diff --git a/kiwi_scp/_constants.py b/kiwi_scp/_constants.py
index 843e901..31de4c9 100644
--- a/kiwi_scp/_constants.py
+++ b/kiwi_scp/_constants.py
@@ -18,7 +18,7 @@ RE_VARNAME = r"^[A-Za-z](?:[A-Za-z0-9\._-]*[A-Za-z0-9])$"
 # location of "kiwi_scp" module
 KIWI_ROOT = os.path.dirname(__file__)
 # default name of kiwi-scp file
-KIWI_CONF_NAME = os.getenv('KIWI_CONF_NAME', "kiwi.yml")
+KIWI_CONF_NAME = os.getenv("KIWI_CONF_NAME", "kiwi.yml")
 # default name of compose files
 COMPOSE_FILE_NAME = "docker-compose.yml"
 
@@ -31,7 +31,7 @@ DEFAULT_KIWI_CONF_NAME = f"{KIWI_ROOT}/data/etc/kiwi_default.yml"
 DEFAULT_DOCKER_COMPOSE_NAME = f"{KIWI_ROOT}/data/etc/docker-compose_default.yml"
 
 # special config directory
-CONF_DIRECTORY_NAME = 'config'
+CONFIG_DIRECTORY_NAME = "config"
 
 # location for auxiliary Dockerfiles
 IMAGES_DIRECTORY_NAME = f"{KIWI_ROOT}/data/images"
@@ -45,5 +45,5 @@ RESERVED_PROJECT_NAMES = [
 # DOCKER IMAGE NAMES
 
 # name for auxiliary docker images
-LOCAL_IMAGES_NAME = 'localhost/kiwi-scp/auxiliary'
-DEFAULT_IMAGE_NAME = 'alpine:latest'
+LOCAL_IMAGES_NAME = "localhost/kiwi-scp/auxiliary"
+DEFAULT_IMAGE_NAME = "alpine:latest"
diff --git a/kiwi_scp/commands/cmd_shell.py b/kiwi_scp/commands/cmd_shell.py
index 65c2f40..2d1ca23 100644
--- a/kiwi_scp/commands/cmd_shell.py
+++ b/kiwi_scp/commands/cmd_shell.py
@@ -39,7 +39,7 @@ class ShellCommand(KiwiCommand):
         # shells from KiwiConfig
         shells = [
             *(str(path) for path in instance.config.shells),
-            # as a last resort, fall back to '/bin/sh' and 'sh'
+            # as a last resort, fall back to "/bin/sh" and "sh"
             "/bin/sh", "sh",
         ]
 
diff --git a/kiwi_scp/rootkit.py b/kiwi_scp/rootkit.py
index 112b078..1be6ab6 100644
--- a/kiwi_scp/rootkit.py
+++ b/kiwi_scp/rootkit.py
@@ -30,12 +30,12 @@ class Rootkit:
     @functools.lru_cache(maxsize=None)
     def __exists(image_tag: str) -> bool:
         ps = DOCKER_EXE.run([
-            'images',
-            '--filter', f"reference={Rootkit.__image_name(image_tag)}",
-            '--format', '{{.Repository}}:{{.Tag}}'
+            "images",
+            "--filter", f"reference={Rootkit.__image_name(image_tag)}",
+            "--format", "{{.Repository}}:{{.Tag}}"
         ], stdout=subprocess.PIPE)
 
-        return str(ps.stdout, 'utf-8').strip() == Rootkit.__image_name(image_tag)
+        return str(ps.stdout, "utf-8").strip() == Rootkit.__image_name(image_tag)
 
     def __build_image(self) -> None:
         if Rootkit.__exists(self.image_tag):
@@ -44,15 +44,15 @@ class Rootkit:
             if self.image_tag is None:
                 _logger.info(f"Pulling image {Rootkit.__image_name(self.image_tag)}")
                 DOCKER_EXE.run([
-                    'pull', Rootkit.__image_name(self.image_tag)
+                    "pull", Rootkit.__image_name(self.image_tag)
                 ], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
 
             else:
                 _logger.info(f"Building image {Rootkit.__image_name(self.image_tag)}")
                 DOCKER_EXE.run([
-                    'build',
-                    '-t', Rootkit.__image_name(self.image_tag),
-                    '-f', f"{IMAGES_DIRECTORY_NAME}/{self.image_tag}.Dockerfile",
+                    "build",
+                    "-t", Rootkit.__image_name(self.image_tag),
+                    "-f", f"{IMAGES_DIRECTORY_NAME}/{self.image_tag}.Dockerfile",
                     f"{IMAGES_DIRECTORY_NAME}"
                 ], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
 
diff --git a/kiwi_scp/yaml.py b/kiwi_scp/yaml.py
index 1b8729c..5caff50 100644
--- a/kiwi_scp/yaml.py
+++ b/kiwi_scp/yaml.py
@@ -25,7 +25,7 @@ class YAML(ruamel.yaml.YAML):
     @staticmethod
     def _format_kiwi_yml(yml_string: str) -> str:
         # insert newline before every main key
-        yml_string = re.sub(r'^(\S)', r'\n\1', yml_string, flags=re.MULTILINE)
+        yml_string = re.sub(r"^(\S)", r"\n\1", yml_string, flags=re.MULTILINE)
 
         # load header comment from file
         with open(HEADER_KIWI_CONF_NAME, 'r') as stream: