diff --git a/oemer/build_system.py b/oemer/build_system.py
index 3c0283b..d4394ce 100755
--- a/oemer/build_system.py
+++ b/oemer/build_system.py
@@ -72,17 +72,17 @@ class Key(enum.Enum):
 
 class Voice:
     def __init__(self) -> None:
-        self.id: int | Any = None
+        self.id: Union[int, None] = None
         self.note_ids: list[int] = []
-        self.stem_up: bool | Any = None
-        self.group_id: int | Any = None
-        self.x_center: float | Any = None
-        self.label: NoteType | Any = None
-        self.has_dot: bool | Any = None
-        self.group: int | Any = None
-        self.track: int | Any = None
-        self.duration: int | Any = None
-        self.rhythm_name: str | Any = None
+        self.stem_up: Union[bool, None] = None
+        self.group_id: Union[int, None] = None
+        self.x_center: Union[float, None] = None
+        self.label: NoteType = None  # type: ignore
+        self.has_dot: Union[bool, None] = None
+        self.group: Union[int, None] = None
+        self.track: Union[int, None] = None
+        self.duration: int = None  # type: ignore
+        self.rhythm_name: Union[str, None] = None
 
     def init(self) -> None:
         notes = layers.get_layer('notes')
@@ -107,8 +107,8 @@ def init(self) -> None:
                 notes[nid].force_set_label(self.label)
             notes[nid].has_dot = self.has_dot
 
-        self.rhythm_name = NOTE_TYPE_TO_RHYTHM[self.label]['name']
-        self.duration = NOTE_TYPE_TO_RHYTHM[self.label]['duration']
+        self.rhythm_name = NOTE_TYPE_TO_RHYTHM[self.label]['name']  # type: ignore
+        self.duration = NOTE_TYPE_TO_RHYTHM[self.label]['duration']  # type: ignore
         if self.has_dot:
             self.duration = round(self.duration * 1.5)  # type: ignore
 
@@ -121,18 +121,18 @@ def __repr__(self):
 class Measure:
     def __init__(self) -> None:
         self.symbols: List[Any] = []  # List of symbols
-        self.double_barline: bool | Any = None
+        self.double_barline: Union[bool, None] = None
         self.has_clef: bool = False
         self.clefs: list[Clef] = []
         self.voices: list[NoteGroup] = []
         self.sfns: list[Sfn] = []
         self.rests: list[Rest] = []
-        self.number: int | Any = None
-        self.at_beginning: bool | Any = None
-        self.group: int | Any = None
+        self.number: Union[int, None] = None
+        self.at_beginning: bool = None  # type: ignore
+        self.group: Union[int, None] = None
 
         self.time_slots: list[object] = []
-        self.slot_duras: np.ndarray | Any = None
+        self.slot_duras: np.ndarray = None  # type: ignore
 
     def add_symbols(self, symbols: Union[List[Union[Clef, Rest, Sfn]], List[Voice]]) -> None:
         self.symbols.extend(symbols)
@@ -188,7 +188,7 @@ def get_key(self) -> Key:
         # Count occurance
         sfn_counts = [0 for _ in range(track_nums)]
         for sfn in sfns_cands:
-            sfn_counts[sfn.track] += 1
+            sfn_counts[sfn.track] += 1  # type: ignore
 
         # Check validity
         all_same = all(ss.label==sfns_cands[0].label for ss in sfns_cands)  # All tracks have the same label.
@@ -466,7 +466,7 @@ def __init__(self, note: NoteHead, chord=False, voice=1, **kwargs):
         self.voice = voice
 
     def perform(self, parent_elem: Optional[Element] = None) -> Element:
-        clef_type = self.ctx.clefs[self.note.track].label
+        clef_type = self.ctx.clefs[self.note.track].label  # type: ignore
         chroma = get_chroma_pitch(self.note.staff_line_pos, clef_type)
         cur_sfn = self.ctx.sfn_state[chroma]
         if (self.note.sfn is not None) and (cur_sfn != self.note.sfn):
@@ -672,7 +672,7 @@ def gen_measures(self, group_container: Dict[int, List[Any]]) -> None:
         num = 1  # Measure count starts from 1 for MusicXML
         for grp, insts in group_container.items():
             self.measures[grp] = []
-            buffer: Any = []
+            buffer: List[Any] = []
             at_beginning = True
             double_barline = False
             for inst in insts:
diff --git a/oemer/dewarp.py b/oemer/dewarp.py
index 7969c61..84a44e3 100755
--- a/oemer/dewarp.py
+++ b/oemer/dewarp.py
@@ -11,7 +11,7 @@
 from oemer.morph import morph_open
 from oemer.logging import get_logger
 from numpy import ndarray
-from typing import List, Tuple, Any
+from typing import List, Tuple, Any, Union
 from typing_extensions import Self
 
 
@@ -20,7 +20,7 @@
 
 class Grid:
     def __init__(self) -> None:
-        self.id: int | Any = None
+        self.id: Union[int, None] = None
         self.bbox: list[int] | Any = None  # XYXY
         self.y_shift: int = 0
 
@@ -35,11 +35,11 @@ def height(self):
 
 class GridGroup:
     def __init__(self) -> None:
-        self.id: int | Any = None
-        self.reg_id: int | Any = None
+        self.id: Union[int, None] = None
+        self.reg_id: Union[int, None] = None
         self.bbox: list[int] | Any = None
         self.gids: list[int] = []
-        self.split_unit: int | Any = None
+        self.split_unit: int = None  # type: ignore
 
     @property
     def y_center(self):
diff --git a/oemer/note_group_extraction.py b/oemer/note_group_extraction.py
index 00aabbd..e6f4deb 100755
--- a/oemer/note_group_extraction.py
+++ b/oemer/note_group_extraction.py
@@ -15,7 +15,7 @@
     draw_bounding_boxes
 )
 from numpy import ndarray
-from typing import Dict, List, Tuple, Any
+from typing import Dict, List, Tuple, Any, Union
 
 # Globals
 grp_img: ndarray
@@ -25,16 +25,16 @@
 
 class NoteGroup:
     def __init__(self) -> None:
-        self.id: int | Any = None
+        self.id: Union[int, None] = None
         self.bbox: list[int] | Any = None
         self.note_ids: list[int] = []
         self.top_note_ids: list[int] = []  # For multi-melody cases
         self.bottom_note_ids: list[int] = []  # For multi-melody cases
-        self.stem_up: bool | Any = None
-        self.has_stem: bool | Any = None
-        self.all_same_type: bool | Any = None  # All notes are solid or hollow
-        self.group: int | Any = None
-        self.track: int | Any = None
+        self.stem_up: Union[bool, None] = None
+        self.has_stem: Union[bool, None] = None
+        self.all_same_type: Union[bool, None] = None  # All notes are solid or hollow
+        self.group: Union[int, None] = None
+        self.track: Union[int, None] = None
 
     @property
     def x_center(self) -> float:
diff --git a/oemer/notehead_extraction.py b/oemer/notehead_extraction.py
index 1800501..6b7d7ba 100755
--- a/oemer/notehead_extraction.py
+++ b/oemer/notehead_extraction.py
@@ -11,7 +11,7 @@
 from oemer.logging import get_logger
 from oemer.staffline_extraction import Staff
 from numpy import ndarray
-from typing import List, Tuple, Any
+from typing import List, Tuple, Any, Union
 
 # Globals
 nn_img: ndarray
@@ -37,24 +37,24 @@ class NoteType(enum.Enum):
 class NoteHead:
     def __init__(self) -> None:
         self.points: list[tuple] = []
-        self.pitch: int | Any = None
+        self.pitch: Union[int, None] = None
         self.has_dot: bool = False
         self.bbox: list[float] | Any = None  # XYXY
-        self.stem_up: bool | Any = None
-        self.stem_right: bool | Any = None
-        self.track: int | Any = None
-        self.group: int | Any = None
-        self.staff_line_pos: int | Any = None
-        self.invalid: bool | Any = False  # May be false positive
-        self.id: int | Any = None
-        self.note_group_id: int | Any = None
+        self.stem_up: Union[bool, None] = None
+        self.stem_right: Union[bool, None] = None
+        self.track: Union[int, None] = None
+        self.group: Union[int, None] = None
+        self.staff_line_pos: int = None  # type: ignore
+        self.invalid: Union[bool, None] = False  # May be false positive
+        self.id: Union[int, None] = None
+        self.note_group_id: Union[int, None] = None
         self.sfn: Any = None  # See symbols_extraction.py
 
         # Protected attributes
-        self._label: NoteType | Any = None
+        self._label: Union[NoteType, None] = None
 
     @property
-    def label(self) -> NoteType | Any:
+    def label(self) -> Union[NoteType, None]:
         if self.invalid:
             logger.warning(f"Note {self.id} is not a valid note.")
             return None
@@ -356,7 +356,7 @@ def assign_group_track(st: Staff) -> None:
         # Estimate position by the closeset center.
         pos_idx = np.argmin(np.abs(np.array(pos_cen)-cen_y))
         if 0 < pos_idx < len(pos_cen)-1:
-            nn.staff_line_pos = pos_idx
+            nn.staff_line_pos = int(pos_idx)
         elif pos_idx == 0:
             diff = abs(pos_cen[0] - cen_y)
             pos = round(diff / step)
@@ -392,7 +392,7 @@ def parse_stem_info(notes: List[NoteHead]) -> None:
         st_cen_x = np.mean(xi)
         cen_x = (box[0] + box[2]) / 2
         on_right = st_cen_x > cen_x
-        note.stem_right = on_right
+        note.stem_right = bool(on_right)
         # start_y = box[1] - offset
         # end_y = box[3] + offset
         # left_sum = np.sum(stems[start_y:end_y, box[0]-offset:box[2]])
diff --git a/oemer/symbol_extraction.py b/oemer/symbol_extraction.py
index c0fadbe..a08c005 100755
--- a/oemer/symbol_extraction.py
+++ b/oemer/symbol_extraction.py
@@ -25,8 +25,7 @@
 from typing import List, Union
 from typing import Tuple
 from numpy import ndarray
-from typing import Any
-from typing import Optional
+from typing import Any, Union
 
 # Globals
 global_cs: ndarray
@@ -60,9 +59,9 @@ class RestType(enum.Enum):
 class Clef:
     def __init__(self) -> None:
         self.bbox: list[int] | Any = None
-        self.track: int | Any = None
-        self.group: int | Any = None
-        self._label: ClefType | Any = None
+        self.track: Union[int, None] = None
+        self.group: Union[int, None] = None
+        self._label: ClefType = None  # type: ignore
 
     @property
     def label(self) -> ClefType:
@@ -84,11 +83,11 @@ def __repr__(self):
 class Sfn:
     def __init__(self) -> None:
         self.bbox: list[int] | Any = None
-        self.note_id: int | Any = None
-        self.is_key: bool | Any = None  # Whether is key or accidental
-        self.track: int | Any = None
-        self.group: int | Any = None
-        self._label: SfnType | Any = None
+        self.note_id: Union[int, None] = None
+        self.is_key: Union[bool, None] = None  # Whether is key or accidental
+        self.track: Union[int, None] = None
+        self.group: Union[int, None] = None
+        self._label: SfnType = None  # type: ignore
 
     @property
     def label(self) -> SfnType:
@@ -111,10 +110,10 @@ def __repr__(self):
 class Rest:
     def __init__(self) -> None:
         self.bbox: list[int] | Any = None
-        self.has_dot: bool | Any = None
-        self.track: int | Any = None
-        self.group: int | Any = None
-        self._label: RestType | Any = None
+        self.has_dot: Union[bool, None] = None
+        self.track: Union[int, None] = None
+        self.group: Union[int, None] = None
+        self._label: RestType = None  # type: ignore
 
     @property
     def label(self) -> RestType:
@@ -137,7 +136,7 @@ def __repr__(self):
 class Barline:
     def __init__(self) -> None:
         self.bbox: list[int] | Any = None
-        self.group: int | Any = None
+        self.group: Union[int, None] = None
 
     @property
     def x_center(self) -> float: