diff --git a/uncompyle6/scanner.py b/uncompyle6/scanner.py
index d6651836..64b335db 100644
--- a/uncompyle6/scanner.py
+++ b/uncompyle6/scanner.py
@@ -21,6 +21,7 @@ scanner/ingestion module. From here we call various version-specific
 scanners, e.g. for Python 2.7 or 3.4.
 """
 
+from abc import ABC
 from array import array
 from collections import namedtuple
 from types import ModuleType
@@ -89,7 +90,7 @@ def long(num):
 CONST_COLLECTIONS = ("CONST_LIST", "CONST_SET", "CONST_DICT", "CONST_MAP")
 
 
-class Code(object):
+class Code:
     """
     Class for representing code-objects.
 
@@ -108,7 +109,7 @@ class Code(object):
         self._tokens, self._customize = scanner.ingest(co, classname, show_asm=show_asm)
 
 
-class Scanner:
+class Scanner(ABC):
     def __init__(self, version: tuple, show_asm=None, is_pypy=False):
         self.version = version
         self.show_asm = show_asm
@@ -293,6 +294,12 @@ class Scanner:
             return False
         return offset < self.get_target(offset)
 
+    def ingest(self, co, classname=None, code_objects={}, show_asm=None):
+        """
+        Code to tokenize disassembly. Subclasses must implement this.
+        """
+        raise NotImplementedError("This method should have been implemented")
+
     def prev_offset(self, offset: int) -> int:
         return self.insts[self.offset2inst_index[offset] - 1].offset
 
diff --git a/uncompyle6/scanners/scanner37.py b/uncompyle6/scanners/scanner37.py
index 894da02c..af4e8f5e 100644
--- a/uncompyle6/scanners/scanner37.py
+++ b/uncompyle6/scanners/scanner37.py
@@ -53,7 +53,7 @@ class Scanner37(Scanner37Base):
         if collection_type == "CONST_DICT":
             # constant dictionaries work via BUILD_CONST_KEY_MAP and
             # handle the values() like sets and lists.
-            # However the keys() are an LOAD_CONST of the keys.
+            # However, the keys() are an LOAD_CONST of the keys.
             # adjust offset to account for this
             count += 1
 
diff --git a/uncompyle6/scanners/scanner37base.py b/uncompyle6/scanners/scanner37base.py
index dc9804ed..e1c300d0 100644
--- a/uncompyle6/scanners/scanner37base.py
+++ b/uncompyle6/scanners/scanner37base.py
@@ -266,10 +266,9 @@ class Scanner37Base(Scanner):
                 if (
                     next_inst.opname == "LOAD_GLOBAL"
                     and next_inst.argval == "AssertionError"
-                    and inst.argval
+                    and inst.argval is not None
                 ):
-                    raise_idx = self.offset2inst_index[self.prev_op[inst.argval]]
-                    raise_inst = self.insts[raise_idx]
+                    raise_inst = self.get_inst(self.prev_op[inst.argval])
                     if raise_inst.opname.startswith("RAISE_VARARGS"):
                         self.load_asserts.add(next_inst.offset)
                     pass
@@ -286,7 +285,7 @@ class Scanner37Base(Scanner):
             # some backward jumps, are turned into forward jumps to another
             # "extended arg" backward jump to the same location.
             if inst.opname == "JUMP_FORWARD":
-                jump_inst = self.insts[self.offset2inst_index[inst.argval]]
+                jump_inst = self.get_inst(inst.argval)
                 if jump_inst.has_extended_arg and jump_inst.opname.startswith("JUMP"):
                     # Create a combination of the jump-to instruction and
                     # this one. Keep the position information of this instruction,