diff --git a/lib/python/pyflyby/_interactive.py b/lib/python/pyflyby/_interactive.py
index 9013fcda..b0c450cc 100644
--- a/lib/python/pyflyby/_interactive.py
+++ b/lib/python/pyflyby/_interactive.py
@@ -15,7 +15,7 @@
 import subprocess
 import sys
 
-from typing import List, Any, Dict
+from typing import List, Any, Dict, Union, Literal
 
 
 from   pyflyby._autoimp         import (LoadSymbolError, ScopeStack, auto_eval,
@@ -2269,7 +2269,9 @@ def disable(self):
 
     def _safe_call(self, function, *args, **kwargs):
         on_error = kwargs.pop("on_error", None)
-        raise_on_error = kwargs.pop("raise_on_error", "if_debug")
+        raise_on_error: Union[bool, Literal["if_debug"]] = kwargs.pop(
+            "raise_on_error", "if_debug"
+        )
         if self._errored:
             # If we previously errored, then we should already have
             # unregistered the hook that led to here.  However, in some corner
@@ -2295,7 +2297,7 @@ def _safe_call(self, function, *args, **kwargs):
                     logger.error("Error trying to disable: %s: %s",
                                  type(e2).__name__, e2)
                 # Raise or print traceback in debug mode.
-                if raise_on_error == True:
+                if raise_on_error is True:
                     raise
                 elif raise_on_error == 'if_debug':
                     if logger.debug_enabled:
@@ -2305,7 +2307,7 @@ def _safe_call(self, function, *args, **kwargs):
                             import traceback
                             traceback.print_exc()
                         raise
-                elif raise_on_error == False:
+                elif raise_on_error is False:
                     if logger.debug_enabled:
                         import traceback
                         traceback.print_exc()
@@ -2328,8 +2330,13 @@ def reset_state_new_cell(self):
                          sorted([k for k,v in autoimported.items() if not v]))
         self._autoimported_this_cell = {}
 
-    def auto_import(self, arg, namespaces=None,
-                    raise_on_error='if_debug', on_error=None):
+    def auto_import(
+        self,
+        arg,
+        namespaces=None,
+        raise_on_error: Union[bool, Literal["if_debug"]] = "if_debug",
+        on_error=None,
+    ):
         if namespaces is None:
             namespaces = get_global_namespaces(self._ip)
 
diff --git a/lib/python/pyflyby/_parse.py b/lib/python/pyflyby/_parse.py
index a566f11a..140bb4c1 100644
--- a/lib/python/pyflyby/_parse.py
+++ b/lib/python/pyflyby/_parse.py
@@ -20,7 +20,7 @@
 import sys
 from   textwrap                 import dedent
 import types
-from   typing                   import Any, List, Optional, Tuple, Union, cast
+from   typing                   import Any, List, Optional, Tuple, Union, cast, Literal
 import warnings
 
 
@@ -353,7 +353,7 @@ def _annotate_ast_nodes(ast_node: ast.AST) -> AnnotatedAst:
 
 
 def _annotate_ast_startpos(
-    ast_node: ast.AST, parent_ast_node, minpos, text, flags
+    ast_node: ast.AST, parent_ast_node, minpos: FilePos, text: FileText, flags
 ) -> bool:
     r"""
     Annotate ``ast_node``.  Set ``ast_node.startpos`` to the starting position
@@ -410,8 +410,8 @@ def _annotate_ast_startpos(
     # Walk all nodes/fields of the AST.  We implement this as a custom
     # depth-first search instead of using ast.walk() or ast.NodeVisitor
     # so that we can easily keep track of the preceding node's lineno.
-    child_minpos = minpos
-    is_first_child = True
+    child_minpos: FilePos = minpos
+    is_first_child: bool = True
     leftstr_node = None
     for child_node in _iter_child_nodes_in_order(aast_node):
         leftstr = _annotate_ast_startpos(
@@ -677,7 +677,7 @@ def _ast_node_is_in_docstring_position(ast_node):
     return False
 
 
-def infer_compile_mode(arg):
+def infer_compile_mode(arg:ast.AST) -> Literal['exec','eval','single']:
     """
     Infer the mode needed to compile ``arg``.
 
@@ -688,19 +688,18 @@ def infer_compile_mode(arg):
     """
     # Infer mode from ast object.
     if isinstance(arg, ast.Module):
-        mode = "exec"
+        return "exec"
     elif isinstance(arg, ast.Expression):
-        mode = "eval"
+        return "eval"
     elif isinstance(arg, ast.Interactive):
-        mode = "single"
+        return "single"
     else:
         raise TypeError(
             "Expected Module/Expression/Interactive ast node; got %s"
             % (type(arg).__name__))
-    return mode
 
 
-class _DummyAst_Node(object):
+class _DummyAst_Node:
     pass
 
 
@@ -954,8 +953,9 @@ def from_filename(cls, filename):
         return cls.from_text(Filename(filename))
 
     @classmethod
-    def from_text(cls, text, filename=None, startpos=None, flags=None,
-                  auto_flags=False):
+    def from_text(
+        cls, text, filename=None, startpos=None, flags=None, auto_flags: bool = False
+    ):
         """
         :type text:
           `FileText` or convertible
@@ -1153,7 +1153,7 @@ def expression_ast_node(self) -> Optional[ast.Expression]:
         else:
             return None
 
-    def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
+    def parse(self, mode: Optional[str] = None) -> Union[ast.Expression, ast.Module]:
         """
         Parse the source text into an AST.
 
@@ -1174,7 +1174,7 @@ def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
                 return self.expression_ast_node
             else:
                 raise SyntaxError
-        elif mode == None:
+        elif mode is None:
             if self.expression_ast_node:
                 return self.expression_ast_node
             else:
@@ -1185,7 +1185,7 @@ def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
         else:
             raise ValueError("parse(): invalid mode=%r" % (mode,))
 
-    def compile(self, mode=None):
+    def compile(self, mode: Optional[str] = None):
         """
         Parse into AST and compile AST into code.
 
@@ -1193,9 +1193,9 @@ def compile(self, mode=None):
           ``CodeType``
         """
         ast_node = self.parse(mode=mode)
-        mode = infer_compile_mode(ast_node)
+        c_mode = infer_compile_mode(ast_node)
         filename = str(self.filename or "<unknown>")
-        return compile(ast_node, filename, mode)
+        return compile(ast_node, filename, c_mode)
 
     @cached_property
     def statements(self) -> Tuple[PythonStatement, ...]:
diff --git a/lib/python/pyflyby/_py.py b/lib/python/pyflyby/_py.py
index 3da73932..e39541c5 100644
--- a/lib/python/pyflyby/_py.py
+++ b/lib/python/pyflyby/_py.py
@@ -286,19 +286,6 @@
 from   pyflyby._util            import cmp
 from   shlex                    import quote as shquote
 
-usage = """
-py --- command-line python multitool with automatic importing
-
-$ py [--file]   filename.py arg1 arg2      Execute file
-$ py [--apply]  function arg1 arg2         Call function
-$ py [--eval]  'function(arg1, arg2)'      Evaluate code
-$ py [--module] modname arg1 arg2          Run a module
-
-$ py --debug    file/code... args...       Debug code
-$ py --debug    PID                        Attach debugger to PID
-
-$ py                                       IPython shell
-""".strip()
 
 # TODO: add --tidy-imports, etc
 
@@ -377,6 +364,19 @@
 from   pyflyby._parse           import PythonBlock
 from   pyflyby._util            import indent, prefixes
 
+usage = """
+py --- command-line python multitool with automatic importing
+
+$ py [--file]   filename.py arg1 arg2      Execute file
+$ py [--apply]  function arg1 arg2         Call function
+$ py [--eval]  'function(arg1, arg2)'      Evaluate code
+$ py [--module] modname arg1 arg2          Run a module
+
+$ py --debug    file/code... args...       Debug code
+$ py --debug    PID                        Attach debugger to PID
+
+$ py                                       IPython shell
+""".strip()
 
 # Default compiler flags (feature flags) used for all user code.  We include
 # "print_function" here, but we also use auto_flags=True, which means
@@ -409,7 +409,7 @@ def _get_argspec(arg:Any) -> inspect.FullArgSpec:
         "_get_argspec: unexpected %s" % (type(arg).__name__,))
 
 
-def _requires_parens_as_function(function_name:str):
+def _requires_parens_as_function(function_name:str) -> bool:
     """
     Returns whether the given string of a callable would require parentheses
     around it to call it.
@@ -552,7 +552,7 @@ class _ParseInterruptedWantSource(Exception):
     pass
 
 
-class UserExpr(object):
+class UserExpr:
     """
     An expression from user input, and its evaluated value.
 
@@ -647,7 +647,7 @@ def __init__(self, arg, namespace, arg_mode, source=None):
         else:
             raise ValueError("UserExpr(): bad arg_mode=%r" % (arg_mode,))
 
-    def _infer_and_evaluate(self):
+    def _infer_and_evaluate(self) -> None:
         if self._original_arg_mode == "raw_value":
             pass
         elif self._original_arg_mode == "eval":
@@ -891,7 +891,7 @@ class NotAFunctionError(Exception):
     pass
 
 
-def _get_help(expr, verbosity=1):
+def _get_help(expr:UserExpr, verbosity:int=1) -> str:
     """
     Construct a help string.
 
@@ -1053,7 +1053,7 @@ def auto_apply(function, commandline_args, namespace, arg_mode=None,
 
 
 @total_ordering
-class LoggedList(object):
+class LoggedList:
     """
     List that logs which members have not yet been accessed (nor removed).
     """
diff --git a/lib/python/pyflyby/_util.py b/lib/python/pyflyby/_util.py
index d271dded..c525246c 100644
--- a/lib/python/pyflyby/_util.py
+++ b/lib/python/pyflyby/_util.py
@@ -4,7 +4,7 @@
 
 
 
-from   contextlib               import contextmanager
+from   contextlib               import contextmanager, ExitStack
 import inspect
 import os
 import sys
@@ -451,7 +451,6 @@ def cmp(a, b):
 
 
 # Create a context manager with an arbitrary number of contexts.
-from contextlib import ExitStack
 @contextmanager
 def nested(*mgrs):
     with ExitStack() as stack: