Use keyword-only arguments in public API (adap#1338)

* Use keyword-only arguments in public API
* Update changelog and upgrade guide

doc/source/changelog.md

@@ -55,6 +55,10 @@ We thank all contributors who made Flower 1.0 possible (in reverse [GitHub Contr
 
 ### Incompatible changes
 
+- **All arguments must be passed as keyword arguments** ([#1338](https://github.com/adap/flower/pull/1338))
+
+  Pass all arguments as keyword arguments, positional arguments are not longer supported. Code that uses positional arguments (e.g., ``start_client("127.0.0.1:8080", FlowerClient())``) must add the keyword for each positional argument (e.g., ``start_client(server_address="127.0.0.1:8080", client=FlowerClient())``).
+
 - **Introduce configuration object** `ServerConfig` **in** `start_server` **and** `start_simulation` ([#1317](https://github.com/adap/flower/pull/1317))
 
   Instead of a config dictionary `{"num_rounds": 3, "round_timeout": 600.0}`, `start_server` and `start_simulation` now expect a configuration object of type `flwr.server.ServerConfig`. `ServerConfig` takes the same arguments that as the previous config dict, but it makes writing type-safe code easier and the default parameters values more transparent.

doc/source/upgrade-to-flower-1.0.rst

@@ -23,6 +23,14 @@ Required changes
 
 A few breaking changes require small manual updates:
 
+General
+~~~~~~~
+
+Pass all arguments as keyword arguments (not as positional arguments). Here's an example:
+
+- Flower 0.19 (positional arguments): ``start_client("127.0.0.1:8080", FlowerClient())``
+- Flower 1.0 (keyword arguments): ``start_client(server_address="127.0.0.1:8080", client=FlowerClient())``
+
 Client
 ~~~~~~
 

src/py/flwr/client/app.py

@@ -79,6 +79,7 @@
 
 
 def start_client(
+    *,
     server_address: str,
     client: Client,
     grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
@@ -157,6 +158,7 @@ class `flwr.client.Client`.
 
 
 def start_numpy_client(
+    *,
     server_address: str,
     client: NumPyClient,
     grpc_max_message_length: int = GRPC_MAX_MESSAGE_LENGTH,
@@ -166,26 +168,22 @@ def start_numpy_client(
 
     Parameters
     ----------
-        server_address: str. The IPv6 address of the server. If the Flower
-            server runs on the same machine on port 8080, then `server_address`
-            would be `"[::]:8080"`.
-        client: flwr.client.NumPyClient. An implementation of the abstract base
-            class `flwr.client.NumPyClient`.
-        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 server. The default should be sufficient for most models.
-            Users who train very large models might need to increase this
-            value. Note that the Flower server needs to be started with the
-            same value (see `flwr.server.start_server`), otherwise it will not
-            know about the increased limit and block larger messages.
-        root_certificates: bytes (default: None)
-            The PEM-encoded root certificates a byte string. If provided, a secure
-            connection using the certificates will be established to a
-            SSL-enabled Flower server.
-
-    Returns
-    -------
-        None
+    server_address : str
+        The IPv6 address of the server. If the Flower server runs on the same
+        machine on port 8080, then `server_address` would be `"[::]:8080"`.
+    client : flwr.client.NumPyClient
+        An implementation of the abstract base class `flwr.client.NumPyClient`.
+    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 server. The default should be sufficient for most models.
+        Users who train very large models might need to increase this
+        value. Note that the Flower server needs to be started with the
+        same value (see `flwr.server.start_server`), otherwise it will not
+        know about the increased limit and block larger messages.
+    root_certificates : bytes (default: None)
+        The PEM-encoded root certificates a byte string. If provided, a secure
+        connection using the certificates will be established to a
+        SSL-enabled Flower server.
 
     Examples
     --------

src/py/flwr/server/app.py

@@ -43,6 +43,7 @@ class ServerConfig:
 
 
 def start_server(  # pylint: disable=too-many-arguments
+    *,
     server_address: str = DEFAULT_SERVER_ADDRESS,
     server: Optional[Server] = None,
     config: Optional[ServerConfig] = None,

src/py/flwr/server/server.py

@@ -56,7 +56,7 @@ class Server:
     """Flower server."""
 
     def __init__(
-        self, client_manager: ClientManager, strategy: Optional[Strategy] = None
+        self, *, client_manager: ClientManager, strategy: Optional[Strategy] = None
     ) -> None:
         self._client_manager: ClientManager = client_manager
         self.parameters: Parameters = Parameters(

src/py/flwr/server/strategy/fault_tolerant_fedavg.py

@@ -41,6 +41,7 @@ class FaultTolerantFedAvg(FedAvg):
     # pylint: disable=too-many-arguments,too-many-instance-attributes
     def __init__(
         self,
+        *,
         fraction_fit: float = 1.0,
         fraction_evaluate: float = 1.0,
         min_fit_clients: int = 1,

src/py/flwr/server/strategy/fedavg.py

@@ -54,6 +54,7 @@ class FedAvg(Strategy):
     # pylint: disable=too-many-arguments,too-many-instance-attributes
     def __init__(
         self,
+        *,
         fraction_fit: float = 1.0,
         fraction_evaluate: float = 1.0,
         min_fit_clients: int = 2,

src/py/flwr/server/strategy/fedavg_android.py

@@ -46,6 +46,7 @@ class FedAvgAndroid(Strategy):
     # pylint: disable=too-many-arguments,too-many-instance-attributes
     def __init__(
         self,
+        *,
         fraction_fit: float = 1.0,
         fraction_evaluate: float = 1.0,
         min_fit_clients: int = 2,

src/py/flwr/server/strategy/qfedavg.py

@@ -50,6 +50,7 @@ class QFedAvg(FedAvg):
     # pylint: disable=too-many-arguments,too-many-instance-attributes
     def __init__(
         self,
+        *,
         q_param: float = 0.2,
         qffl_learning_rate: float = 0.1,
         fraction_fit: float = 1.0,