diff --git a/docs/conf.py b/docs/conf.py
index c14246c..cc0df9b 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 
 extensions = [
     "jupyterlite_sphinx",
diff --git a/jupyterlite_xeus_python/build.py b/jupyterlite_xeus_python/build.py
index a75ead5..90b7b23 100644
--- a/jupyterlite_xeus_python/build.py
+++ b/jupyterlite_xeus_python/build.py
@@ -1,19 +1,17 @@
 import csv
 import os
-from pathlib import Path
-import requests
 import shutil
+from pathlib import Path
 from subprocess import run
 from tempfile import TemporaryDirectory
-from typing import List
+from typing import List, Optional
 from urllib.parse import urlparse
 
+import requests
+import typer
 import yaml
-
-from empack.pack import pack_env, DEFAULT_CONFIG_PATH
 from empack.file_patterns import PkgFileFilter, pkg_file_filter_from_yaml
-
-import typer
+from empack.pack import DEFAULT_CONFIG_PATH, pack_env
 
 try:
     from mamba.api import create as mamba_create
@@ -164,7 +162,7 @@ def _install_pip_dependencies(prefix_path, dependencies, log=None):
     packages_dist_info = Path(pkg_dir.name).glob("*.dist-info")
 
     for package_dist_info in packages_dist_info:
-        with open(package_dist_info / "RECORD", "r") as record:
+        with open(package_dist_info / "RECORD") as record:
             record_content = record.read()
             record_csv = csv.reader(record_content.splitlines())
             all_files = [_file[0] for _file in record_csv]
@@ -179,7 +177,7 @@ def _install_pip_dependencies(prefix_path, dependencies, log=None):
         with open(package_dist_info / "RECORD", "w") as record:
             record.write(fixed_record_data)
 
-        non_supported_files = [".so", ".a", ".dylib", ".lib", ".exe" ".dll"]
+        non_supported_files = [".so", ".a", ".dylib", ".lib", ".exe.dll"]
 
         # COPY files under `prefix_path`
         for _file, inside_site_packages in files:
@@ -209,7 +207,7 @@ def _install_pip_dependencies(prefix_path, dependencies, log=None):
 def build_and_pack_emscripten_env(
     python_version: str = PYTHON_VERSION,
     xeus_python_version: str = XEUS_PYTHON_VERSION,
-    packages: List[str] = [],
+    packages: Optional[List[str]] = None,
     environment_file: str = "",
     root_prefix: str = "/tmp/xeus-python-kernel",
     env_name: str = "xeus-python-kernel",
@@ -220,6 +218,8 @@ def build_and_pack_emscripten_env(
     log=None,
 ):
     """Build a conda environment for the emscripten platform and pack it with empack."""
+    if packages is None:
+        packages = []
     channels = CHANNELS
     specs = [
         f"python={python_version}",
@@ -324,7 +324,7 @@ def build_and_pack_emscripten_env(
                 dirs_exist_ok=True,
             )
 
-            with open(Path(output_path) / "worker.ts", "r") as fobj:
+            with open(Path(output_path) / "worker.ts") as fobj:
                 worker = fobj.read()
 
             worker = worker.replace("XEUS_KERNEL_FILE", "'xpython_wasm.js'")
diff --git a/jupyterlite_xeus_python/env_build_addon.py b/jupyterlite_xeus_python/env_build_addon.py
index f185ed1..02d6d93 100644
--- a/jupyterlite_xeus_python/env_build_addon.py
+++ b/jupyterlite_xeus_python/env_build_addon.py
@@ -4,16 +4,15 @@
 from pathlib import Path
 from tempfile import TemporaryDirectory
 
-from traitlets import List, Unicode
-
+from jupyterlite_core.addons.federated_extensions import FederatedExtensionAddon
 from jupyterlite_core.constants import (
-    SHARE_LABEXTENSIONS,
-    LAB_EXTENSIONS,
+    FEDERATED_EXTENSIONS,
     JUPYTERLITE_JSON,
+    LAB_EXTENSIONS,
+    SHARE_LABEXTENSIONS,
     UTF8,
-    FEDERATED_EXTENSIONS,
 )
-from jupyterlite_core.addons.federated_extensions import FederatedExtensionAddon
+from traitlets import List, Unicode
 
 from .build import XEUS_PYTHON_VERSION, build_and_pack_emscripten_env
 
@@ -54,7 +53,7 @@ class XeusPythonEnv(FederatedExtensionAddon):
     )
 
     def __init__(self, *args, **kwargs):
-        super(XeusPythonEnv, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
         self.cwd = TemporaryDirectory()
 
diff --git a/tests/test_xeus_python_env.py b/tests/test_xeus_python_env.py
index 65c2806..4bf32c5 100644
--- a/tests/test_xeus_python_env.py
+++ b/tests/test_xeus_python_env.py
@@ -1,11 +1,9 @@
 """Test creating Python envs for jupyterlite-xeus-python."""
 
 import os
-from tempfile import TemporaryDirectory
 from pathlib import Path
 
 import pytest
-
 from jupyterlite_core.app import LiteStatusApp
 
 from jupyterlite_xeus_python.env_build_addon import XeusPythonEnv
@@ -19,7 +17,7 @@ def test_python_env():
     addon = XeusPythonEnv(manager)
     addon.packages = ["numpy", "ipyleaflet"]
 
-    for step in addon.post_build(manager):
+    for _step in addon.post_build(manager):
         pass
 
     # Check env
@@ -42,7 +40,7 @@ def test_python_env_from_file_1():
     addon = XeusPythonEnv(manager)
     addon.environment_file = "environment-1.yml"
 
-    for step in addon.post_build(manager):
+    for _step in addon.post_build(manager):
         pass
 
     # Check env
@@ -88,7 +86,7 @@ def test_python_env_from_file_3():
     addon = XeusPythonEnv(manager)
     addon.environment_file = "test_package/environment-3.yml"
 
-    for step in addon.post_build(manager):
+    for _step in addon.post_build(manager):
         pass
 
     # Test
@@ -111,5 +109,5 @@ def test_python_env_from_file_2():
     addon.environment_file = "environment-2.yml"
 
     with pytest.raises(RuntimeError, match="Cannot install binary PyPI package"):
-        for step in addon.post_build(manager):
+        for _step in addon.post_build(manager):
             pass