[typing] clean up prefect __init__.py

- Provide more typing details for version info and the local module spec.
- A module `__getattr__` is never called for globals, so the `_slots`
  structure was redundant.
- Minimise what code is run in the `try: ... except:` block.
- For Python 3.10 and up, include more context in the AttributeError.

src/prefect/__init__.py

@@ -2,29 +2,14 @@
 
 # Setup version and path constants
 
+import sys
 from . import _version
 import importlib
 import pathlib
-from typing import TYPE_CHECKING, Any
-
-__version_info__ = _version.get_versions()
-__version__ = __version_info__["version"]
-
-# The absolute path to this module
-__module_path__ = pathlib.Path(__file__).parent
-# The absolute path to the root of the repository, only valid for use during development
-__development_base_path__ = __module_path__.parents[1]
-
-# The absolute path to the built UI within the Python module, used by
-# `prefect server start` to serve a dynamic build of the UI
-__ui_static_subpath__ = __module_path__ / "server" / "ui_build"
-
-# The absolute path to the built UI within the Python module
-__ui_static_path__ = __module_path__ / "server" / "ui"
-
-del _version, pathlib
+from typing import TYPE_CHECKING, Any, Optional, TypedDict, cast
 
 if TYPE_CHECKING:
+    from importlib.machinery import ModuleSpec
     from .main import (
         allow_failure,
         flow,
@@ -45,80 +30,95 @@
         suspend_flow_run,
     )
 
-_slots: dict[str, Any] = {
-    "__version_info__": __version_info__,
-    "__version__": __version__,
-    "__module_path__": __module_path__,
-    "__development_base_path__": __development_base_path__,
-    "__ui_static_subpath__": __ui_static_subpath__,
-    "__ui_static_path__": __ui_static_path__,
-}
+    __spec__: ModuleSpec
+
+    # Versioneer provides version information as dictionaries
+    # with these keys
+    class VersionInfo(TypedDict("_FullRevisionId", {"full-revisionid": str})):
+        version: str
+        dirty: Optional[bool]
+        error: Optional[str]
+        date: Optional[str]
+
+
+__version_info__: "VersionInfo" = cast("VersionInfo", _version.get_versions())
+__version__ = __version_info__["version"]
 
-_public_api: dict[str, tuple[str, str]] = {
+# The absolute path to this module
+__module_path__: pathlib.Path = pathlib.Path(__file__).parent
+# The absolute path to the root of the repository, only valid for use during development
+__development_base_path__: pathlib.Path = __module_path__.parents[1]
+
+# The absolute path to the built UI within the Python module, used by
+# `prefect server start` to serve a dynamic build of the UI
+__ui_static_subpath__: pathlib.Path = __module_path__ / "server" / "ui_build"
+
+# The absolute path to the built UI within the Python module
+__ui_static_path__: pathlib.Path = __module_path__ / "server" / "ui"
+
+del _version, pathlib
+
+_public_api: dict[str, tuple[Optional[str], str]] = {
     "allow_failure": (__spec__.parent, ".main"),
+    "aserve": (__spec__.parent, ".main"),
+    "deploy": (__spec__.parent, ".main"),
     "flow": (__spec__.parent, ".main"),
     "Flow": (__spec__.parent, ".main"),
     "get_client": (__spec__.parent, ".main"),
     "get_run_logger": (__spec__.parent, ".main"),
+    "pause_flow_run": (__spec__.parent, ".main"),
+    "resume_flow_run": (__spec__.parent, ".main"),
+    "serve": (__spec__.parent, ".main"),
     "State": (__spec__.parent, ".main"),
+    "suspend_flow_run": (__spec__.parent, ".main"),
     "tags": (__spec__.parent, ".main"),
     "task": (__spec__.parent, ".main"),
     "Task": (__spec__.parent, ".main"),
     "Transaction": (__spec__.parent, ".main"),
     "unmapped": (__spec__.parent, ".main"),
-    "serve": (__spec__.parent, ".main"),
-    "aserve": (__spec__.parent, ".main"),
-    "deploy": (__spec__.parent, ".main"),
-    "pause_flow_run": (__spec__.parent, ".main"),
-    "resume_flow_run": (__spec__.parent, ".main"),
-    "suspend_flow_run": (__spec__.parent, ".main"),
 }
 
 # Declare API for type-checkers
 __all__ = [
+    "__development_base_path__",
+    "__module_path__",
+    "__ui_static_path__",
+    "__ui_static_subpath__",
+    "__version__",
+    "__version_info__",
     "allow_failure",
+    "aserve",
+    "deploy",
     "flow",
     "Flow",
     "get_client",
     "get_run_logger",
+    "pause_flow_run",
+    "resume_flow_run",
+    "serve",
     "State",
+    "suspend_flow_run",
     "tags",
     "task",
     "Task",
     "Transaction",
     "unmapped",
-    "serve",
-    "aserve",
-    "deploy",
-    "pause_flow_run",
-    "resume_flow_run",
-    "suspend_flow_run",
-    "__version_info__",
-    "__version__",
-    "__module_path__",
-    "__development_base_path__",
-    "__ui_static_subpath__",
-    "__ui_static_path__",
 ]
 
 
-def __getattr__(attr_name: str) -> object:
-    if attr_name in _slots:
-        return _slots[attr_name]
-    try:
-        dynamic_attr = _public_api.get(attr_name)
-        if dynamic_attr is None:
-            return importlib.import_module(f".{attr_name}", package=__name__)
-
-        package, module_name = dynamic_attr
+def __getattr__(attr_name: str) -> Any:
+    if (dynamic_attr := _public_api.get(attr_name)) is None:
+        return importlib.import_module(f".{attr_name}", package=__name__)
 
-        from importlib import import_module
+    package, mname = dynamic_attr
 
-        if module_name == "__module__":
-            return import_module(f".{attr_name}", package=package)
+    try:
+        if mname == "__module__":
+            return importlib.import_module(f".{attr_name}", package=package)
         else:
-            module = import_module(module_name, package=package)
+            module = importlib.import_module(mname, package=package)
             return getattr(module, attr_name)
     except ModuleNotFoundError as ex:
-        module, _, attribute = ex.name.rpartition(".")
-        raise AttributeError(f"module {module} has no attribute {attribute}") from ex
+        mname, _, attr = (ex.name or "").rpartition(".")
+        ctx = {"name": mname, "obj": attr} if sys.version_info >= (3, 10) else {}
+        raise AttributeError(f"module {mname} has no attribute {attr}", **ctx) from ex