Use frozensets for some membership tests

src/django_upgrade/fixers/mail_api_kwargs.py

@@ -79,7 +79,7 @@ def __init__(
     ),
 }
 
-MESSAGE_MODULE_NAMES = {"EmailMessage", "EmailMultiAlternatives"}
+MESSAGE_MODULE_NAMES = frozenset({"EmailMessage", "EmailMultiAlternatives"})
 
 
 @fixer.register(ast.Call)

src/django_upgrade/fixers/model_field_choices.py

@@ -63,11 +63,13 @@ def defined_enumeration_types(module: ast.Module, up_to_line: int) -> set[str]:
     }
 
 
-DJANGO_CHOICES_TYPES = {
-    "TextChoices",
-    "IntegerChoices",
-    "Choices",
-}
+DJANGO_CHOICES_TYPES = frozenset(
+    {
+        "TextChoices",
+        "IntegerChoices",
+        "Choices",
+    }
+)
 
 
 def _is_django_choices_type(

src/django_upgrade/fixers/on_delete.py

@@ -21,6 +21,8 @@
     min_version=(1, 9),
 )
 
+RELATION_FIELD_NAMES = frozenset({"ForeignKey", "OneToOneField"})
+
 
 @fixer.register(ast.ImportFrom)
 def visit_ImportFrom(
@@ -31,7 +33,7 @@ def visit_ImportFrom(
     if (
         node.module == "django.db.models"
         and is_rewritable_import_from(node)
-        and any(alias.name in {"ForeignKey", "OneToOneField"} for alias in node.names)
+        and any(alias.name in RELATION_FIELD_NAMES for alias in node.names)
     ):
         yield (
             ast_start_offset(node),
@@ -70,14 +72,14 @@ def visit_Call(
         (
             (
                 isinstance(node.func, ast.Attribute)
-                and node.func.attr in {"ForeignKey", "OneToOneField"}
+                and node.func.attr in RELATION_FIELD_NAMES
                 and (models_imported := "models" in state.from_imports["django.db"])
                 and isinstance(node.func.value, ast.Name)
                 and node.func.value.id == "models"
             )
             or (
                 isinstance(node.func, ast.Name)
-                and node.func.id in {"ForeignKey", "OneToOneField"}
+                and node.func.id in RELATION_FIELD_NAMES
                 and node.func.id in state.from_imports["django.db.models"]
                 and (models_imported := False) is False  # force walrus
             )

src/django_upgrade/fixers/postgres_float_range_field.py

@@ -20,12 +20,14 @@
     min_version=(2, 2),
 )
 
-MODULES = {
-    "django.contrib.postgres.fields",
-    "django.contrib.postgres.fields.ranges",
-    "django.contrib.postgres.forms",
-    "django.contrib.postgres.forms.ranges",
-}
+MODULES = frozenset(
+    {
+        "django.contrib.postgres.fields",
+        "django.contrib.postgres.fields.ranges",
+        "django.contrib.postgres.forms",
+        "django.contrib.postgres.forms.ranges",
+    }
+)
 NAME_MAP = {
     "FloatRangeField": "DecimalRangeField",
 }

src/django_upgrade/fixers/request_headers.py

@@ -20,6 +20,8 @@
     min_version=(2, 2),
 )
 
+SPECIAL_HEADERS = frozenset({"CONTENT_LENGTH", "CONTENT_TYPE"})
+
 
 @fixer.register(ast.Subscript)
 def visit_Subscript(
@@ -109,7 +111,7 @@ def get_header_name(meta_name: str) -> str | None:
     http_prefix = "HTTP_"
     if meta_name.startswith(http_prefix):
         name = meta_name[len(http_prefix) :]
-    elif meta_name in {"CONTENT_LENGTH", "CONTENT_TYPE"}:
+    elif meta_name in SPECIAL_HEADERS:
         name = meta_name
     else:
         return None