We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Improve docstring for `start_server`


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `src/py/flwr/server/app.py`
Content:
```
1 # Copyright 2020 Adap GmbH. All Rights Reserved.
2 #
3 # Licensed under the Apache License, Version 2.0 (the "License");
4 # you may not use this file except in compliance with the License.
5 # You may obtain a copy of the License at
6 #
7 #     http://www.apache.org/licenses/LICENSE-2.0
8 #
9 # Unless required by applicable law or agreed to in writing, software
10 # distributed under the License is distributed on an "AS IS" BASIS,
11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 # See the License for the specific language governing permissions and
13 # limitations under the License.
14 # ==============================================================================
15 """Flower server app."""
16 
17 
18 from logging import INFO
19 from typing import Dict, Optional
20 
21 from flwr.common import GRPC_MAX_MESSAGE_LENGTH
22 from flwr.common.logger import log
23 from flwr.server.client_manager import SimpleClientManager
24 from flwr.server.grpc_server.grpc_server import start_insecure_grpc_server
25 from flwr.server.server import Server
26 from flwr.server.strategy import FedAvg, Strategy
27 
28 DEFAULT_SERVER_ADDRESS = "[::]:8080"
29 
30 
31 def start_server(
32     server_address: str = DEFAULT_SERVER_ADDRESS,
33     server: Optional[Server] = None,
34     config: Optional[Dict[str, int]] = None,
35     strategy: Optional[Strategy] = None,
36     grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
37 ) -> None:
38     """Start a Flower server using the gRPC transport layer."""
39 
40     # Create server instance if none was given
41     if server is None:
42         client_manager = SimpleClientManager()
43         if strategy is None:
44             strategy = FedAvg()
45         server = Server(client_manager=client_manager, strategy=strategy)
46 
47     # Set default config values
48     if config is None:
49         config = {}
50     if "num_rounds" not in config:
51         config["num_rounds"] = 1
52 
53     # Start gRPC server
54     grpc_server = start_insecure_grpc_server(
55         client_manager=server.client_manager(),
56         server_address=server_address,
57         max_message_length=grpc_max_message_length,
58     )
59     log(INFO, "Flower server running (insecure, %s rounds)", config["num_rounds"])
60 
61     # Fit model
62     hist = server.fit(num_rounds=config["num_rounds"])
63     log(INFO, "app_fit: losses_distributed %s", str(hist.losses_distributed))
64     log(INFO, "app_fit: accuracies_distributed %s", str(hist.accuracies_distributed))
65     log(INFO, "app_fit: losses_centralized %s", str(hist.losses_centralized))
66     log(INFO, "app_fit: accuracies_centralized %s", str(hist.accuracies_centralized))
67 
68     # Temporary workaround to force distributed evaluation
69     server.strategy.eval_fn = None  # type: ignore
70 
71     # Evaluate the final trained model
72     res = server.evaluate(rnd=-1)
73     if res is not None:
74         loss, (results, failures) = res
75         log(INFO, "app_evaluate: federated loss: %s", str(loss))
76         log(
77             INFO,
78             "app_evaluate: results %s",
79             str([(res[0].cid, res[1]) for res in results]),
80         )
81         log(INFO, "app_evaluate: failures %s", str(failures))
82     else:
83         log(INFO, "app_evaluate: no evaluation result")
84 
85     # Stop the gRPC server
86     grpc_server.stop(1)
87
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/src/py/flwr/server/app.py b/src/py/flwr/server/app.py
--- a/src/py/flwr/server/app.py
+++ b/src/py/flwr/server/app.py
@@ -35,7 +35,33 @@
     strategy: Optional[Strategy] = None,
     grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
 ) -> None:
-    """Start a Flower server using the gRPC transport layer."""
+    """Start a Flower server using the gRPC transport layer.
+
+    Arguments:
+        server_address: Optional[str] (default: `"[::]:8080"`). The IPv6
+            address of the server.
+        server: Optional[flwr.server.Server] (default: None). An implementation
+            of the abstract base class `flwr.server.Server`. If no instance is
+            provided, then `start_server` will create one.
+        config: Optional[Dict[str, int]] (default: None). The only currently
+            supported values is `num_rounds`, so a full configuration object
+            instructing the server to perform three rounds of federated
+            learning looks like the following: `{"num_rounds": 3}`.
+        strategy: Optional[flwr.server.Strategy] (default: None). An
+            implementation of the abstract base class `flwr.server.Strategy`.
+            If no strategy is provided, then `start_server` will use
+            `flwr.server.strategy.FedAvg`.
+        grpc_max_message_length: int (default: 536_870_912, this equals 512MB).
+            The maximum length of gRPC messages that can be exchanged with the
+            Flower clients. The default should be sufficient for most models.
+            Users who train very large models might need to increase this
+            value. Note that the Flower clients needs to started with the same
+            value (see `flwr.client.start_client`), otherwise clients will not
+            know about the increased limit and block larger messages.
+
+    Returns:
+        None.
+    """
 
     # Create server instance if none was given
     if server is None:

{"golden_diff": "diff --git a/src/py/flwr/server/app.py b/src/py/flwr/server/app.py\n--- a/src/py/flwr/server/app.py\n+++ b/src/py/flwr/server/app.py\n@@ -35,7 +35,33 @@\n     strategy: Optional[Strategy] = None,\n     grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,\n ) -> None:\n-    \"\"\"Start a Flower server using the gRPC transport layer.\"\"\"\n+    \"\"\"Start a Flower server using the gRPC transport layer.\n+\n+    Arguments:\n+        server_address: Optional[str] (default: `\"[::]:8080\"`). The IPv6\n+            address of the server.\n+        server: Optional[flwr.server.Server] (default: None). An implementation\n+            of the abstract base class `flwr.server.Server`. If no instance is\n+            provided, then `start_server` will create one.\n+        config: Optional[Dict[str, int]] (default: None). The only currently\n+            supported values is `num_rounds`, so a full configuration object\n+            instructing the server to perform three rounds of federated\n+            learning looks like the following: `{\"num_rounds\": 3}`.\n+        strategy: Optional[flwr.server.Strategy] (default: None). An\n+            implementation of the abstract base class `flwr.server.Strategy`.\n+            If no strategy is provided, then `start_server` will use\n+            `flwr.server.strategy.FedAvg`.\n+        grpc_max_message_length: int (default: 536_870_912, this equals 512MB).\n+            The maximum length of gRPC messages that can be exchanged with the\n+            Flower clients. The default should be sufficient for most models.\n+            Users who train very large models might need to increase this\n+            value. Note that the Flower clients needs to started with the same\n+            value (see `flwr.client.start_client`), otherwise clients will not\n+            know about the increased limit and block larger messages.\n+\n+    Returns:\n+        None.\n+    \"\"\"\n \n     # Create server instance if none was given\n     if server is None:\n", "issue": "Improve docstring for `start_server`\n\n", "before_files": [{"content": "# Copyright 2020 Adap GmbH. All Rights Reserved.\n#\n# Licensed under the Apache License, Version 2.0 (the \"License\");\n# you may not use this file except in compliance with the License.\n# You may obtain a copy of the License at\n#\n#     http://www.apache.org/licenses/LICENSE-2.0\n#\n# Unless required by applicable law or agreed to in writing, software\n# distributed under the License is distributed on an \"AS IS\" BASIS,\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n# See the License for the specific language governing permissions and\n# limitations under the License.\n# ==============================================================================\n\"\"\"Flower server app.\"\"\"\n\n\nfrom logging import INFO\nfrom typing import Dict, Optional\n\nfrom flwr.common import GRPC_MAX_MESSAGE_LENGTH\nfrom flwr.common.logger import log\nfrom flwr.server.client_manager import SimpleClientManager\nfrom flwr.server.grpc_server.grpc_server import start_insecure_grpc_server\nfrom flwr.server.server import Server\nfrom flwr.server.strategy import FedAvg, Strategy\n\nDEFAULT_SERVER_ADDRESS = \"[::]:8080\"\n\n\ndef start_server(\n    server_address: str = DEFAULT_SERVER_ADDRESS,\n    server: Optional[Server] = None,\n    config: Optional[Dict[str, int]] = None,\n    strategy: Optional[Strategy] = None,\n    grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,\n) -> None:\n    \"\"\"Start a Flower server using the gRPC transport layer.\"\"\"\n\n    # Create server instance if none was given\n    if server is None:\n        client_manager = SimpleClientManager()\n        if strategy is None:\n            strategy = FedAvg()\n        server = Server(client_manager=client_manager, strategy=strategy)\n\n    # Set default config values\n    if config is None:\n        config = {}\n    if \"num_rounds\" not in config:\n        config[\"num_rounds\"] = 1\n\n    # Start gRPC server\n    grpc_server = start_insecure_grpc_server(\n        client_manager=server.client_manager(),\n        server_address=server_address,\n        max_message_length=grpc_max_message_length,\n    )\n    log(INFO, \"Flower server running (insecure, %s rounds)\", config[\"num_rounds\"])\n\n    # Fit model\n    hist = server.fit(num_rounds=config[\"num_rounds\"])\n    log(INFO, \"app_fit: losses_distributed %s\", str(hist.losses_distributed))\n    log(INFO, \"app_fit: accuracies_distributed %s\", str(hist.accuracies_distributed))\n    log(INFO, \"app_fit: losses_centralized %s\", str(hist.losses_centralized))\n    log(INFO, \"app_fit: accuracies_centralized %s\", str(hist.accuracies_centralized))\n\n    # Temporary workaround to force distributed evaluation\n    server.strategy.eval_fn = None  # type: ignore\n\n    # Evaluate the final trained model\n    res = server.evaluate(rnd=-1)\n    if res is not None:\n        loss, (results, failures) = res\n        log(INFO, \"app_evaluate: federated loss: %s\", str(loss))\n        log(\n            INFO,\n            \"app_evaluate: results %s\",\n            str([(res[0].cid, res[1]) for res in results]),\n        )\n        log(INFO, \"app_evaluate: failures %s\", str(failures))\n    else:\n        log(INFO, \"app_evaluate: no evaluation result\")\n\n    # Stop the gRPC server\n    grpc_server.stop(1)\n", "path": "src/py/flwr/server/app.py"}], "after_files": [{"content": "# Copyright 2020 Adap GmbH. All Rights Reserved.\n#\n# Licensed under the Apache License, Version 2.0 (the \"License\");\n# you may not use this file except in compliance with the License.\n# You may obtain a copy of the License at\n#\n#     http://www.apache.org/licenses/LICENSE-2.0\n#\n# Unless required by applicable law or agreed to in writing, software\n# distributed under the License is distributed on an \"AS IS\" BASIS,\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n# See the License for the specific language governing permissions and\n# limitations under the License.\n# ==============================================================================\n\"\"\"Flower server app.\"\"\"\n\n\nfrom logging import INFO\nfrom typing import Dict, Optional\n\nfrom flwr.common import GRPC_MAX_MESSAGE_LENGTH\nfrom flwr.common.logger import log\nfrom flwr.server.client_manager import SimpleClientManager\nfrom flwr.server.grpc_server.grpc_server import start_insecure_grpc_server\nfrom flwr.server.server import Server\nfrom flwr.server.strategy import FedAvg, Strategy\n\nDEFAULT_SERVER_ADDRESS = \"[::]:8080\"\n\n\ndef start_server(\n    server_address: str = DEFAULT_SERVER_ADDRESS,\n    server: Optional[Server] = None,\n    config: Optional[Dict[str, int]] = None,\n    strategy: Optional[Strategy] = None,\n    grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,\n) -> None:\n    \"\"\"Start a Flower server using the gRPC transport layer.\n\n    Arguments:\n        server_address: Optional[str] (default: `\"[::]:8080\"`). The IPv6\n            address of the server.\n        server: Optional[flwr.server.Server] (default: None). An implementation\n            of the abstract base class `flwr.server.Server`. If no instance is\n            provided, then `start_server` will create one.\n        config: Optional[Dict[str, int]] (default: None). The only currently\n            supported values is `num_rounds`, so a full configuration object\n            instructing the server to perform three rounds of federated\n            learning looks like the following: `{\"num_rounds\": 3}`.\n        strategy: Optional[flwr.server.Strategy] (default: None). An\n            implementation of the abstract base class `flwr.server.Strategy`.\n            If no strategy is provided, then `start_server` will use\n            `flwr.server.strategy.FedAvg`.\n        grpc_max_message_length: int (default: 536_870_912, this equals 512MB).\n            The maximum length of gRPC messages that can be exchanged with the\n            Flower clients. The default should be sufficient for most models.\n            Users who train very large models might need to increase this\n            value. Note that the Flower clients needs to started with the same\n            value (see `flwr.client.start_client`), otherwise clients will not\n            know about the increased limit and block larger messages.\n\n    Returns:\n        None.\n    \"\"\"\n\n    # Create server instance if none was given\n    if server is None:\n        client_manager = SimpleClientManager()\n        if strategy is None:\n            strategy = FedAvg()\n        server = Server(client_manager=client_manager, strategy=strategy)\n\n    # Set default config values\n    if config is None:\n        config = {}\n    if \"num_rounds\" not in config:\n        config[\"num_rounds\"] = 1\n\n    # Start gRPC server\n    grpc_server = start_insecure_grpc_server(\n        client_manager=server.client_manager(),\n        server_address=server_address,\n        max_message_length=grpc_max_message_length,\n    )\n    log(INFO, \"Flower server running (insecure, %s rounds)\", config[\"num_rounds\"])\n\n    # Fit model\n    hist = server.fit(num_rounds=config[\"num_rounds\"])\n    log(INFO, \"app_fit: losses_distributed %s\", str(hist.losses_distributed))\n    log(INFO, \"app_fit: accuracies_distributed %s\", str(hist.accuracies_distributed))\n    log(INFO, \"app_fit: losses_centralized %s\", str(hist.losses_centralized))\n    log(INFO, \"app_fit: accuracies_centralized %s\", str(hist.accuracies_centralized))\n\n    # Temporary workaround to force distributed evaluation\n    server.strategy.eval_fn = None  # type: ignore\n\n    # Evaluate the final trained model\n    res = server.evaluate(rnd=-1)\n    if res is not None:\n        loss, (results, failures) = res\n        log(INFO, \"app_evaluate: federated loss: %s\", str(loss))\n        log(\n            INFO,\n            \"app_evaluate: results %s\",\n            str([(res[0].cid, res[1]) for res in results]),\n        )\n        log(INFO, \"app_evaluate: failures %s\", str(failures))\n    else:\n        log(INFO, \"app_evaluate: no evaluation result\")\n\n    # Stop the gRPC server\n    grpc_server.stop(1)\n", "path": "src/py/flwr/server/app.py"}]}