Fix pylint issues

Change-Id: I2bf1a1752693f2600e0fe62e30300e04706b6546
diff --git a/src/charm.py b/src/charm.py
index d56b608..67e0f34 100755
--- a/src/charm.py
+++ b/src/charm.py
@@ -14,14 +14,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+"""A StorPool backend charm for Cinder"""
+
 import dataclasses
 import logging
 import pathlib
 
-from ops_openstack.plugins.classes import CinderStoragePluginCharm
-from ops_openstack.core import charm_class, get_charm_class
 from ops.main import main
 from ops.model import BlockedStatus
+from ops_openstack.core import charm_class, get_charm_class
+from ops_openstack.plugins.classes import CinderStoragePluginCharm
 
 logger = logging.getLogger(__name__)
 
@@ -38,18 +40,23 @@
 
     @classmethod
     def from_config(cls, data) -> "StorPoolConfItems":
+        """Create an object from an options dictionary"""
         args = {
             field.name: str(data[field.name.replace("_", "-")]) for field in dataclasses.fields(cls)
         }
         return cls(**args)
 
     def to_ini_key_value_pairs(self) -> str:
+        """Serialize to ini-style key-value pairs"""
         return "".join(
             f"{name.upper()}={value}\n" for name, value in dataclasses.asdict(self).items()
         )
 
 
 class CinderCharmBase(CinderStoragePluginCharm):
+    """
+    Base class for the StorPool charm
+    """
 
     PACKAGES = ["charm-cinder-storpool-deps", "cinder-common"]
     MANDATORY_CONFIG = [
@@ -64,9 +71,6 @@
     stateless = True
     active_active = True
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-
     def on_config(self, event):
         config = dict(self.framework.model.config)
         conf_error = self._check_for_config_errors(config)
@@ -83,8 +87,12 @@
 
         self._stored.is_started = True
 
-    def cinder_configuration(self, config):
-        conf_error = self._check_for_config_errors(config)
+    def custom_status_check(self):
+        """Overriding abstract, which is not used anywhere"""
+        return BlockedStatus("Should not be here")
+
+    def cinder_configuration(self, charm_config):
+        conf_error = self._check_for_config_errors(charm_config)
         if conf_error is not None:
             logger.error(conf_error)
             self._stored.is_started = False
@@ -92,21 +100,21 @@
             return []
 
         # Return the configuration to be set by the principal.
-        backend_name = config.get("volume-backend-name", self.framework.model.app.name)
+        backend_name = charm_config.get("volume-backend-name", self.framework.model.app.name)
         volume_driver = "cinder.volume.drivers.storpool.StorPoolDriver"
 
         options = [
             ("volume_driver", volume_driver),
             ("volume_backend_name", backend_name),
-            ("storpool_template", config["storpool-template"]),
-            ("sp_api_http_host", config["sp-api-http-host"]),
-            ("sp_api_http_port", config["sp-api-http-port"]),
-            ("sp_auth_token", config["sp-auth-token"]),
+            ("storpool_template", charm_config["storpool-template"]),
+            ("sp_api_http_host", charm_config["sp-api-http-host"]),
+            ("sp_api_http_port", charm_config["sp-api-http-port"]),
+            ("sp_auth_token", charm_config["sp-auth-token"]),
             ("iscsi_export_to", "*"),
-            ("iscsi_portal_group", config["iscsi-portal-group"]),
+            ("iscsi_portal_group", charm_config["iscsi-portal-group"]),
         ]
 
-        if config.get("use-multipath"):
+        if charm_config.get("use-multipath"):
             options.extend(
                 [
                     ("use_multipath_for_image_xfer", True),
@@ -114,7 +122,7 @@
                 ]
             )
 
-        create_storpool_conf(StorPoolConfItems.from_config(config))
+        create_storpool_conf(StorPoolConfItems.from_config(charm_config))
 
         self._stored.is_started = True
 
@@ -138,19 +146,26 @@
         if config["protocol"] == "block":
             return "'protocol' value 'block' not yet supported"
 
-        if not (0 < config["sp-api-http-port"] < 65536):
+        if not 0 < config["sp-api-http-port"] < 65536:
             return (
                 f"""'sp-api-http-port' ('{config["sp-api-http-port"]}')"""
                 "is not a valid port (0-65535)"
             )
 
+        return None
+
 
 @charm_class
 class CinderStorPoolCharm(CinderCharmBase):
+    """
+    Actual class for the StorPool charm
+    """
+
     release = "yoga"
 
 
 def create_storpool_conf(sp_conf_items: StorPoolConfItems):
+    """Generate a storpool.conf with the provided options"""
     pathlib.Path("/etc/storpool.conf").write_text(
         "# Do not edit; this file is generated by the cinder-storpool charm.\n"
         + sp_conf_items.to_ini_key_value_pairs(),