diff --git a/dev_requirements.txt b/dev_requirements.txt
--- a/dev_requirements.txt
+++ b/dev_requirements.txt
@@ -5,5 +5,5 @@ pytest-localserver >= 0.5.0, < 0.6
 mock >= 3.0.0, < 4.1
 Sphinx >= 1.8.0, < 3.1
 WebTest >= 2.0.6, < 2.1
-isort == 4.3.21
+isort == 5.1.2
 pyflakes == 2.2.0
diff --git a/kallithea/config/app_cfg.py b/kallithea/config/app_cfg.py
--- a/kallithea/config/app_cfg.py
+++ b/kallithea/config/app_cfg.py
@@ -86,8 +86,8 @@ base_config.update_blueprint({
 # 'debug = true' (not in production!)
 # See the Kallithea documentation for more information.
 try:
+    import kajiki  # only to check its existence
     from tgext.debugbar import enable_debugbar
-    import kajiki # only to check its existence
     assert kajiki
 except ImportError:
     pass
diff --git a/kallithea/controllers/compare.py b/kallithea/controllers/compare.py
--- a/kallithea/controllers/compare.py
+++ b/kallithea/controllers/compare.py
@@ -130,8 +130,8 @@ class CompareController(BaseRepoControll
 
         elif alias == 'git':
             if org_repo != other_repo:
+                from dulwich.client import SubprocessGitClient
                 from dulwich.repo import Repo
-                from dulwich.client import SubprocessGitClient
 
                 gitrepo = Repo(org_repo.path)
                 SubprocessGitClient(thin_packs=False).fetch(other_repo.path, gitrepo)
diff --git a/kallithea/lib/celerylib/tasks.py b/kallithea/lib/celerylib/tasks.py
--- a/kallithea/lib/celerylib/tasks.py
+++ b/kallithea/lib/celerylib/tasks.py
@@ -323,8 +323,8 @@ def send_email(recipients, subject, body
 @celerylib.task
 @celerylib.dbsession
 def create_repo(form_data, cur_user):
+    from kallithea.model.db import Setting
     from kallithea.model.repo import RepoModel
-    from kallithea.model.db import Setting
 
     DBS = celerylib.get_session()
 
diff --git a/kallithea/lib/db_manage.py b/kallithea/lib/db_manage.py
--- a/kallithea/lib/db_manage.py
+++ b/kallithea/lib/db_manage.py
@@ -163,11 +163,9 @@ class DbManage(object):
             self.create_user(username, password, email, True)
         else:
             log.info('creating admin and regular test users')
-            from kallithea.tests.base import TEST_USER_ADMIN_LOGIN, \
-                TEST_USER_ADMIN_PASS, TEST_USER_ADMIN_EMAIL, \
-                TEST_USER_REGULAR_LOGIN, TEST_USER_REGULAR_PASS, \
-                TEST_USER_REGULAR_EMAIL, TEST_USER_REGULAR2_LOGIN, \
-                TEST_USER_REGULAR2_PASS, TEST_USER_REGULAR2_EMAIL
+            from kallithea.tests.base import (TEST_USER_ADMIN_EMAIL, TEST_USER_ADMIN_LOGIN, TEST_USER_ADMIN_PASS, TEST_USER_REGULAR2_EMAIL,
+                                              TEST_USER_REGULAR2_LOGIN, TEST_USER_REGULAR2_PASS, TEST_USER_REGULAR_EMAIL, TEST_USER_REGULAR_LOGIN,
+                                              TEST_USER_REGULAR_PASS)
 
             self.create_user(TEST_USER_ADMIN_LOGIN, TEST_USER_ADMIN_PASS,
                              TEST_USER_ADMIN_EMAIL, True)
diff --git a/kallithea/lib/helpers.py b/kallithea/lib/helpers.py
--- a/kallithea/lib/helpers.py
+++ b/kallithea/lib/helpers.py
@@ -632,6 +632,7 @@ def person(author, show_attr="username")
     """Find the user identified by 'author', return one of the users attributes,
     default to the username attribute, None if there is no user"""
     from kallithea.model.db import User
+
     # if author is already an instance use it for extraction
     if isinstance(author, User):
         return getattr(author, show_attr)
@@ -646,6 +647,7 @@ def person(author, show_attr="username")
 
 def person_by_id(id_, show_attr="username"):
     from kallithea.model.db import User
+
     # maybe it's an ID ?
     if str(id_).isdigit() or isinstance(id_, int):
         id_ = int(id_)
@@ -974,10 +976,8 @@ def gravatar(email_address, cls='', size
 
 
 def gravatar_url(email_address, size=30, default=''):
-    # doh, we need to re-import those to mock it later
-    from kallithea.config.routing import url
-    from kallithea.model.db import User
     from tg import tmpl_context as c
+
     if not c.visual.use_gravatar:
         return ""
 
@@ -987,6 +987,10 @@ def gravatar_url(email_address, size=30,
     if email_address == _def:
         return default
 
+    # re-import url so tests can mock it
+    from kallithea.config.routing import url
+    from kallithea.model.db import User
+
     parsed_url = urllib.parse.urlparse(url.current(qualified=True))
     url = (c.visual.gravatar_url or User.DEFAULT_GRAVATAR_URL) \
                .replace('{email}', email_address) \
@@ -1022,8 +1026,7 @@ def fancy_file_stats(stats):
 
     :param stats: two element list of added/deleted lines of code
     """
-    from kallithea.lib.diffs import NEW_FILENODE, DEL_FILENODE, \
-        MOD_FILENODE, RENAMED_FILENODE, CHMOD_FILENODE, BIN_FILENODE
+    from kallithea.lib.diffs import BIN_FILENODE, CHMOD_FILENODE, DEL_FILENODE, MOD_FILENODE, NEW_FILENODE, RENAMED_FILENODE
 
     a, d = stats['added'], stats['deleted']
     width = 100
diff --git a/kallithea/lib/hooks.py b/kallithea/lib/hooks.py
--- a/kallithea/lib/hooks.py
+++ b/kallithea/lib/hooks.py
@@ -307,6 +307,7 @@ def _hook_environment(repo_path):
     connect to the database.
     """
     import paste.deploy
+
     import kallithea.config.application
 
     extras = get_hook_environment()
diff --git a/kallithea/lib/middleware/pygrack.py b/kallithea/lib/middleware/pygrack.py
--- a/kallithea/lib/middleware/pygrack.py
+++ b/kallithea/lib/middleware/pygrack.py
@@ -168,8 +168,9 @@ class GitRepository(object):
         if git_command in ['git-receive-pack']:
             # updating refs manually after each push.
             # Needed for pre-1.7.0.4 git clients using regular HTTP mode.
+            from dulwich.server import update_server_info
+
             from kallithea.lib.vcs import get_repo
-            from dulwich.server import update_server_info
             repo = get_repo(self.content_path)
             if repo:
                 update_server_info(repo._repo)
@@ -223,6 +224,6 @@ class GitDirectory(object):
 
 
 def make_wsgi_app(repo_name, repo_root):
-    from dulwich.web import LimitedInputFilter, GunzipFilter
+    from dulwich.web import GunzipFilter, LimitedInputFilter
     app = GitDirectory(repo_root, repo_name)
     return GunzipFilter(LimitedInputFilter(app))
diff --git a/kallithea/lib/utils2.py b/kallithea/lib/utils2.py
--- a/kallithea/lib/utils2.py
+++ b/kallithea/lib/utils2.py
@@ -331,9 +331,8 @@ def get_changeset_safe(repo, rev):
     :param repo:
     :param rev:
     """
-    from kallithea.lib.vcs.backends.base import BaseRepository
+    from kallithea.lib.vcs.backends.base import BaseRepository, EmptyChangeset
     from kallithea.lib.vcs.exceptions import RepositoryError
-    from kallithea.lib.vcs.backends.base import EmptyChangeset
     if not isinstance(repo, BaseRepository):
         raise Exception('You must pass an Repository '
                         'object as first argument got %s' % type(repo))
diff --git a/kallithea/lib/vcs/utils/helpers.py b/kallithea/lib/vcs/utils/helpers.py
--- a/kallithea/lib/vcs/utils/helpers.py
+++ b/kallithea/lib/vcs/utils/helpers.py
@@ -108,8 +108,8 @@ def get_highlighted_code(name, code, typ
     except ImportError:
         return code
     from pygments import highlight
-    from pygments.lexers import guess_lexer_for_filename, ClassNotFound
     from pygments.formatters import TerminalFormatter
+    from pygments.lexers import ClassNotFound, guess_lexer_for_filename
 
     try:
         lexer = guess_lexer_for_filename(name, code)
diff --git a/kallithea/model/db.py b/kallithea/model/db.py
--- a/kallithea/model/db.py
+++ b/kallithea/model/db.py
@@ -307,8 +307,10 @@ class Setting(Base, BaseDbModel):
 
     @classmethod
     def get_server_info(cls):
+        import platform
+
         import pkg_resources
-        import platform
+
         from kallithea.lib.utils import check_git_version
         mods = [(p.project_name, p.version) for p in pkg_resources.working_set]
         info = {
@@ -595,7 +597,8 @@ class User(Base, BaseDbModel):
 
         :param author:
         """
-        from kallithea.lib.helpers import email, author_name
+        from kallithea.lib.helpers import author_name, email
+
         # Valid email in the attribute passed, see if they're in the system
         _email = email(author)
         if _email:
diff --git a/kallithea/model/repo.py b/kallithea/model/repo.py
--- a/kallithea/model/repo.py
+++ b/kallithea/model/repo.py
@@ -109,7 +109,8 @@ class RepoModel(object):
 
     @classmethod
     def _render_datatable(cls, tmpl, *args, **kwargs):
-        from tg import tmpl_context as c, request, app_globals
+        from tg import app_globals, request
+        from tg import tmpl_context as c
         from tg.i18n import ugettext as _
 
         _tmpl_lookup = app_globals.mako_lookup
@@ -128,7 +129,9 @@ class RepoModel(object):
         admin: return data for action column.
         """
         _render = self._render_datatable
-        from tg import tmpl_context as c, request
+        from tg import request
+        from tg import tmpl_context as c
+
         from kallithea.model.scm import ScmModel
 
         def repo_lnk(name, rtype, rstate, private, fork_of):
diff --git a/kallithea/model/repo_group.py b/kallithea/model/repo_group.py
--- a/kallithea/model/repo_group.py
+++ b/kallithea/model/repo_group.py
@@ -189,8 +189,8 @@ class RepoGroupModel(object):
     def _update_permissions(self, repo_group, perms_new=None,
                             perms_updates=None, recursive=None,
                             check_perms=True):
+        from kallithea.lib.auth import HasUserGroupPermissionLevel
         from kallithea.model.repo import RepoModel
-        from kallithea.lib.auth import HasUserGroupPermissionLevel
 
         if not perms_new:
             perms_new = []
diff --git a/kallithea/model/user.py b/kallithea/model/user.py
--- a/kallithea/model/user.py
+++ b/kallithea/model/user.py
@@ -59,8 +59,7 @@ class UserModel(object):
         if not cur_user:
             cur_user = getattr(get_current_authuser(), 'username', None)
 
-        from kallithea.lib.hooks import log_create_user, \
-            check_allowed_create_user
+        from kallithea.lib.hooks import check_allowed_create_user, log_create_user
         _fd = form_data
         user_data = {
             'username': _fd['username'],
@@ -111,9 +110,8 @@ class UserModel(object):
         if not cur_user:
             cur_user = getattr(get_current_authuser(), 'username', None)
 
-        from kallithea.lib.auth import get_crypt_password, check_password
-        from kallithea.lib.hooks import log_create_user, \
-            check_allowed_create_user
+        from kallithea.lib.auth import check_password, get_crypt_password
+        from kallithea.lib.hooks import check_allowed_create_user, log_create_user
         user_data = {
             'username': username, 'password': password,
             'email': email, 'firstname': firstname, 'lastname': lastname,
@@ -168,8 +166,8 @@ class UserModel(object):
             raise
 
     def create_registration(self, form_data):
+        import kallithea.lib.helpers as h
         from kallithea.model.notification import NotificationModel
-        import kallithea.lib.helpers as h
 
         form_data['admin'] = False
         form_data['extern_type'] = User.DEFAULT_AUTH_TYPE
@@ -317,9 +315,9 @@ class UserModel(object):
         allowing users to copy-paste or manually enter the token from the
         email.
         """
+        import kallithea.lib.helpers as h
         from kallithea.lib.celerylib import tasks
         from kallithea.model.notification import EmailNotificationModel
-        import kallithea.lib.helpers as h
 
         user_email = data['email']
         user = User.get_by_email(user_email)
@@ -386,8 +384,8 @@ class UserModel(object):
         return expected_token == token
 
     def reset_password(self, user_email, new_passwd):
+        from kallithea.lib import auth
         from kallithea.lib.celerylib import tasks
-        from kallithea.lib import auth
         user = User.get_by_email(user_email)
         if user is not None:
             if not self.can_change_password(user):
diff --git a/kallithea/tests/api/api_base.py b/kallithea/tests/api/api_base.py
--- a/kallithea/tests/api/api_base.py
+++ b/kallithea/tests/api/api_base.py
@@ -145,7 +145,7 @@ class _BaseTestApi(object):
         assert 'trololo' == Optional.extract('trololo')
 
     def test_Optional_OAttr(self):
-        from kallithea.controllers.api.api import Optional, OAttr
+        from kallithea.controllers.api.api import OAttr, Optional
 
         option1 = Optional(OAttr('apiuser'))
         assert 'apiuser' == Optional.extract(option1)
diff --git a/kallithea/tests/other/test_libs.py b/kallithea/tests/other/test_libs.py
--- a/kallithea/tests/other/test_libs.py
+++ b/kallithea/tests/other/test_libs.py
@@ -156,8 +156,9 @@ class TestLibs(base.TestController):
         (dict(years= -3, months= -2), '3 years and 2 months ago'),
     ])
     def test_age(self, age_args, expected):
+        from dateutil import relativedelta
+
         from kallithea.lib.utils2 import age
-        from dateutil import relativedelta
         with test_context(self.app):
             n = datetime.datetime(year=2012, month=5, day=17)
             delt = lambda *args, **kwargs: relativedelta.relativedelta(*args, **kwargs)
@@ -181,8 +182,9 @@ class TestLibs(base.TestController):
         (dict(years= -4, months= -8), '5 years ago'),
     ])
     def test_age_short(self, age_args, expected):
+        from dateutil import relativedelta
+
         from kallithea.lib.utils2 import age
-        from dateutil import relativedelta
         with test_context(self.app):
             n = datetime.datetime(year=2012, month=5, day=17)
             delt = lambda *args, **kwargs: relativedelta.relativedelta(*args, **kwargs)
@@ -200,8 +202,9 @@ class TestLibs(base.TestController):
         (dict(years=1, months=1), 'in 1 year and 1 month')
     ])
     def test_age_in_future(self, age_args, expected):
+        from dateutil import relativedelta
+
         from kallithea.lib.utils2 import age
-        from dateutil import relativedelta
         with test_context(self.app):
             n = datetime.datetime(year=2012, month=5, day=17)
             delt = lambda *args, **kwargs: relativedelta.relativedelta(*args, **kwargs)
@@ -297,6 +300,7 @@ class TestLibs(base.TestController):
         :param text:
         """
         import re
+
         # quickly change expected url[] into a link
         url_pattern = re.compile(r'(?:url\[)(.+?)(?:\])')
 
@@ -570,11 +574,11 @@ class TestLibs(base.TestController):
         ('http://www.example.org/kallithea/repos/', 'abc/xyz/', 'http://www.example.org/kallithea/repos/abc/xyz/'),
     ])
     def test_canonical_url(self, canonical, test, expected):
-        from kallithea.lib.helpers import canonical_url
+        # setup url(), used by canonical_url
+        import routes
         from tg import request
 
-        # setup url(), used by canonical_url
-        import routes
+        from kallithea.lib.helpers import canonical_url
         m = routes.Mapper()
         m.connect('about', '/about-page')
         url = routes.URLGenerator(m, {'HTTP_HOST': 'http_host.example.org'})
@@ -594,11 +598,12 @@ class TestLibs(base.TestController):
         ('http://www.example.org/kallithea/repos/', 'www.example.org'),
     ])
     def test_canonical_hostname(self, canonical, expected):
-        from kallithea.lib.helpers import canonical_hostname
+        import routes
         from tg import request
 
+        from kallithea.lib.helpers import canonical_hostname
+
         # setup url(), used by canonical_hostname
-        import routes
         m = routes.Mapper()
         url = routes.URLGenerator(m, {'HTTP_HOST': 'http_host.example.org'})
 
diff --git a/kallithea/tests/vcs/test_workdirs.py b/kallithea/tests/vcs/test_workdirs.py
--- a/kallithea/tests/vcs/test_workdirs.py
+++ b/kallithea/tests/vcs/test_workdirs.py
@@ -68,6 +68,7 @@ class WorkdirTestCaseMixin(_BackendTestM
 
     def test_checkout_branch(self):
         from kallithea.lib.vcs.exceptions import BranchDoesNotExistError
+
         # first, 'foobranch' does not exist.
         with pytest.raises(BranchDoesNotExistError):
             self.repo.workdir.checkout_branch(branch='foobranch')
diff --git a/scripts/i18n b/scripts/i18n
--- a/scripts/i18n
+++ b/scripts/i18n
@@ -19,7 +19,6 @@ import shutil
 import sys
 
 import click
-
 import i18n_utils
 
 
@@ -90,11 +89,8 @@ def normalized_merge(local, base, other,
 
     and then invoke merge/rebase/graft with the additional argument '--tool i18n'.
     """
-    from mercurial import (
-        context,
-        simplemerge,
-        ui as uimod,
-    )
+    from mercurial import context, simplemerge
+    from mercurial import ui as uimod
 
     print('i18n normalized-merge: normalizing and merging %s' % output)