diff --git a/kittens/ask/main.py b/kittens/ask/main.py
index 13206edf6..5133d7b30 100644
--- a/kittens/ask/main.py
+++ b/kittens/ask/main.py
@@ -4,15 +4,19 @@
 
 import os
 from contextlib import suppress
+from typing import TYPE_CHECKING, Dict, List, Union
 
 from kitty.cli import parse_args
-from kitty.constants import cache_dir
 from kitty.cli_stub import AskCLIOptions
+from kitty.constants import cache_dir
 
-from ..tui.operations import alternate_screen, styled
 from ..tui.handler import result_handler
+from ..tui.operations import alternate_screen, styled
 
-readline = None
+if TYPE_CHECKING:
+    import readline
+else:
+    readline = None
 
 
 def get_history_items():
@@ -98,7 +102,7 @@ def main(args):
         raise SystemExit(e.code)
 
     init_readline(readline)
-    ans = {'items': items}
+    response = None
 
     with alternate_screen(), HistoryCompleter(args.name):
         if args.message:
@@ -106,7 +110,11 @@ def main(args):
 
         prompt = '> '
         with suppress(KeyboardInterrupt, EOFError):
-            ans['response'] = input(prompt)
+            response = input(prompt)
+    if response is None:
+        ans: Dict[str, Union[str, List[str]]] = {'items': items}
+    else:
+        ans = {'items': items, 'response': response}
     return ans
 
 
diff --git a/kittens/diff/__init__.py b/kittens/diff/__init__.py
index e69de29bb..c325117e7 100644
--- a/kittens/diff/__init__.py
+++ b/kittens/diff/__init__.py
@@ -0,0 +1,8 @@
+class GlobalData:
+
+    def __init__(self):
+        self.title = ''
+        self.cmd = ''
+
+
+global_data = GlobalData
diff --git a/kittens/diff/collect.py b/kittens/diff/collect.py
index 1f9808043..e51fecd90 100644
--- a/kittens/diff/collect.py
+++ b/kittens/diff/collect.py
@@ -8,7 +8,7 @@ from contextlib import suppress
 from functools import lru_cache
 from hashlib import md5
 from mimetypes import guess_type
-from typing import Dict
+from typing import Dict, List, Set
 
 path_name_map: Dict[str, str] = {}
 
@@ -20,11 +20,12 @@ class Segment:
     def __init__(self, start, start_code):
         self.start = start
         self.start_code = start_code
+        self.end = None
+        self.end_code = None
 
     def __repr__(self):
         return 'Segment(start={!r}, start_code={!r}, end={!r}, end_code={!r})'.format(
-                self.start, self.start_code, getattr(self, 'end', None), getattr(self, 'end_code', None)
-        )
+            self.start, self.start_code, self.end, self.end_code)
 
 
 class Collection:
@@ -81,8 +82,10 @@ class Collection:
 
 
 def collect_files(collection, left, right):
-    left_names, right_names = set(), set()
-    left_path_map, right_path_map = {}, {}
+    left_names: Set[str] = set()
+    right_names: Set[str] = set()
+    left_path_map: Dict[str, str] = {}
+    right_path_map: Dict[str, str] = {}
 
     def walk(base, names, pmap):
         for dirpath, dirnames, filenames in os.walk(base):
@@ -178,7 +181,7 @@ def create_collection(left, right):
     return collection
 
 
-highlight_data = {}
+highlight_data: Dict[str, List] = {}
 
 
 def set_highlight_data(data):
diff --git a/kittens/diff/config.py b/kittens/diff/config.py
index 0329ed8d6..1295fe405 100644
--- a/kittens/diff/config.py
+++ b/kittens/diff/config.py
@@ -3,18 +3,20 @@
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 
 import os
+from typing import Any, Dict, Optional, Type
 
-from kitty.conf.utils import (
-    init_config as _init_config, key_func, load_config as _load_config, merge_dicts,
-    parse_config_base, parse_kittens_key, resolve_config
-)
 from kitty.conf.definition import config_lines
+from kitty.conf.utils import (
+    init_config as _init_config, key_func, load_config as _load_config,
+    merge_dicts, parse_config_base, parse_kittens_key, resolve_config
+)
 from kitty.constants import config_dir
+from kitty.options_stub import DiffOptions
 from kitty.rgb import color_as_sgr
 
-from .config_data import type_convert, all_options
+from .config_data import all_options, type_convert
 
-defaults = None
+defaults: Optional[DiffOptions] = None
 
 formats = {
     'title': '',
@@ -79,13 +81,15 @@ def parse_start_search(func, rest):
 
 def special_handling(key, val, ans):
     if key == 'map':
-        action, *key_def = parse_kittens_key(val, args_funcs)
-        ans['key_definitions'][tuple(key_def)] = action
-        return True
+        x = parse_kittens_key(val, args_funcs)
+        if x is not None:
+            action, *key_def = x
+            ans['key_definitions'][tuple(key_def)] = action
+            return True
 
 
 def parse_config(lines, check_keys=True):
-    ans = {'key_definitions': {}}
+    ans: Dict[str, Any] = {'key_definitions': {}}
     parse_config_base(
         lines,
         defaults,
@@ -112,7 +116,9 @@ def parse_defaults(lines, check_keys=False):
     return parse_config(lines, check_keys)
 
 
-Options, defaults = _init_config(config_lines(all_options), parse_defaults)
+x = _init_config(config_lines(all_options), parse_defaults)
+Options: Type[DiffOptions] = x[0]
+defaults = x[1]
 
 
 def load_config(*paths, overrides=None):
diff --git a/kittens/diff/highlight.py b/kittens/diff/highlight.py
index 0de0e9b1a..52a07a1cf 100644
--- a/kittens/diff/highlight.py
+++ b/kittens/diff/highlight.py
@@ -5,6 +5,7 @@
 import concurrent
 import os
 import re
+from typing import List, Optional
 
 from pygments import highlight  # type: ignore
 from pygments.formatter import Formatter  # type: ignore
@@ -35,11 +36,15 @@ class DiffFormatter(Formatter):
         for token, style in self.style:
             start = []
             end = []
+            fstart = fend = ''
             # a style item is a tuple in the following form:
             # colors are readily specified in hex: 'RRGGBB'
-            if style['color']:
-                start.append('38' + color_as_sgr(parse_sharp(style['color'])))
-                end.append('39')
+            col = style['color']
+            if col:
+                pc = parse_sharp(col)
+                if pc is not None:
+                    start.append('38' + color_as_sgr(pc))
+                    end.append('39')
             if style['bold']:
                 start.append('1')
                 end.append('22')
@@ -50,9 +55,9 @@ class DiffFormatter(Formatter):
                 start.append('4')
                 end.append('24')
             if start:
-                start = '\033[{}m'.format(';'.join(start))
-                end = '\033[{}m'.format(';'.join(end))
-            self.styles[token] = start or '', end or ''
+                fstart = '\033[{}m'.format(';'.join(start))
+                fend = '\033[{}m'.format(';'.join(end))
+            self.styles[token] = fstart, fend
 
     def format(self, tokensource, outfile):
         for ttype, value in tokensource:
@@ -76,7 +81,7 @@ class DiffFormatter(Formatter):
                 outfile.write(value)
 
 
-formatter = None
+formatter: Optional[DiffFormatter] = None
 
 
 def initialize_highlighter(style='default'):
@@ -102,8 +107,8 @@ split_pat = re.compile(r'(\033\[.*?m)')
 
 
 def highlight_line(line):
-    ans = []
-    current = None
+    ans: List[Segment] = []
+    current: Optional[Segment] = None
     pos = 0
     for x in split_pat.split(line):
         if x.startswith('\033'):
@@ -133,7 +138,6 @@ def highlight_collection(collection, aliases=None):
     jobs = {}
     ans = {}
     with concurrent.futures.ProcessPoolExecutor(max_workers=os.cpu_count()) as executor:
-        highlight_collection.processes = executor._processes
         for path, item_type, other_path in collection:
             if item_type != 'rename':
                 for p in (path, other_path):
@@ -156,8 +160,9 @@ def main():
     # kitty +runpy "from kittens.diff.highlight import main; main()" file
     import sys
     initialize_highlighter()
-    with open(sys.argv[-1]) as f:
-        highlighted = highlight_data(f.read(), f.name, defaults.syntax_aliases)
-    if highlighted is None:
-        raise SystemExit('Unknown filetype: {}'.format(sys.argv[-1]))
-    print(highlighted)
+    if defaults is not None:
+        with open(sys.argv[-1]) as f:
+            highlighted = highlight_data(f.read(), f.name, defaults.syntax_aliases)
+        if highlighted is None:
+            raise SystemExit('Unknown filetype: {}'.format(sys.argv[-1]))
+        print(highlighted)
diff --git a/kittens/diff/main.py b/kittens/diff/main.py
index 6f0e741ca..2a49be1c9 100644
--- a/kittens/diff/main.py
+++ b/kittens/diff/main.py
@@ -13,6 +13,7 @@ from collections import defaultdict
 from contextlib import suppress
 from functools import partial
 from gettext import gettext as _
+from typing import DefaultDict, List, Tuple
 
 from kitty.cli import CONFIG_HELP, parse_args
 from kitty.cli_stub import DiffCLIOptions
@@ -24,9 +25,10 @@ from .collect import (
     create_collection, data_for_path, lines_for_path, sanitize,
     set_highlight_data
 )
+from . import global_data
 from .config import init_config
 from .patch import Differ, set_diff_command, worker_processes
-from .render import ImageSupportWarning, LineRef, render_diff
+from .render import ImageSupportWarning, LineRef, Reference, render_diff
 from .search import BadRegex, Search
 from ..tui.handler import Handler
 from ..tui.images import ImageManager
@@ -186,7 +188,7 @@ class DiffHandler(Handler):
     def render_diff(self):
         self.diff_lines = tuple(render_diff(self.collection, self.diff_map, self.args, self.screen_size.cols, self.image_manager))
         self.margin_size = render_diff.margin_size
-        self.ref_path_map = defaultdict(list)
+        self.ref_path_map: DefaultDict[str, List[Tuple[int, Reference]]] = defaultdict(list)
         for i, l in enumerate(self.diff_lines):
             self.ref_path_map[l.ref.path].append((i, l.ref))
         self.max_scroll_pos = len(self.diff_lines) - self.num_lines
@@ -271,7 +273,7 @@ class DiffHandler(Handler):
 
     def init_terminal_state(self):
         self.cmd.set_line_wrapping(False)
-        self.cmd.set_window_title(main.title)
+        self.cmd.set_window_title(global_data.title)
         self.cmd.set_default_colors(
             fg=self.opts.foreground, bg=self.opts.background,
             cursor=self.opts.foreground, select_fg=self.opts.select_fg,
@@ -547,7 +549,7 @@ def main(args):
     if len(items) != 2:
         raise SystemExit('You must specify exactly two files/directories to compare')
     left, right = items
-    main.title = _('{} vs. {}').format(left, right)
+    global_data.title = _('{} vs. {}').format(left, right)
     if os.path.isdir(left) != os.path.isdir(right):
         raise SystemExit('The items to be diffed should both be either directories or files. Comparing a directory to a file is not valid.')
     opts = init_config(args)
diff --git a/kittens/diff/patch.py b/kittens/diff/patch.py
index 358e18fd7..1c9d3421a 100644
--- a/kittens/diff/patch.py
+++ b/kittens/diff/patch.py
@@ -7,14 +7,17 @@ import os
 import shlex
 import shutil
 import subprocess
+from typing import List, Optional, Tuple
 
+from . import global_data
 from .collect import lines_for_path
 from .diff_speedup import changed_center
 
-left_lines = right_lines = None
+left_lines: Tuple[str, ...] = ()
+right_lines: Tuple[str, ...] = ()
 GIT_DIFF = 'git diff --no-color --no-ext-diff --exit-code -U_CONTEXT_ --no-index --'
 DIFF_DIFF = 'diff -p -U _CONTEXT_ --'
-worker_processes = []
+worker_processes: List[int] = []
 
 
 def find_differ():
@@ -31,16 +34,17 @@ def set_diff_command(opt):
             raise SystemExit('Failed to find either the git or diff programs on your system')
     else:
         cmd = opt
-    set_diff_command.cmd = cmd
+    global_data.cmd = cmd
 
 
-def run_diff(file1, file2, context=3):
+def run_diff(file1: str, file2: str, context: int = 3):
     # returns: ok, is_different, patch
-    cmd = shlex.split(set_diff_command.cmd.replace('_CONTEXT_', str(context)))
+    cmd = shlex.split(global_data.cmd.replace('_CONTEXT_', str(context)))
     # we resolve symlinks because git diff does not follow symlinks, while diff
     # does. We want consistent behavior, also for integration with git difftool
     # we always want symlinks to be followed.
-    path1, path2 = map(os.path.realpath, (file1, file2))
+    path1 = os.path.realpath(file1)
+    path2 = os.path.realpath(file2)
     p = subprocess.Popen(
             cmd + [path1, path2],
             stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.DEVNULL)
@@ -96,7 +100,7 @@ class Hunk:
         self.title = title
         self.added_count = self.removed_count = 0
         self.chunks = []
-        self.current_chunk = None
+        self.current_chunk: Optional[Chunk] = None
         self.largest_line_number = max(self.left_start + self.left_count, self.right_start + self.right_count)
 
     def new_chunk(self, is_context=False):
@@ -125,20 +129,24 @@ class Hunk:
 
     def add_line(self):
         self.ensure_diff_chunk()
-        self.current_chunk.add_line()
+        if self.current_chunk is not None:
+            self.current_chunk.add_line()
         self.added_count += 1
 
     def remove_line(self):
         self.ensure_diff_chunk()
-        self.current_chunk.remove_line()
+        if self.current_chunk is not None:
+            self.current_chunk.remove_line()
         self.removed_count += 1
 
     def context_line(self):
         self.ensure_context_chunk()
-        self.current_chunk.context_line()
+        if self.current_chunk is not None:
+            self.current_chunk.context_line()
 
     def finalize(self):
-        self.chunks.append(self.current_chunk)
+        if self.current_chunk is not None:
+            self.chunks.append(self.current_chunk)
         del self.current_chunk
         # Sanity check
         c = self.chunks[-1]
@@ -158,7 +166,7 @@ def parse_range(x):
 
 
 def parse_hunk_header(line):
-    parts = tuple(filter(None, line.split('@@', 2)))
+    parts: Tuple[str, ...] = tuple(filter(None, line.split('@@', 2)))
     linespec = parts[0].strip()
     title = ''
     if len(parts) == 2:
@@ -208,7 +216,7 @@ def parse_patch(raw):
 
 class Differ:
 
-    diff_executor = None
+    diff_executor: Optional[concurrent.futures.ThreadPoolExecutor] = None
 
     def __init__(self):
         self.jmap = {}
@@ -223,7 +231,8 @@ class Differ:
     def __call__(self, context=3):
         global left_lines, right_lines
         ans = {}
-        executor = Differ.diff_executor
+        executor = self.diff_executor
+        assert executor is not None
         jobs = {executor.submit(run_diff, key, self.jmap[key], context): key for key in self.jobs}
         for future in concurrent.futures.as_completed(jobs):
             key = jobs[future]
diff --git a/kittens/diff/render.py b/kittens/diff/render.py
index 3f0db8512..b3cea34f1 100644
--- a/kittens/diff/render.py
+++ b/kittens/diff/render.py
@@ -3,31 +3,32 @@
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 
 import warnings
+from functools import lru_cache
 from gettext import gettext as _
 from itertools import repeat, zip_longest
 from math import ceil
+from typing import Callable, Iterable, List, Optional
 
 from kitty.fast_data_types import truncate_point_for_length, wcswidth
 
-from ..tui.images import can_display_images
 from .collect import (
     Segment, data_for_path, highlights_for_path, is_image, lines_for_path,
     path_name_map, sanitize
 )
 from .config import formats
 from .diff_speedup import split_with_highlights as _split_with_highlights
+from ..tui.images import can_display_images
 
 
 class ImageSupportWarning(Warning):
     pass
 
 
+@lru_cache(maxsize=2)
 def images_supported():
-    ans = getattr(images_supported, 'ans', None)
-    if ans is None:
-        images_supported.ans = ans = can_display_images()
-        if not ans:
-            warnings.warn('ImageMagick not found images cannot be displayed', ImageSupportWarning)
+    ans = can_display_images()
+    if not ans:
+        warnings.warn('ImageMagick not found images cannot be displayed', ImageSupportWarning)
     return ans
 
 
@@ -44,6 +45,8 @@ class Ref:
 class LineRef(Ref):
 
     __slots__ = ('src_line_number', 'wrapped_line_idx')
+    src_line_number: int
+    wrapped_line_idx: int
 
     def __init__(self, sln, wli=0):
         object.__setattr__(self, 'src_line_number', sln)
@@ -53,6 +56,8 @@ class LineRef(Ref):
 class Reference(Ref):
 
     __slots__ = ('path', 'extra')
+    path: str
+    extra: Optional[LineRef]
 
     def __init__(self, path, extra=None):
         object.__setattr__(self, 'path', path)
@@ -111,8 +116,8 @@ def place_in(text, sz):
     return fill_in(fit_in(text, sz), sz)
 
 
-def format_func(which):
-    def formatted(text):
+def format_func(which: str) -> Callable[[str], str]:
+    def formatted(text: str) -> str:
         fmt = formats[which]
         return '\x1b[' + fmt + 'm' + text + '\x1b[0m'
     formatted.__name__ = which + '_format'
@@ -226,7 +231,7 @@ class DiffData:
         return []
 
 
-def render_diff_line(number, text, ltype, margin_size, available_cols):
+def render_diff_line(number, text, ltype, margin_size, available_cols) -> str:
     margin = margin_bg_map[ltype](place_in(number, margin_size))
     content = text_bg_map[ltype](fill_in(text or '', available_cols))
     return margin + content
@@ -292,7 +297,8 @@ def lines_for_chunk(data, hunk_num, chunk, chunk_num):
     else:
         common = min(chunk.left_count, chunk.right_count)
         for i in range(max(chunk.left_count, chunk.right_count)):
-            ll, rl = [], []
+            ll: List[str] = []
+            rl: List[str] = []
             if i < chunk.left_count:
                 rln = ref_ln = chunk.left_start + i
                 ll.extend(render_half_line(
@@ -416,7 +422,8 @@ def render_image(path, is_left, available_cols, margin_size, image_manager):
 
 def image_lines(left_path, right_path, columns, margin_size, image_manager):
     available_cols = columns // 2 - margin_size
-    left_lines, right_lines = iter(()), iter(())
+    left_lines: Iterable[str] = iter(())
+    right_lines: Iterable[str] = iter(())
     if left_path is not None:
         left_lines = render_image(left_path, True, available_cols, margin_size, image_manager)
     if right_path is not None:
@@ -439,52 +446,59 @@ def image_lines(left_path, right_path, columns, margin_size, image_manager):
         is_change_start = False
 
 
-def render_diff(collection, diff_map, args, columns, image_manager):
-    largest_line_number = 0
-    for path, item_type, other_path in collection:
-        if item_type == 'diff':
-            patch = diff_map.get(path)
-            if patch is not None:
-                largest_line_number = max(largest_line_number, patch.largest_line_number)
+class RenderDiff:
 
-    margin_size = render_diff.margin_size = max(3, len(str(largest_line_number)) + 1)
-    last_item_num = len(collection) - 1
+    margin_size: int = 0
 
-    for i, (path, item_type, other_path) in enumerate(collection):
-        item_ref = Reference(path)
-        is_binary = isinstance(data_for_path(path), bytes)
-        if not is_binary and item_type == 'diff' and isinstance(data_for_path(other_path), bytes):
-            is_binary = True
-        is_img = is_binary and (is_image(path) or is_image(other_path)) and images_supported()
-        yield from yield_lines_from(title_lines(path, other_path, args, columns, margin_size), item_ref, False)
-        if item_type == 'diff':
-            if is_binary:
-                if is_img:
-                    ans = image_lines(path, other_path, columns, margin_size, image_manager)
+    def __call__(self, collection, diff_map, args, columns, image_manager):
+        largest_line_number = 0
+        for path, item_type, other_path in collection:
+            if item_type == 'diff':
+                patch = diff_map.get(path)
+                if patch is not None:
+                    largest_line_number = max(largest_line_number, patch.largest_line_number)
+
+        margin_size = self.margin_size = max(3, len(str(largest_line_number)) + 1)
+        last_item_num = len(collection) - 1
+
+        for i, (path, item_type, other_path) in enumerate(collection):
+            item_ref = Reference(path)
+            is_binary = isinstance(data_for_path(path), bytes)
+            if not is_binary and item_type == 'diff' and isinstance(data_for_path(other_path), bytes):
+                is_binary = True
+            is_img = is_binary and (is_image(path) or is_image(other_path)) and images_supported()
+            yield from yield_lines_from(title_lines(path, other_path, args, columns, margin_size), item_ref, False)
+            if item_type == 'diff':
+                if is_binary:
+                    if is_img:
+                        ans = image_lines(path, other_path, columns, margin_size, image_manager)
+                    else:
+                        ans = yield_lines_from(binary_lines(path, other_path, columns, margin_size), item_ref)
                 else:
-                    ans = yield_lines_from(binary_lines(path, other_path, columns, margin_size), item_ref)
-            else:
-                ans = lines_for_diff(path, other_path, diff_map[path], args, columns, margin_size)
-        elif item_type == 'add':
-            if is_binary:
-                if is_img:
-                    ans = image_lines(None, path, columns, margin_size, image_manager)
+                    ans = lines_for_diff(path, other_path, diff_map[path], args, columns, margin_size)
+            elif item_type == 'add':
+                if is_binary:
+                    if is_img:
+                        ans = image_lines(None, path, columns, margin_size, image_manager)
+                    else:
+                        ans = yield_lines_from(binary_lines(None, path, columns, margin_size), item_ref)
                 else:
-                    ans = yield_lines_from(binary_lines(None, path, columns, margin_size), item_ref)
-            else:
-                ans = all_lines(path, args, columns, margin_size, is_add=True)
-        elif item_type == 'removal':
-            if is_binary:
-                if is_img:
-                    ans = image_lines(path, None, columns, margin_size, image_manager)
+                    ans = all_lines(path, args, columns, margin_size, is_add=True)
+            elif item_type == 'removal':
+                if is_binary:
+                    if is_img:
+                        ans = image_lines(path, None, columns, margin_size, image_manager)
+                    else:
+                        ans = yield_lines_from(binary_lines(path, None, columns, margin_size), item_ref)
                 else:
-                    ans = yield_lines_from(binary_lines(path, None, columns, margin_size), item_ref)
+                    ans = all_lines(path, args, columns, margin_size, is_add=False)
+            elif item_type == 'rename':
+                ans = yield_lines_from(rename_lines(path, other_path, args, columns, margin_size), item_ref)
             else:
-                ans = all_lines(path, args, columns, margin_size, is_add=False)
-        elif item_type == 'rename':
-            ans = yield_lines_from(rename_lines(path, other_path, args, columns, margin_size), item_ref)
-        else:
-            raise ValueError('Unsupported item type: {}'.format(item_type))
-        yield from ans
-        if i < last_item_num:
-            yield Line('', item_ref)
+                raise ValueError('Unsupported item type: {}'.format(item_type))
+            yield from ans
+            if i < last_item_num:
+                yield Line('', item_ref)
+
+
+render_diff = RenderDiff()
diff --git a/kittens/hints/main.py b/kittens/hints/main.py
index f09472ca6..a9b77d1d3 100644
--- a/kittens/hints/main.py
+++ b/kittens/hints/main.py
@@ -9,11 +9,12 @@ import sys
 from functools import lru_cache
 from gettext import gettext as _
 from itertools import repeat
+from typing import Callable, Dict, List, Optional, Tuple
 
 from kitty.cli import parse_args
 from kitty.cli_stub import HintsCLIOptions
 from kitty.fast_data_types import set_clipboard_string
-from kitty.key_encoding import key_defs as K, backspace_key, enter_key
+from kitty.key_encoding import backspace_key, enter_key, key_defs as K
 from kitty.utils import screen_size_function
 
 from ..tui.handler import Handler, result_handler
@@ -199,7 +200,7 @@ def regex_finditer(pat, minimum_match_length, text):
 
 closing_bracket_map = {'(': ')', '[': ']', '{': '}', '<': '>', '*': '*', '"': '"', "'": "'"}
 opening_brackets = ''.join(closing_bracket_map)
-postprocessor_map = {}
+postprocessor_map: Dict[str, Callable[[str, int, int], Tuple[int, int]]] = {}
 
 
 def postprocessor(func):
@@ -304,8 +305,8 @@ def functions_for(args):
     return pattern, post_processors
 
 
-def convert_text(text, cols):
-    lines = []
+def convert_text(text: str, cols: int) -> str:
+    lines: List[str] = []
     empty_line = '\0' * cols
     for full_line in text.split('\n'):
         if full_line:
@@ -574,10 +575,11 @@ def handle_result(args, data, target_window_id, boss):
     matches, groupdicts = [], []
     for m, g in zip(data['match'], data['groupdicts']):
         if m:
-            matches.append(m), groupdicts.append(g)
+            matches.append(m)
+            groupdicts.append(g)
     joiner = data['multiple_joiner']
     try:
-        is_int = int(joiner)
+        is_int: Optional[int] = int(joiner)
     except Exception:
         is_int = None
     text_type = data['type']
diff --git a/kittens/icat/main.py b/kittens/icat/main.py
index aaefe3eed..4d569a004 100755
--- a/kittens/icat/main.py
+++ b/kittens/icat/main.py
@@ -9,14 +9,17 @@ import signal
 import sys
 import zlib
 from base64 import standard_b64encode
-from collections import namedtuple
+from functools import lru_cache
 from math import ceil
 from tempfile import NamedTemporaryFile
+from typing import Dict, List, NamedTuple, Optional, Union
 
 from kitty.cli import parse_args
 from kitty.cli_stub import IcatCLIOptions
 from kitty.constants import appname
-from kitty.utils import TTYIO, fit_image, screen_size_function
+from kitty.utils import (
+    TTYIO, ScreenSize, ScreenSizeGetter, fit_image, screen_size_function
+)
 
 from ..tui.images import (
     ConvertFailed, NoImageMagick, OpenFailed, convert, fsenc, identify
@@ -104,27 +107,25 @@ colors. For example, --1 evaluates as -1,073,741,825.
 '''
 
 
-screen_size = None
+screen_size: Optional[ScreenSizeGetter] = None
+can_transfer_with_files = False
 
 
-def get_screen_size_function():
+def get_screen_size_function() -> ScreenSizeGetter:
     global screen_size
     if screen_size is None:
         screen_size = screen_size_function()
     return screen_size
 
 
-def get_screen_size():
+def get_screen_size() -> ScreenSize:
     screen_size = get_screen_size_function()
     return screen_size()
 
 
-def options_spec():
-    if not hasattr(options_spec, 'ans'):
-        options_spec.ans = OPTIONS.format(
-            appname='{}-icat'.format(appname),
-        )
-    return options_spec.ans
+@lru_cache(maxsize=2)
+def options_spec() -> str:
+    return OPTIONS.format(appname='{}-icat'.format(appname))
 
 
 def write_gr_cmd(cmd, payload=None):
@@ -196,7 +197,7 @@ def show(outfile, width, height, zindex, fmt, transmit_mode='t', align='center',
         set_cursor_for_place(place, cmd, width, height, align)
     else:
         set_cursor(cmd, width, height, align)
-    if detect_support.has_files:
+    if can_transfer_with_files:
         cmd['t'] = transmit_mode
         write_gr_cmd(cmd, standard_b64encode(os.path.abspath(outfile).encode(fsenc)))
     else:
@@ -250,20 +251,21 @@ def scan(d):
 
 
 def detect_support(wait_for=10, silent=False):
+    global can_transfer_with_files
     if not silent:
         print('Checking for graphics ({}s max. wait)...'.format(wait_for), end='\r')
     sys.stdout.flush()
     try:
         received = b''
-        responses = {}
+        responses: Dict[int, bool] = {}
 
         def parse_responses():
             for m in re.finditer(b'\033_Gi=([1|2]);(.+?)\033\\\\', received):
                 iid = m.group(1)
                 if iid in (b'1', b'2'):
-                    iid = int(iid.decode('ascii'))
-                    if iid not in responses:
-                        responses[iid] = m.group(2) == b'OK'
+                    iid_ = int(iid.decode('ascii'))
+                    if iid_ not in responses:
+                        responses[iid_] = m.group(2) == b'OK'
 
         def more_needed(data):
             nonlocal received
@@ -280,16 +282,24 @@ def detect_support(wait_for=10, silent=False):
     finally:
         if not silent:
             sys.stdout.buffer.write(b'\033[J'), sys.stdout.flush()
-    detect_support.has_files = bool(responses.get(2))
+    can_transfer_with_files = bool(responses.get(2))
     return responses.get(1, False)
 
 
-def parse_place(raw):
+class Place(NamedTuple):
+    width: int
+    height: int
+    left: int
+    top: int
+
+
+def parse_place(raw: str) -> Optional[Place]:
     if raw:
         area, pos = raw.split('@', 1)
         w, h = map(int, area.split('x'))
         l, t = map(int, pos.split('x'))
-        return namedtuple('Place', 'width height left top')(w, h, l, t)
+        return Place(w, h, l, t)
+    return None
 
 
 help_text = (
@@ -344,10 +354,12 @@ def process_single_item(item, args, url_pat=None, maybe_dir=True):
 
 
 def main(args=sys.argv):
-    args, items = parse_args(args[1:], options_spec, usage, help_text, '{} +kitten icat'.format(appname), result_class=IcatCLIOptions)
+    global can_transfer_with_files
+    args, items_ = parse_args(args[1:], options_spec, usage, help_text, '{} +kitten icat'.format(appname), result_class=IcatCLIOptions)
+    items: List[Union[str, bytes]] = list(items)
 
     if args.print_window_size:
-        screen_size_function.ans = None
+        screen_size_function.cache_clear()
         with open(os.ctermid()) as tty:
             ss = screen_size_function(tty)()
         print('{}x{}'.format(ss.width, ss.height), end='')
@@ -384,16 +396,16 @@ def main(args=sys.argv):
     if args.detect_support:
         if not detect_support(wait_for=args.detection_timeout, silent=True):
             raise SystemExit(1)
-        print('file' if detect_support.has_files else 'stream', end='', file=sys.stderr)
+        print('file' if can_transfer_with_files else 'stream', end='', file=sys.stderr)
         return
     if args.transfer_mode == 'detect':
         if not detect_support(wait_for=args.detection_timeout, silent=args.silent):
             raise SystemExit('This terminal emulator does not support the graphics protocol, use a terminal emulator such as kitty that does support it')
     else:
-        detect_support.has_files = args.transfer_mode == 'file'
+        can_transfer_with_files = args.transfer_mode == 'file'
     errors = []
     if args.clear:
-        sys.stdout.buffer.write(clear_images_on_screen(delete_data=True))
+        sys.stdout.write(clear_images_on_screen(delete_data=True))
         if not items:
             return
     if not items:
diff --git a/kittens/key_demo/main.py b/kittens/key_demo/main.py
index 96fed924a..f59667ef6 100644
--- a/kittens/key_demo/main.py
+++ b/kittens/key_demo/main.py
@@ -28,15 +28,15 @@ class KeysHandler(Handler):
             REPEAT: 'REPEAT',
             RELEASE: 'RELEASE'
         }[key_event.type]
-        mods = []
+        lmods = []
         for m, name in {
                 SHIFT: 'Shift',
                 ALT: 'Alt',
                 CTRL: 'Ctrl',
                 SUPER: 'Super'}.items():
             if key_event.mods & m:
-                mods.append(name)
-        mods = '+'.join(mods)
+                lmods.append(name)
+        mods = '+'.join(lmods)
         if mods:
             mods += '+'
         self.print('Key {}: {}{} [{}]'.format(etype, mods, key_event.key, encode_key_event(key_event)))
diff --git a/kitty/conf/definition.py b/kitty/conf/definition.py
index 7751fb26c..69d553cbe 100644
--- a/kitty/conf/definition.py
+++ b/kitty/conf/definition.py
@@ -207,7 +207,7 @@ def render_block(text):
 def as_conf_file(all_options):
     ans = ['# vim:fileencoding=utf-8:ft=conf:foldmethod=marker', '']
     a = ans.append
-    current_group = None
+    current_group: Optional[Group] = None
     num_open_folds = 0
     all_options = list(all_options)
 
@@ -311,9 +311,10 @@ def as_type_stub(
     all_options: Dict[str, Union[Option, List[Shortcut]]],
     special_types: Optional[Dict[str, str]] = None,
     preamble_lines: Union[Tuple[str, ...], List[str], Iterator[str]] = (),
-    extra_fields: Union[Tuple[Tuple[str, str], ...], List[Tuple[str, str]], Iterator[Tuple[str, str]]] = ()
+    extra_fields: Union[Tuple[Tuple[str, str], ...], List[Tuple[str, str]], Iterator[Tuple[str, str]]] = (),
+    class_name: str = 'Options'
 ) -> str:
-    ans = ['import typing\n'] + list(preamble_lines) + ['', 'class Options:']
+    ans = ['import typing\n'] + list(preamble_lines) + ['', 'class {}:'.format(class_name)]
     imports: Set[Tuple[str, str]] = set()
     overrides = special_types or {}
     for name, val in all_options.items():
@@ -328,14 +329,14 @@ def as_type_stub(
         ans.append('    {}: {}'.format(field_name, type_def))
     ans.append('    def __iter__(self): pass')
     ans.append('    def __len__(self): pass')
-    return '\n'.join(ans)
+    return '\n'.join(ans) + '\n\n\n'
 
 
 def save_type_stub(text: str, fpath: str) -> None:
     import os
-    with open(fpath + 'i', 'w') as f:
-        print(
-            '# Update this file by running: python {}'.format(os.path.relpath(os.path.abspath(fpath))),
-            file=f
-        )
-        f.write(text)
+    fpath += 'i'
+    preamble = '# Update this file by running: python {}\n\n'.format(os.path.relpath(os.path.abspath(fpath)))
+    existing = open(fpath).read()
+    current = preamble + text
+    if existing != current:
+        open(fpath, 'w').write(current)
diff --git a/kitty/options_stub.py b/kitty/options_stub.py
index 49a73b0f5..b0b86d656 100644
--- a/kitty/options_stub.py
+++ b/kitty/options_stub.py
@@ -7,6 +7,9 @@ class Options:
     pass
 
 
+DiffOptions = Options
+
+
 def generate_stub():
     from .config_data import all_options
     from .conf.definition import as_type_stub, save_type_stub
@@ -26,6 +29,10 @@ def generate_stub():
             ('sequence_map', 'SequenceMap'),
         )
     )
+
+    from kittens.diff.config_data import all_options
+    text += as_type_stub(all_options, class_name='DiffOptions')
+
     save_type_stub(text, __file__)
 
 
diff --git a/kitty/utils.py b/kitty/utils.py
index 4de5fd7de..d365a2c08 100644
--- a/kitty/utils.py
+++ b/kitty/utils.py
@@ -10,11 +10,10 @@ import os
 import re
 import string
 import sys
-from collections import namedtuple
 from contextlib import suppress
 from functools import lru_cache
 from time import monotonic
-from typing import Any, Dict, List, Optional, cast
+from typing import Any, Dict, List, NamedTuple, Optional, cast
 
 from .constants import (
     appname, is_macos, is_wayland, shell_path, supports_primary_selection
@@ -81,7 +80,13 @@ def parse_color_set(raw):
             continue
 
 
-ScreenSize = namedtuple('ScreenSize', 'rows cols width height cell_width cell_height')
+class ScreenSize(NamedTuple):
+    rows: int
+    cols: int
+    width: int
+    height: int
+    cell_width: int
+    cell_height: int
 
 
 class ScreenSizeGetter: