Fix aio-libs#8253

aiohttp/client.py

@@ -243,6 +243,14 @@ def __init__(
         max_field_size: int = 8190,
         fallback_charset_resolver: _CharsetResolver = lambda r, b: "utf-8",
     ) -> None:
+        if timeout is sentinel or timeout is None:
+            timeout = DEFAULT_TIMEOUT
+        if not isinstance(timeout, ClientTimeout):
+            raise ValueError(
+                f"timeout parameter cannot be of {type(timeout)} type, "
+                "please use 'timeout=ClientTimeout(...)'",
+            )
+        self._timeout = timeout
         if base_url is None or isinstance(base_url, URL):
             self._base_url: Optional[URL] = base_url
         else:
@@ -281,14 +289,7 @@ def __init__(
         self._default_auth = auth
         self._version = version
         self._json_serialize = json_serialize
-        if timeout is sentinel or timeout is None:
-            timeout = DEFAULT_TIMEOUT
-        if not isinstance(timeout, ClientTimeout):
-            raise ValueError(
-                f"timeout parameter cannot be of {type(timeout)} type, "
-                "please use 'timeout=ClientTimeout(...)'",
-            )
-        self._timeout = timeout
+
         self._raise_for_status = raise_for_status
         self._auto_decompress = auto_decompress
         self._trust_env = trust_env
@@ -325,6 +326,10 @@ def __init_subclass__(cls: Type["ClientSession"]) -> None:
         )
 
     def __del__(self, _warnings: Any = warnings) -> None:
+        if not hasattr(self, 'closed'):
+            # has not been initialized, nothing to do
+            return
+
         if not self.closed:
             _warnings.warn(
                 f"Unclosed client session {self!r}",

tests/test_client_session.py

@@ -841,3 +841,13 @@ async def test_build_url_returns_expected_url(
 ) -> None:
     session = await create_session(base_url)
     assert session._build_url(url) == expected_url
+
+
+async def test_instantiation_with_invalid_timeout_value(loop):
+    loop.set_debug(False)
+    logs = []
+    loop.set_exception_handler(lambda loop, ctx: logs.append(ctx))
+    with pytest.raises(ValueError, match="timeout parameter cannot be .*"):
+        ClientSession(timeout=1)
+    # should not have "Unclosed client session" warning
+    assert not logs