diff --git a/fastapi/applications.py b/fastapi/applications.py
index 95f6e26ee..27a72fe31 100644
--- a/fastapi/applications.py
+++ b/fastapi/applications.py
@@ -117,11 +117,8 @@ class FastAPI(Starlette):
 
     def setup(self) -> None:
         if self.openapi_url:
-            server_urls = set()
-            for server_data in self.servers:
-                url = server_data.get("url")
-                if url:
-                    server_urls.add(url)
+            urls = (server_data.get("url") for server_data in self.servers)
+            server_urls = {url for url in urls if url}
 
             async def openapi(req: Request) -> JSONResponse:
                 root_path = req.scope.get("root_path", "").rstrip("/")
diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py
index 2c70b2c10..f35b2d0ba 100644
--- a/fastapi/dependencies/utils.py
+++ b/fastapi/dependencies/utils.py
@@ -746,7 +746,7 @@ def get_body_field(*, dependant: Dependant, name: str) -> Optional[ModelField]:
     first_param = flat_dependant.body_params[0]
     field_info = get_field_info(first_param)
     embed = getattr(field_info, "embed", None)
-    body_param_names_set = set([param.name for param in flat_dependant.body_params])
+    body_param_names_set = {param.name for param in flat_dependant.body_params}
     if len(body_param_names_set) == 1 and not embed:
         return get_schema_compatible_field(field=first_param)
     # If one field requires to embed, all have to be embedded
diff --git a/fastapi/encoders.py b/fastapi/encoders.py
index bf85fff81..003dd58ce 100644
--- a/fastapi/encoders.py
+++ b/fastapi/encoders.py
@@ -1,3 +1,4 @@
+from collections import defaultdict
 from enum import Enum
 from pathlib import PurePath
 from types import GeneratorType
@@ -15,9 +16,9 @@ DictIntStrAny = Dict[Union[int, str], Any]
 def generate_encoders_by_class_tuples(
     type_encoder_map: Dict[Any, Callable]
 ) -> Dict[Callable, Tuple]:
-    encoders_by_classes: Dict[Callable, List] = {}
+    encoders_by_classes: Dict[Callable, List] = defaultdict(list)
     for type_, encoder in type_encoder_map.items():
-        encoders_by_classes.setdefault(encoder, []).append(type_)
+        encoders_by_classes[encoder].append(type_)
     encoders_by_class_tuples: Dict[Callable, Tuple] = {}
     for encoder, classes in encoders_by_classes.items():
         encoders_by_class_tuples[encoder] = tuple(classes)
diff --git a/fastapi/openapi/constants.py b/fastapi/openapi/constants.py
index 000011a1f..3e69e5524 100644
--- a/fastapi/openapi/constants.py
+++ b/fastapi/openapi/constants.py
@@ -1,3 +1,3 @@
-METHODS_WITH_BODY = set(("GET", "HEAD", "POST", "PUT", "DELETE", "PATCH"))
-STATUS_CODES_WITH_NO_BODY = set((100, 101, 102, 103, 204, 304))
+METHODS_WITH_BODY = {"GET", "HEAD", "POST", "PUT", "DELETE", "PATCH"}
+STATUS_CODES_WITH_NO_BODY = {100, 101, 102, 103, 204, 304}
 REF_PREFIX = "#/components/schemas/"
diff --git a/fastapi/security/http.py b/fastapi/security/http.py
index 80eec005d..3258bd058 100644
--- a/fastapi/security/http.py
+++ b/fastapi/security/http.py
@@ -86,7 +86,7 @@ class HTTPBasic(HTTPBase):
         except (ValueError, UnicodeDecodeError, binascii.Error):
             raise invalid_user_credentials_exc
         username, separator, password = data.partition(":")
-        if not (separator):
+        if not separator:
             raise invalid_user_credentials_exc
         return HTTPBasicCredentials(username=username, password=password)