diff --git a/advlabdb/actions.py b/advlabdb/actions.py
index 8ec8a56..62bbbb0 100644
--- a/advlabdb/actions.py
+++ b/advlabdb/actions.py
@@ -25,7 +25,7 @@ def backup(backup_prefix):
     now = datetime.now().strftime("%d_%m_%Y_%H_%M_%S")
     dest = db_bk_dir / f"{backup_prefix}_{now}.sqlite"
 
-    status = subprocess.run(["sqlite3", db_path, f".backup {dest}"]).returncode
+    status = subprocess.run(["sqlite3", db_path, f".backup {dest}"], check=False).returncode
     if status == 0:
         flash(f"Created a database backup at the path {dest}", "success")
     else:
diff --git a/advlabdb/adminModelViews.py b/advlabdb/adminModelViews.py
index 43617ac..a727a3e 100644
--- a/advlabdb/adminModelViews.py
+++ b/advlabdb/adminModelViews.py
@@ -311,9 +311,8 @@ class UserView(SecureAdminModelView):
                 f"{model.email} registered with role(s): {', '.join(role.name for role in model.roles)}.",
                 category="success",
             )
-        else:
-            if model == current_user:
-                flash(f"Active semester is {model.active_semester}.", "warning")
+        elif model == current_user:
+            flash(f"Active semester is {model.active_semester}.", "warning")
 
 
 class SemesterView(SecureAdminModelView):
@@ -418,10 +417,9 @@ class SemesterView(SecureAdminModelView):
             else:
                 current_user.active_semester = model
                 flash(f"Active semester changed to the new semester {model}!", "warning")
-        else:
-            if model.done:
-                next_semester = db.session.get(Semester, model.id + 1)
-                model.set_done(next_semester)
+        elif model.done:
+            next_semester = db.session.get(Semester, model.id + 1)
+            model.set_done(next_semester)
 
 
 def programQueryFactory():
diff --git a/advlabdb/database_import.py b/advlabdb/database_import.py
index 6b27b16..7c34d10 100644
--- a/advlabdb/database_import.py
+++ b/advlabdb/database_import.py
@@ -25,7 +25,7 @@ from .models import (
 
 
 def is_null(entry):
-    return entry == "NULL" or entry == ""
+    return entry in {"NULL", ""}
 
 
 def nullable(entry):
diff --git a/advlabdb/models.py b/advlabdb/models.py
index fd200e7..820cf71 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -457,13 +457,12 @@ class Appointment(db.Model):
         if assistant is not None:
             if assistant not in semesterExperimentAssistants:
                 raise DatabaseException(f"{assistant} is not responsible for {semesterExperiment}!")
+        elif len(semesterExperimentAssistants) == 1:
+            assistant = semesterExperimentAssistants[0]
         else:
-            if len(semesterExperimentAssistants) == 1:
-                assistant = semesterExperimentAssistants[0]
-            else:
-                raise DatabaseException(
-                    f"Experiment {semesterExperiment} has more than one assistant. You have to assign one of these assistants: {semesterExperimentAssistants}"
-                )
+            raise DatabaseException(
+                f"Experiment {semesterExperiment} has more than one assistant. You have to assign one of these assistants: {semesterExperimentAssistants}"
+            )
 
         return assistant
 
diff --git a/cli/test/generate_test_db/main.py b/cli/test/generate_test_db/main.py
index 8f2e781..d4049d2 100644
--- a/cli/test/generate_test_db/main.py
+++ b/cli/test/generate_test_db/main.py
@@ -1,6 +1,6 @@
 from datetime import date
 from math import ceil
-from random import randint, random
+from random import randint
 
 import click
 from flask_security.utils import hash_password
@@ -97,7 +97,7 @@ def _generate_test_db():
             part = ss_parts[ind % len(ss_parts)]
             add_part_student(student, part)
 
-            if random() < 0.9:  # nosec: B311
+            if ind % 10 < 9:
                 # Transfer to the next part in the second semester
                 if part == bs_1_ss_part:
                     add_part_student(student, bs_2_ws_part)
diff --git a/manage.py b/manage.py
index 3d9a6d8..10e86df 100755
--- a/manage.py
+++ b/manage.py
@@ -13,7 +13,7 @@ from cli.test.generate_test_db.main import _generate_test_db
 class Manage:
     @staticmethod
     def run(command: str, **kwargs):
-        return subprocess.run(command, shell=True, **kwargs)  # nosec B602
+        return subprocess.run(command, shell=True, check=False, **kwargs)  # nosec B602
 
     @staticmethod
     def box(message: str):
diff --git a/pyproject.toml b/pyproject.toml
index eeb53d8..f0d954d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -27,8 +27,28 @@ requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"
 
 [tool.ruff]
-select = ["E", "W", "F", "I", "UP", "YTT", "S", "B", "C4", "ICN", "PIE", "Q", "RET", "SIM", "TID", "PTH"]
-ignore = ["E5", "S3", "S6", "RET504"]
+select = [
+  "E",
+  "W",
+  "F",
+  "I",
+  "UP",
+  "YTT",
+  "S",
+  "B",
+  "C4",
+  "ICN",
+  "PIE",
+  "Q",
+  "RET",
+  "SIM",
+  "TID",
+  "PTH",
+  "ERA",
+  "PL",
+  "NPY",
+]
+ignore = ["E5", "S3", "S6", "RET504", "PLR0912", "PLR0915", "PLW2901", "PLR2004"]
 line-length = 120
 
 [tool.ruff.per-file-ignores]