chg: entities.update optional label and data params, update readme

- chg: label or data (or both/neither) are allowed for entities.update
- add: readme section on default identifiers

README.md

@@ -64,6 +64,18 @@ The `Client` is not specific to a project, but a default `project_id` can be set
 - An init argument: `Client(project_id=1)`.
 - A property on the client: `client.project_id = 1`.
 
+*Default Identifiers*
+
+For each endpoint, a default can be set for key identifiers, so these identifiers are optional in most methods. When the identifier is required, validation ensures that either a default value is set, or a value is specified. E.g.
+
+```python
+client.projects.default_project_id = 1
+client.forms.default_form_id = "my_form"
+client.submissions.default_form_id = "my_form"
+client.entities.default_entity_list_name = "my_list"
+client.entities.default_project_id = 1
+```
+
 ### Session cache file
 
 The session cache file uses the TOML format. The default file name is `.pyodk_cache.toml`, and the default location is the user home directory. The file name and location can be customised by setting the environment variable `PYODK_CACHE_FILE` to some other file path, or by passing the path at init with `Client(config_path="my_cache.toml")`. This file should not be pre-created as it is used to store a session token after login.

pyodk/_endpoints/entities.py

@@ -146,20 +146,20 @@ def create(
 
     def update(
         self,
-        label: str,
-        data: dict,
         uuid: str,
-        force: bool | None = None,
-        base_version: int | None = None,
         entity_list_name: str | None = None,
         project_id: int | None = None,
+        label: str | None = None,
+        data: dict | None = None,
+        force: bool | None = None,
+        base_version: int | None = None,
     ) -> Entity:
         """
         Update an Entity.
 
+        :param uuid: The unique identifier for the Entity.
         :param label: Label of the Entity.
         :param data: Data to store for the Entity.
-        :param uuid: The unique identifier for the Entity.
         :param force: If True, update an Entity regardless of its current state. If
           `base_version` is not specified, then `force` must be True.
         :param base_version: The expected current version of the Entity on the server. If
@@ -181,10 +181,11 @@ def update(
                 params["baseVersion"] = pv.validate_int(base_version, key="base_version")
             if len([i for i in (force, base_version) if i is not None]) != 1:
                 raise PyODKError("Must specify one of 'force' or 'base_version'.")  # noqa: TRY301
-            req_data = {
-                "label": pv.validate_str(label, key="label"),
-                "data": pv.validate_dict(data, key="data"),
-            }
+            req_data = {}
+            if label is not None:
+                req_data["label"] = pv.validate_str(label, key="label")
+            if data is not None:
+                req_data["data"] = pv.validate_dict(data, key="data")
         except PyODKError as err:
             log.error(err, exc_info=True)
             raise