diff --git a/xdis/cross_dis.py b/xdis/cross_dis.py
index d85b7d93..775d2b78 100644
--- a/xdis/cross_dis.py
+++ b/xdis/cross_dis.py
@@ -15,7 +15,7 @@
 #  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 # Here, we are more closely modeling Python's ``dis`` module organization.
-# However, it appears that Python names and code has copied a bit heavily from
+# However, it appears that Python's names and code have been copied a bit heavily from
 # earlier versions of xdis (and without attribution).
 
 from typing import List
@@ -116,7 +116,7 @@ def findlabels_pre_310(code, opc):
     return offsets
 
 
-# For the `co_lines` attribute we want to emit the full form, omitting
+# For the `co_lines` attribute, we want to emit the full form, omitting
 # the (350, 360, No line number) and empty entries.
 
 NO_LINE_NUMBER = -128
@@ -188,9 +188,9 @@ def instruction_size(op, opc):
     """For a given opcode, `op`, in opcode module `opc`,
     return the size, in bytes, of an `op` instruction.
 
-    This is the size of the opcode (1 byte) and any operand it has. In
-    Python before version 3.6 this will be either 1 or 3 bytes.  In
-    Python 3.6 or later, it is 2 bytes or a "word"."""
+    This is the size of the opcode (one byte) and any operand it has.
+    In Python before version 3.6, this will be either 1 or 3 bytes.
+    In Python 3.6 or later, it is 2 bytes: a "word"."""
     if op < opc.HAVE_ARGUMENT:
         return 2 if opc.version_tuple >= (3, 6) else 1
     else:
diff --git a/xdis/disasm.py b/xdis/disasm.py
index 33f4ec7e..227b32c2 100644
--- a/xdis/disasm.py
+++ b/xdis/disasm.py
@@ -156,7 +156,7 @@ def disco(
         is_graal=is_graal,
     )
 
-    # store final output stream for case of error
+    # Store final output stream when there is an error.
     real_out = out or sys.stdout
 
     if co.co_filename and asm_format != "xasm":
@@ -195,7 +195,7 @@ def disco_loop(
     """Disassembles a queue of code objects. If we discover
     another code object which will be found in co_consts, we add
     the new code to the list. Note that the order of code discovery
-    is in the order of first encountered which is not amenable for
+    is in the order of first encountered that is not amenable for
     the format used by a disassembler where code objects should
     be defined before using them in other functions.
     However, this is not recursive and will overall lead to less
@@ -282,8 +282,8 @@ def disco_loop_asm_format(opc, version_tuple, co, real_out, fn_name_map, all_fns
             mapped_name = code_uniquify(basename, co.co_code)
             co_name = mapped_name
             if mapped_name in fn_name_map:
-                # We can have two lambda's created that are the same
-                # but have different line numbers
+                # We can have two lambdas created that are the same
+                # but have different line numbers.
                 mapped_name += f"_{str(co.co_firstlineno)}"
         fn_name_map[mapped_name] = basename
         co.co_name = mapped_name
@@ -314,12 +314,12 @@ def disassemble_file(
     show_source=False,
 ):
     """
-    disassemble Python byte-code file (.pyc)
+    Disassemble Python byte-code file (.pyc).
 
     If given a Python source file (".py") file, we'll
     try to find the corresponding compiled object.
 
-    If that fails we'll compile internally for the Python version currently running
+    If that fails, we'll compile internally for the Python version currently running.
     """
     pyc_filename = None
     try:
@@ -400,11 +400,9 @@ def _test():
     argc = len(sys.argv)
     if argc == 1:
         if xdis.PYTHON3:
-            fn = __file__
+            disassemble_file(__file__)
         else:
-            sys.stderr.write(
-                "usage: %s [-|CPython compiled file [format]]\n" % __file__
-            )
+            sys.stderr.write(f"usage: {__file__} [-|CPython compiled file [format]]\n")
             sys.exit(2)
     elif argc == 3:
         fn, asm_format = sys.argv[1:3]
diff --git a/xdis/instruction.py b/xdis/instruction.py
index dc355e5a..34ea3331 100644
--- a/xdis/instruction.py
+++ b/xdis/instruction.py
@@ -170,7 +170,7 @@ class Instruction(NamedTuple):
     argval: Any
 
     # String representation of argval if argval is not None.
-    argrepr: str
+    argrepr: Optional[str]
 
     # Offset of the instruction
     offset: int
@@ -293,7 +293,7 @@ def disassemble(
                     hex_bytecode += " %02x" % (self.arg % 256)
                 else:
                     hex_bytecode += " 00"
-            elif self.inst_size == 3:
+            elif self.inst_size == 3 and self.arg is not None:
                 # Not 3.6 or later
                 hex_bytecode += " %02x %02x" % divmod(self.arg, 256)
 
@@ -310,7 +310,7 @@ def disassemble(
             # for "asm" format, want additional explicit information
             # linking operands to tables.
             if asm_format == "asm":
-                if self.is_jump():
+                if self.is_jump() and self.argrepr is not None:
                     assert self.argrepr.startswith("to ")
                     jump_target = self.argrepr[len("to ") :]
                     fields.append("L" + jump_target)
@@ -318,7 +318,11 @@ def disassemble(
                     fields.append(repr(self.arg))
                     fields.append("(%s)" % argrepr)
                     argrepr = None
-                elif self.optype == "const" and not re.search(r"\s", argrepr):
+                elif (
+                    self.optype == "const"
+                    and argrepr is not None
+                    and not re.search(r"\s", argrepr)
+                ):
                     fields.append(repr(self.arg))
                     fields.append("(%s)" % argrepr)
                     argrepr = None
@@ -326,7 +330,11 @@ def disassemble(
                     fields.append(repr(self.arg))
             elif asm_format in ("extended", "extended-bytes"):
                 op = self.opcode
-                if self.is_jump() and line_starts.get(self.argval) is not None:
+                if (
+                    self.is_jump()
+                    and line_starts is not None
+                    and line_starts.get(self.argval) is not None
+                ):
                     new_instruction = list(self)
                     new_instruction[-2] = f"To line {line_starts[self.argval]}"
                     self = Instruction(*new_instruction)
@@ -381,7 +389,7 @@ def disassemble(
                             prefix += "TOS = "
                         fields.append(f"{prefix}{self.tos_str}")
                     pass
-                else:
+                elif self.argrepr is not None:
                     fields.append(self.argrepr)
                 pass
             pass
@@ -408,7 +416,7 @@ def disassemble(
                 pass
             elif (
                 hasattr(opc, "opcode_arg_fmt") and opc.opname[op] in opc.opcode_arg_fmt
-            ):
+            ) and self.argrepr is not None:
                 fields.append(self.argrepr)
                 pass
             pass
diff --git a/xdis/op_imports.py b/xdis/op_imports.py
index b7fc8439..37e412d5 100644
--- a/xdis/op_imports.py
+++ b/xdis/op_imports.py
@@ -204,7 +204,7 @@ def get_opcode_module(version_info=None, variant=None):
                 pass
         except ImportError:
             # Python may be too old, e.g. < 2.6 or implementation may
-            # just not have platform
+            # just not have the ``platform`` attribute.
             pass
     elif variant != "Graal":
         vers_str += variant
diff --git a/xdis/opcodes/format/extended.py b/xdis/opcodes/format/extended.py
index 78640c6a..3063e004 100644
--- a/xdis/opcodes/format/extended.py
+++ b/xdis/opcodes/format/extended.py
@@ -663,7 +663,7 @@ def extended_format_CALL_METHOD(opc, instructions) -> Tuple[str, Optional[int]]:
 
 def extended_format_RAISE_VARARGS_older(
     opc, instructions: List[Instruction]
-) -> Tuple[Optional[str], int]:
+) -> Tuple[str, Optional[int]]:
     raise_inst = instructions[0]
     assert raise_inst.opname == "RAISE_VARARGS"
     argc = raise_inst.argval