Use contextlib.nullcontext on Python 3.7+ (#633)

Author: adamchainz

src/django_mysql/compat.py

@@ -0,0 +1,12 @@
+import sys
+
+if sys.version_info >= (3, 7):
+    from contextlib import nullcontext
+else:
+
+    class nullcontext:
+        def __enter__(self):
+            pass
+
+        def __exit__(self, *exc_info):
+            pass

src/django_mysql/models/query.py

@@ -13,6 +13,7 @@
 from django.utils.functional import cached_property
 from django.utils.translation import gettext as _
 
+from django_mysql.compat import nullcontext
 from django_mysql.models.handler import Handler
 from django_mysql.rewrite_query import REWRITE_MARKER
 from django_mysql.status import GlobalStatus
@@ -21,7 +22,6 @@
     WeightedAverageRate,
     format_duration,
     have_program,
-    noop_context,
     settings_to_cmd_args,
 )
 
@@ -305,11 +305,11 @@ def __init__(
         self.queryset = self.sanitize_queryset(queryset)
 
         if atomically:
-            self.maybe_atomic = atomic
+            self.maybe_atomic = atomic(using=self.queryset.db)
         else:
             # Work around for `with` statement not supporting variable number
             # of contexts
-            self.maybe_atomic = noop_context
+            self.maybe_atomic = nullcontext()
 
         self.status_thresholds = status_thresholds
         self.pk_range = pk_range
@@ -334,8 +334,7 @@ def __iter__(self):
             comp = operator.ge  # >=
             direction = -1
         current_pk = first_pk
-        db_alias = self.queryset.db
-        status = GlobalStatus(db_alias)
+        status = GlobalStatus(self.queryset.db)
 
         self.init_progress(direction)
 
@@ -350,7 +349,7 @@ def __iter__(self):
             else:
                 end_pk = max(current_pk, last_pk - 1)
 
-            with StopWatch() as timer, self.maybe_atomic(using=db_alias):
+            with StopWatch() as timer, self.maybe_atomic:
                 if direction == 1:
                     chunk = self.queryset.filter(pk__gte=start_pk, pk__lt=end_pk)
                 else:

src/django_mysql/utils.py

@@ -2,7 +2,6 @@
 import subprocess
 import time
 from collections import defaultdict
-from contextlib import contextmanager
 from queue import Empty, Queue
 from threading import Lock, Thread
 from weakref import WeakKeyDictionary
@@ -74,11 +73,6 @@ def __exit__(self, *args, **kwargs):
         self.total_time = self.end_time - self.start_time
 
 
-@contextmanager
-def noop_context(*args, **kwargs):
-    yield
-
-
 def format_duration(total_seconds):
     hours = total_seconds // 3600
     minutes = (total_seconds % 3600) // 60