python: more linting (#4734)

Ruff has "B" class of lints, including B018 which will nag on useless
expressions, related to #4719. Enable such lints and fix the existing
issues.

Most notably:
- https://beta.ruff.rs/docs/rules/mutable-argument-default/
- https://beta.ruff.rs/docs/rules/assert-false/

---------

Co-authored-by: Alexander Bayandin <alexander@neon.tech>

test_runner/performance/test_gc_feedback.py

@@ -47,7 +47,7 @@ def test_gc_feedback(neon_env_builder: NeonEnvBuilder, zenbenchmark: NeonBenchma
         # without modifying the earlier parts of the table.
         for step in range(n_steps):
             cur.execute(f"INSERT INTO t (step) SELECT {step} FROM generate_series(1, {step_size})")
-            for i in range(n_update_iters):
+            for _ in range(n_update_iters):
                 cur.execute(f"UPDATE t set count=count+1 where step = {step}")
                 cur.execute("vacuum t")
 

test_runner/performance/test_hot_table.py

@@ -33,6 +33,6 @@ def test_hot_table(env: PgCompare):
 
             # Read the table
             with env.record_duration("read"):
-                for i in range(num_reads):
+                for _ in range(num_reads):
                     cur.execute("select * from t;")
                     cur.fetchall()

test_runner/performance/test_layer_map.py

@@ -28,7 +28,7 @@ def test_layer_map(neon_env_builder: NeonEnvBuilder, zenbenchmark):
     endpoint = env.endpoints.create_start("test_layer_map", tenant_id=tenant)
     cur = endpoint.connect().cursor()
     cur.execute("create table t(x integer)")
-    for i in range(n_iters):
+    for _ in range(n_iters):
         cur.execute(f"insert into t values (generate_series(1,{n_records}))")
         time.sleep(1)
 

test_runner/performance/test_parallel_copy_to.py

@@ -6,7 +6,7 @@ from fixtures.neon_fixtures import PgProtocol
 
 
 async def repeat_bytes(buf, repetitions: int):
-    for i in range(repetitions):
+    for _ in range(repetitions):
         yield buf
 
 

test_runner/performance/test_random_writes.py

@@ -77,8 +77,8 @@ def test_random_writes(neon_with_baseline: PgCompare):
 
             # Update random keys
             with env.record_duration("run"):
-                for it in range(n_iterations):
-                    for i in range(n_writes):
+                for _ in range(n_iterations):
+                    for _ in range(n_writes):
                         key = random.randint(1, n_rows)
                         cur.execute(f"update Big set count=count+1 where pk={key}")
                     env.flush()

test_runner/performance/test_seqscans.py

@@ -61,5 +61,5 @@ def test_seqscans(env: PgCompare, scale: int, rows: int, iters: int, workers: in
             cur.execute(f"set max_parallel_workers_per_gather = {workers}")
 
             with env.record_duration("run"):
-                for i in range(iters):
+                for _ in range(iters):
                     cur.execute("select count(*) from t;")