@@ -25,6 +25,10 @@ exclude_lines =
     ^\s*return NotImplemented\b
     ^\s*raise$
 
+    # Ignore typing-related things
+    ^if (False|TYPE_CHECKING):
+    : \.\.\.$
+
     # Don't complain if non-runnable code isn't run:
     ^if __name__ == ['"]__main__['"]:$
 
 
@@ -3,6 +3,10 @@
 import logging
 import pipes
 import sys
+from typing import Any
+from typing import Dict
+from typing import Optional
+from typing import Sequence
 
 import cfgv
 from aspy.yaml import ordered_load
@@ -18,15 +22,15 @@
 check_string_regex = cfgv.check_and(cfgv.check_string, cfgv.check_regex)
 
 
-def check_type_tag(tag):
+def check_type_tag(tag: str) -> None:
     if tag not in ALL_TAGS:
         raise cfgv.ValidationError(
             'Type tag {!r} is not recognized.  '
             'Try upgrading identify and pre-commit?'.format(tag),
         )
 
 
-def check_min_version(version):
+def check_min_version(version: str) -> None:
     if parse_version(version) > parse_version(C.VERSION):
         raise cfgv.ValidationError(
             'pre-commit version {} is required but version {} is installed.  '
@@ -36,7 +40,7 @@ def check_min_version(version):
         )
 
 
-def _make_argparser(filenames_help):
+def _make_argparser(filenames_help: str) -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser()
     parser.add_argument('filenames', nargs='*', help=filenames_help)
     parser.add_argument('-V', '--version', action='version', version=C.VERSION)
@@ -86,7 +90,7 @@ class InvalidManifestError(FatalError):
 )
 
 
-def validate_manifest_main(argv=None):
+def validate_manifest_main(argv: Optional[Sequence[str]] = None) -> int:
     parser = _make_argparser('Manifest filenames.')
     args = parser.parse_args(argv)
     ret = 0
@@ -107,15 +111,15 @@ class MigrateShaToRev:
     key = 'rev'
 
     @staticmethod
-    def _cond(key):
+    def _cond(key: str) -> cfgv.Conditional:
         return cfgv.Conditional(
             key, cfgv.check_string,
             condition_key='repo',
             condition_value=cfgv.NotIn(LOCAL, META),
             ensure_absent=True,
         )
 
-    def check(self, dct):
+    def check(self, dct: Dict[str, Any]) -> None:
         if dct.get('repo') in {LOCAL, META}:
             self._cond('rev').check(dct)
             self._cond('sha').check(dct)
@@ -126,14 +130,14 @@ def check(self, dct):
         else:
             self._cond('rev').check(dct)
 
-    def apply_default(self, dct):
+    def apply_default(self, dct: Dict[str, Any]) -> None:
         if 'sha' in dct:
             dct['rev'] = dct.pop('sha')
 
     remove_default = cfgv.Required.remove_default
 
 
-def _entry(modname):
+def _entry(modname: str) -> str:
     """the hook `entry` is passed through `shlex.split()` by the command
     runner, so to prevent issues with spaces and backslashes (on Windows)
     it must be quoted here.
@@ -143,13 +147,21 @@ def _entry(modname):
     )
 
 
-def warn_unknown_keys_root(extra, orig_keys, dct):
+def warn_unknown_keys_root(
+        extra: Sequence[str],
+        orig_keys: Sequence[str],
+        dct: Dict[str, str],
+) -> None:
     logger.warning(
         'Unexpected key(s) present at root: {}'.format(', '.join(extra)),
     )
 
 
-def warn_unknown_keys_repo(extra, orig_keys, dct):
+def warn_unknown_keys_repo(
+        extra: Sequence[str],
+        orig_keys: Sequence[str],
+        dct: Dict[str, str],
+) -> None:
     logger.warning(
         'Unexpected key(s) present on {}: {}'.format(
             dct['repo'], ', '.join(extra),
@@ -281,7 +293,7 @@ class InvalidConfigError(FatalError):
     pass
 
 
-def ordered_load_normalize_legacy_config(contents):
+def ordered_load_normalize_legacy_config(contents: str) -> Dict[str, Any]:
     data = ordered_load(contents)
     if isinstance(data, list):
         # TODO: Once happy, issue a deprecation warning and instructions
@@ -298,7 +310,7 @@ def ordered_load_normalize_legacy_config(contents):
 )
 
 
-def validate_config_main(argv=None):
+def validate_config_main(argv: Optional[Sequence[str]] = None) -> int:
     parser = _make_argparser('Config filenames.')
     args = parser.parse_args(argv)
     ret = 0
 
@@ -21,7 +21,7 @@ class InvalidColorSetting(ValueError):
     pass
 
 
-def format_color(text, color, use_color_setting):
+def format_color(text: str, color: str, use_color_setting: bool) -> str:
     """Format text with color.
 
     Args:
@@ -38,7 +38,7 @@ def format_color(text, color, use_color_setting):
 COLOR_CHOICES = ('auto', 'always', 'never')
 
 
-def use_color(setting):
+def use_color(setting: str) -> bool:
     """Choose whether to use color based on the command argument.
 
     Args:
 
@@ -1,8 +1,12 @@
-import collections
 import os.path
 import re
+from typing import Any
+from typing import Dict
 from typing import List
+from typing import NamedTuple
 from typing import Optional
+from typing import Sequence
+from typing import Tuple
 
 from aspy.yaml import ordered_dump
 from aspy.yaml import ordered_load
@@ -16,20 +20,23 @@
 from pre_commit.clientlib import LOCAL
 from pre_commit.clientlib import META
 from pre_commit.commands.migrate_config import migrate_config
+from pre_commit.store import Store
 from pre_commit.util import CalledProcessError
 from pre_commit.util import cmd_output
 from pre_commit.util import cmd_output_b
 from pre_commit.util import tmpdir
 
 
-class RevInfo(collections.namedtuple('RevInfo', ('repo', 'rev', 'frozen'))):
-    __slots__ = ()
+class RevInfo(NamedTuple):
+    repo: str
+    rev: str
+    frozen: Optional[str]
 
     @classmethod
-    def from_config(cls, config):
+    def from_config(cls, config: Dict[str, Any]) -> 'RevInfo':
         return cls(config['repo'], config['rev'], None)
 
-    def update(self, tags_only, freeze):
+    def update(self, tags_only: bool, freeze: bool) -> 'RevInfo':
         if tags_only:
             tag_cmd = ('git', 'describe', 'FETCH_HEAD', '--tags', '--abbrev=0')
         else:
@@ -57,7 +64,11 @@ class RepositoryCannotBeUpdatedError(RuntimeError):
     pass
 
 
-def _check_hooks_still_exist_at_rev(repo_config, info, store):
+def _check_hooks_still_exist_at_rev(
+        repo_config: Dict[str, Any],
+        info: RevInfo,
+        store: Store,
+) -> None:
     try:
         path = store.clone(repo_config['repo'], info.rev)
         manifest = load_manifest(os.path.join(path, C.MANIFEST_FILE))
@@ -78,7 +89,11 @@ def _check_hooks_still_exist_at_rev(repo_config, info, store):
 REV_LINE_FMT = '{}rev:{}{}{}{}'
 
 
-def _original_lines(path, rev_infos, retry=False):
+def _original_lines(
+        path: str,
+        rev_infos: List[Optional[RevInfo]],
+        retry: bool = False,
+) -> Tuple[List[str], List[int]]:
     """detect `rev:` lines or reformat the file"""
     with open(path) as f:
         original = f.read()
@@ -95,7 +110,7 @@ def _original_lines(path, rev_infos, retry=False):
         return _original_lines(path, rev_infos, retry=True)
 
 
-def _write_new_config(path, rev_infos):
+def _write_new_config(path: str, rev_infos: List[Optional[RevInfo]]) -> None:
     lines, idxs = _original_lines(path, rev_infos)
 
     for idx, rev_info in zip(idxs, rev_infos):
@@ -119,7 +134,13 @@ def _write_new_config(path, rev_infos):
         f.write(''.join(lines))
 
 
-def autoupdate(config_file, store, tags_only, freeze, repos=()):
+def autoupdate(
+        config_file: str,
+        store: Store,
+        tags_only: bool,
+        freeze: bool,
+        repos: Sequence[str] = (),
+) -> int:
     """Auto-update the pre-commit config to the latest versions of repos."""
     migrate_config(config_file, quiet=True)
     retv = 0
 
@@ -1,10 +1,11 @@
 import os.path
 
 from pre_commit import output
+from pre_commit.store import Store
 from pre_commit.util import rmtree
 
 
-def clean(store):
+def clean(store: Store) -> int:
     legacy_path = os.path.expanduser('~/.pre-commit')
     for directory in (store.directory, legacy_path):
         if os.path.exists(directory):
 
@@ -1,4 +1,8 @@
 import os.path
+from typing import Any
+from typing import Dict
+from typing import Set
+from typing import Tuple
 
 import pre_commit.constants as C
 from pre_commit import output
@@ -8,9 +12,15 @@
 from pre_commit.clientlib import load_manifest
 from pre_commit.clientlib import LOCAL
 from pre_commit.clientlib import META
+from pre_commit.store import Store
 
 
-def _mark_used_repos(store, all_repos, unused_repos, repo):
+def _mark_used_repos(
+        store: Store,
+        all_repos: Dict[Tuple[str, str], str],
+        unused_repos: Set[Tuple[str, str]],
+        repo: Dict[str, Any],
+) -> None:
     if repo['repo'] == META:
         return
     elif repo['repo'] == LOCAL:
@@ -47,7 +57,7 @@ def _mark_used_repos(store, all_repos, unused_repos, repo):
             ))
 
 
-def _gc_repos(store):
+def _gc_repos(store: Store) -> int:
     configs = store.select_all_configs()
     repos = store.select_all_repos()
 
@@ -73,7 +83,7 @@ def _gc_repos(store):
     return len(unused_repos)
 
 
-def gc(store):
+def gc(store: Store) -> int:
     with store.exclusive_lock():
         repos_removed = _gc_repos(store)
     output.write_line(f'{repos_removed} repo(s) removed.')
 
@@ -1,14 +1,21 @@
 import logging
 import os.path
+from typing import Sequence
 
 from pre_commit.commands.install_uninstall import install
+from pre_commit.store import Store
 from pre_commit.util import CalledProcessError
 from pre_commit.util import cmd_output
 
 logger = logging.getLogger('pre_commit')
 
 
-def init_templatedir(config_file, store, directory, hook_types):
+def init_templatedir(
+        config_file: str,
+        store: Store,
+        directory: str,
+        hook_types: Sequence[str],
+) -> int:
     install(
         config_file, store, hook_types=hook_types,
         overwrite=True, skip_on_missing_config=True, git_dir=directory,
@@ -25,3 +32,4 @@ def init_templatedir(config_file, store, directory, hook_types):
         logger.warning(
             f'maybe `git config --global init.templateDir {dest}`?',
         )
+    return 0