(path, mode='rb')
+            stream = io.BytesIO(gz_stream.read())       # type: ignore
         else:
-            base_stream = gzip.open(path, mode='rb')
-            stream = io.BufferedReader(base_stream)
+            gz_stream = gzip.open(path, mode='rb')
+            stream = io.BufferedReader(gz_stream)       # type: ignore
     else:
-        base_stream = open(path, mode='rb')
         if mmap:
-            stream = mmap.mmap(base_stream.fileno(), 0, access=mmap.ACCESS_READ)
+            base_stream = open(path, mode='rb', buffering=0)
+            stream = mmap.mmap(base_stream.fileno(), 0, access=mmap.ACCESS_READ)    # type: ignore
         else:
-            stream = io.BufferedReader(base_stream)
+            stream = open(path, mode='rb')
     return load_library(stream, full_load=full_load)
 
 
diff --git a/masque/file/oasis.py b/masque/file/oasis.py
index 4785f55..543700c 100644
--- a/masque/file/oasis.py
+++ b/masque/file/oasis.py
@@ -484,8 +484,10 @@ def _placement_to_ref(placement: fatrec.Placement, lib: fatamorgana.OasisLayout)
     assert(not isinstance(placement.repetition, fatamorgana.ReuseRepetition))
     xy = numpy.array((placement.x, placement.y))
     mag = placement.magnification if placement.magnification is not None else 1
+
     pname = placement.get_name()
-    name = pname if isinstance(pname, int) else pname.string
+    name: Union[int, str] = pname if isinstance(pname, int) else pname.string       # TODO deal with referenced names
+
     annotations = properties_to_annotations(placement.properties, lib.propnames, lib.propstrings)
     if placement.angle is None:
         rotation = 0
@@ -506,7 +508,7 @@ def _placement_to_ref(placement: fatrec.Placement, lib: fatamorgana.OasisLayout)
 def _refs_to_placements(
         refs: List[Ref],
         ) -> List[fatrec.Placement]:
-    refs = []
+    placements = []
     for ref in refs:
         if ref.target is None:
             continue
@@ -517,7 +519,7 @@ def _refs_to_placements(
 
         offset = rint_cast(ref.offset + rep_offset)
         angle = numpy.rad2deg(ref.rotation + extra_angle) % 360
-        ref = fatrec.Placement(
+        placement = fatrec.Placement(
             name=ref.target,
             flip=mirror_across_x,
             angle=angle,
@@ -528,8 +530,8 @@ def _refs_to_placements(
             repetition=frep,
             )
 
-        refs.append(ref)
-    return refs
+        placements.append(placement)
+    return placements
 
 
 def _shapes_to_elements(
diff --git a/masque/shapes/path.py b/masque/shapes/path.py
index f177d07..ec76bbd 100644
--- a/masque/shapes/path.py
+++ b/masque/shapes/path.py
@@ -1,4 +1,4 @@
-from typing import List, Tuple, Dict, Optional, Sequence, Any
+from typing import List, Tuple, Dict, Optional, Sequence, Any, cast
 import copy
 from enum import Enum
 
@@ -365,7 +365,7 @@ class Path(Shape, metaclass=AutoSlots):
         x_min = rotated_vertices[:, 0].argmin()
         if not is_scalar(x_min):
             y_min = rotated_vertices[x_min, 1].argmin()
-            x_min = x_min[y_min]
+            x_min = cast(Sequence, x_min)[y_min]
         reordered_vertices = numpy.roll(rotated_vertices, -x_min, axis=0)
 
         width0 = self.width / norm_value
diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index 0a05e78..252cf22 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -1,4 +1,4 @@
-from typing import List, Dict, Optional, Sequence, Any
+from typing import List, Dict, Optional, Sequence, Any, cast
 import copy
 
 import numpy
@@ -374,7 +374,7 @@ class Polygon(Shape, metaclass=AutoSlots):
         x_min = rotated_vertices[:, 0].argmin()
         if not is_scalar(x_min):
             y_min = rotated_vertices[x_min, 1].argmin()
-            x_min = x_min[y_min]
+            x_min = cast(Sequence, x_min)[y_min]
         reordered_vertices = numpy.roll(rotated_vertices, -x_min, axis=0)
 
         # TODO: normalize mirroring?
diff --git a/masque/traits/annotatable.py b/masque/traits/annotatable.py
index 3fca734..b10b042 100644
--- a/masque/traits/annotatable.py
+++ b/masque/traits/annotatable.py
@@ -6,6 +6,9 @@ from ..utils import annotations_t
 from ..error import MasqueError
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 T = TypeVar('T', bound='Annotatable')
 I = TypeVar('I', bound='AnnotatableImpl')
 
@@ -33,7 +36,7 @@ class AnnotatableImpl(Annotatable, metaclass=ABCMeta):
     """
     Simple implementation of `Annotatable`.
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _annotations: annotations_t
     """ Dictionary storing annotation name/value pairs """
@@ -46,7 +49,7 @@ class AnnotatableImpl(Annotatable, metaclass=ABCMeta):
         return self._annotations
 
     @annotations.setter
-    def annotations(self, annotations: annotations_t):
+    def annotations(self, annotations: annotations_t) -> None:
         if not isinstance(annotations, dict):
             raise MasqueError(f'annotations expected dict, got {type(annotations)}')
         self._annotations = annotations
diff --git a/masque/traits/layerable.py b/masque/traits/layerable.py
index c3c6aba..eae2de4 100644
--- a/masque/traits/layerable.py
+++ b/masque/traits/layerable.py
@@ -4,6 +4,9 @@ from abc import ABCMeta, abstractmethod
 from ..utils import layer_t
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 T = TypeVar('T', bound='Layerable')
 I = TypeVar('I', bound='LayerableImpl')
 
@@ -50,7 +53,7 @@ class LayerableImpl(Layerable, metaclass=ABCMeta):
     """
     Simple implementation of Layerable
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _layer: layer_t
     """ Layer number, pair, or name """
diff --git a/masque/traits/positionable.py b/masque/traits/positionable.py
index b7548cb..58c225c 100644
--- a/masque/traits/positionable.py
+++ b/masque/traits/positionable.py
@@ -9,6 +9,9 @@ from numpy.typing import NDArray, ArrayLike
 from ..error import MasqueError
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 T = TypeVar('T', bound='Positionable')
 I = TypeVar('I', bound='PositionableImpl')
 
@@ -85,7 +88,7 @@ class PositionableImpl(Positionable, metaclass=ABCMeta):
     """
     Simple implementation of Positionable
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _offset: NDArray[numpy.float64]
     """ `[x_offset, y_offset]` """
@@ -108,7 +111,7 @@ class PositionableImpl(Positionable, metaclass=ABCMeta):
 
         if val.size != 2:
             raise MasqueError('Offset must be convertible to size-2 ndarray')
-        self._offset = val.flatten()
+        self._offset = val.flatten()        # type: ignore
 
     '''
     ---- Methods
diff --git a/masque/traits/repeatable.py b/masque/traits/repeatable.py
index 9f032b7..4ec9147 100644
--- a/masque/traits/repeatable.py
+++ b/masque/traits/repeatable.py
@@ -4,6 +4,9 @@ from abc import ABCMeta, abstractmethod
 from ..error import MasqueError
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 if TYPE_CHECKING:
     from ..repetition import Repetition
 
@@ -55,7 +58,7 @@ class RepeatableImpl(Repeatable, metaclass=ABCMeta):
     """
     Simple implementation of `Repeatable`
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _repetition: Optional['Repetition']
     """ Repetition object, or None (single instance only) """
diff --git a/masque/traits/rotatable.py b/masque/traits/rotatable.py
index add9686..c8b1479 100644
--- a/masque/traits/rotatable.py
+++ b/masque/traits/rotatable.py
@@ -10,6 +10,9 @@ from ..error import MasqueError
 from ..utils import is_scalar, rotation_matrix_2d
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 T = TypeVar('T', bound='Rotatable')
 I = TypeVar('I', bound='RotatableImpl')
 P = TypeVar('P', bound='Pivotable')
@@ -43,7 +46,7 @@ class RotatableImpl(Rotatable, metaclass=ABCMeta):
     """
     Simple implementation of `Rotatable`
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _rotation: float
     """ rotation for the object, radians counterclockwise """
diff --git a/masque/traits/scalable.py b/masque/traits/scalable.py
index ec87c69..2216945 100644
--- a/masque/traits/scalable.py
+++ b/masque/traits/scalable.py
@@ -5,6 +5,9 @@ from ..error import MasqueError
 from ..utils import is_scalar
 
 
+_empty_slots = ()     # Workaround to get mypy to ignore intentionally empty slots for superclass
+
+
 T = TypeVar('T', bound='Scalable')
 I = TypeVar('I', bound='ScalableImpl')
 
@@ -36,7 +39,7 @@ class ScalableImpl(Scalable, metaclass=ABCMeta):
     """
     Simple implementation of Scalable
     """
-    __slots__ = ()
+    __slots__ = _empty_slots
 
     _scale: float
     """ scale factor for the entity """