diff --git a/luigi/execution_summary.py b/luigi/execution_summary.py
index a430fd61c8..e818a1ed14 100644
--- a/luigi/execution_summary.py
+++ b/luigi/execution_summary.py
@@ -94,14 +94,14 @@ def _partition_tasks(worker):
     Still_pending_not_ext is only used to get upstream_failure, upstream_missing_dependency and run_by_other_worker
     """
     task_history = worker._add_task_history
-    pending_tasks = {task for(task, status, ext) in task_history if status == 'PENDING'}
+    pending_tasks = {task for (task, status, ext) in task_history if status == 'PENDING'}
     set_tasks = {}
     set_tasks["completed"] = {task for (task, status, ext) in task_history if status == 'DONE' and task in pending_tasks}
     set_tasks["already_done"] = {task for (task, status, ext) in task_history
                                  if status == 'DONE' and task not in pending_tasks and task not in set_tasks["completed"]}
     set_tasks["ever_failed"] = {task for (task, status, ext) in task_history if status == 'FAILED'}
     set_tasks["failed"] = set_tasks["ever_failed"] - set_tasks["completed"]
-    set_tasks["scheduling_error"] = {task for(task, status, ext) in task_history if status == 'UNKNOWN'}
+    set_tasks["scheduling_error"] = {task for (task, status, ext) in task_history if status == 'UNKNOWN'}
     set_tasks["still_pending_ext"] = {task for (task, status, ext) in task_history
                                       if status == 'PENDING' and task not in set_tasks["ever_failed"] and task not in set_tasks["completed"] and not ext}
     set_tasks["still_pending_not_ext"] = {task for (task, status, ext) in task_history
diff --git a/luigi/interface.py b/luigi/interface.py
index 5fd33b947e..6a2b336866 100644
--- a/luigi/interface.py
+++ b/luigi/interface.py
@@ -146,7 +146,7 @@ def _schedule_and_run(tasks, worker_scheduler_factory=None, override_defaults=No
 
     kill_signal = signal.SIGUSR1 if env_params.take_lock else None
     if (not env_params.no_lock and
-            not(lock.acquire_for(env_params.lock_pid_dir, env_params.lock_size, kill_signal))):
+            not (lock.acquire_for(env_params.lock_pid_dir, env_params.lock_size, kill_signal))):
         raise PidLockAlreadyTakenExit()
 
     if env_params.local_scheduler:
diff --git a/luigi/tools/deps_tree.py b/luigi/tools/deps_tree.py
index 9f207341b7..77e49e2229 100755
--- a/luigi/tools/deps_tree.py
+++ b/luigi/tools/deps_tree.py
@@ -50,7 +50,7 @@ def print_tree(task, indent='', last=True):
     name = task.__class__.__name__
     params = task.to_str_params(only_significant=True)
     result = '\n' + indent
-    if(last):
+    if (last):
         result += '└─--'
         indent += '    '
     else:
diff --git a/test/task_test.py b/test/task_test.py
index c3f569423b..cd95b88b87 100644
--- a/test/task_test.py
+++ b/test/task_test.py
@@ -78,7 +78,7 @@ def test_task_missing_necessary_param(self):
 
     def test_external_tasks_loadable(self):
         task = load_task("luigi", "ExternalTask", {})
-        assert(isinstance(task, luigi.ExternalTask))
+        self.assertTrue(isinstance(task, luigi.ExternalTask))
 
     def test_getpaths(self):
         class RequiredTask(luigi.Task):