diff --git a/src/kyupy/bench.py b/src/kyupy/bench.py
index fb80598..d678db3 100644
--- a/src/kyupy/bench.py
+++ b/src/kyupy/bench.py
@@ -74,14 +74,14 @@ GRAMMAR = r"""
     """
 
 
-def parse(text, name=None):
+def parse(text, name=None) -> Circuit:
     """Parses the given ``text`` as ISCAS89 bench code.
 
     :param text: A string with bench code.
     :param name: The name of the circuit. Circuit names are not included in bench descriptions.
     :return: A :class:`Circuit` object.
     """
-    return Lark(GRAMMAR, parser="lalr", transformer=BenchTransformer(name)).parse(text)
+    return Lark(GRAMMAR, parser="lalr", transformer=BenchTransformer(name)).parse(text) # type: ignore
 
 
 def load(file, name=None):
diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index ee49275..228ecd4 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -14,12 +14,12 @@ from __future__ import annotations
 
 from collections import deque, defaultdict
 import re
-from typing import Union
+from typing import Union, Any
 
 import numpy as np
 
 
-class GrowingList(list):
+class GrowingList[T](list[T]):
     def __setitem__(self, index, value):
         if value is None: self.has_nones = True
         if index == len(self): return super().append(value)
@@ -28,9 +28,13 @@ class GrowingList(list):
             self.has_nones = True
         super().__setitem__(index, value)
 
-    def __getitem__(self, index):
-        if isinstance(index, slice): return super().__getitem__(index)
-        return super().__getitem__(index) if index < len(self) else None
+    # Override __getitem__ to return None when reading beyond the list
+    # instead of throwing an exception. Type checker complains about the None return
+    # type, though. Probably not needed anyways.
+
+    #def __getitem__(self, index) -> list[T] | T | None:
+    #    if isinstance(index, slice): return super().__getitem__(index)
+    #    return super().__getitem__(index) if index < len(self) else None
 
     @property
     def free_idx(self):
@@ -155,7 +159,7 @@ class Line:
     Use the explicit case only if connections to specific pins are required.
     It may overwrite any previous line references in the connection list of the nodes.
     """
-    def __init__(self, circuit: Circuit, driver: Union[Node, tuple[Node, int]], reader: Union[Node, tuple[Node, int]]):
+    def __init__(self, circuit: Circuit, driver: Node | tuple[Node, None|int], reader: Node | tuple[Node, None|int]):
         self.circuit = circuit
         """The :class:`Circuit` object the line is part of.
         """
@@ -168,20 +172,20 @@ class Line:
         accessing it by :code:`my_data[l.index]` or simply by :code:`my_data[l]`.
         """
         if not isinstance(driver, tuple): driver = (driver, driver.outs.free_idx)
-        self.driver = driver[0]
+        self.driver: Node = driver[0]
         """The :class:`Node` object that drives this line.
         """
-        self.driver_pin = driver[1]
+        self.driver_pin = driver[1] if driver[1] is not None else self.driver.outs.free_idx
         """The output pin position of the driver node this line is connected to.
 
         This is the position in the list :py:attr:`Node.outs` of the driving node this line referenced from:
         :code:`self.driver.outs[self.driver_pin] == self`.
         """
         if not isinstance(reader, tuple): reader = (reader, reader.ins.free_idx)
-        self.reader = reader[0]
+        self.reader: Node = reader[0]
         """The :class:`Node` object that reads this line.
         """
-        self.reader_pin = reader[1]
+        self.reader_pin = reader[1] if reader[1] is not None else self.reader.ins.free_idx
         """The input pin position of the reader node this line is connected to.
 
         This is the position in the list :py:attr:`Node.ins` of the reader node this line referenced from:
@@ -203,8 +207,6 @@ class Line:
                 for i, l in enumerate(self.driver.outs): l.driver_pin = i
         if self.reader is not None: self.reader.ins[self.reader_pin] = None
         if self.circuit is not None: del self.circuit.lines[self.index]
-        self.driver = None
-        self.reader = None
         self.circuit = None
 
     def __index__(self):
@@ -309,7 +311,7 @@ class Circuit:
         """
         return self._locs(prefix, self.s_nodes)
 
-    def _locs(self, prefix, nodes):
+    def _locs(self, prefix, nodes:list[Node]) -> Node|list[Any]:  # can return list[list[...]]
         d_top = dict()
         for i, n in enumerate(nodes):
             if m := re.match(fr'({re.escape(prefix)}.*?)((?:[\d_\[\]])*$)', n.name):
@@ -324,7 +326,7 @@ class Circuit:
         def sorted_values(d): return [sorted_values(v) for k, v in sorted(d.items())] if isinstance(d, dict) else d
         l = sorted_values(d_top)
         while isinstance(l, list) and len(l) == 1: l = l[0]
-        return None if isinstance(l, list) and len(l) == 0 else l
+        return l #None if isinstance(l, list) and len(l) == 0 else l
 
     @property
     def stats(self):
diff --git a/src/kyupy/logic.py b/src/kyupy/logic.py
index 5cfbe92..c850e27 100644
--- a/src/kyupy/logic.py
+++ b/src/kyupy/logic.py
@@ -47,6 +47,7 @@ The functions in this module use the ``mv...`` and ``bp...`` prefixes to signify
 from collections.abc import Iterable
 
 import numpy as np
+from numpy.typing import DTypeLike
 
 from . import numba, hr_bytes
 
@@ -433,7 +434,7 @@ def unpackbits(a : np.ndarray):
     return np.unpackbits(a.view(np.uint8), bitorder='little').reshape(*a.shape, 8*a.itemsize)
 
 
-def packbits(a, dtype=np.uint8):
+def packbits(a, dtype:DTypeLike=np.uint8):
     """Packs the values of a boolean-valued array ``a`` along its last axis into bits.
 
     Similar to ``np.packbits``, but returns an array of given dtype and the shape of ``a`` with the last axis removed.
diff --git a/src/kyupy/verilog.py b/src/kyupy/verilog.py
index 39bd192..d6d6f33 100644
--- a/src/kyupy/verilog.py
+++ b/src/kyupy/verilog.py
@@ -258,7 +258,7 @@ GRAMMAR = r"""
     """
 
 
-def parse(text, tlib=KYUPY, branchforks=False):
+def parse(text, tlib=KYUPY, branchforks=False) -> Circuit:
     """Parses the given ``text`` as Verilog code.
 
     :param text: A string with Verilog code.
@@ -269,7 +269,7 @@ def parse(text, tlib=KYUPY, branchforks=False):
         (see :py:func:`~kyupy.sdf.DelayFile.interconnects()`).
     :return: A :py:class:`~kyupy.circuit.Circuit` object.
     """
-    return Lark(GRAMMAR, parser="lalr", transformer=VerilogTransformer(branchforks, tlib)).parse(text)
+    return Lark(GRAMMAR, parser="lalr", transformer=VerilogTransformer(branchforks, tlib)).parse(text) # type: ignore
 
 
 def load(file, tlib=KYUPY, branchforks=False):