L103 Draft: Add Types to the remainder of the gRPC Python API Surface

L103-python-add-typing-to-sync-api.md

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+Add Typing to gRPC Python Sync API
+----
+* Author(s): XuanWnag-Amos
+* Approver: gnossen
+* Status: Draft
+* Implemented in: Python
+* Last updated: 11/09/2022
+* Discussion at: <google group thread> (filled after thread exists)
+
+## Abstract
+
+Add type annotation to Python Sync API.
+
+## Background
+
+[Type Hints](https://peps.python.org/pep-0484/#union-types) was introduced for a while now, we already added type annotation to python Async APIs since it has a high enough version floor. Now it's time to do the same for Sync APIs.
+
+This proposal plans to add type annotation to python Sync public APIs which allows users to build safer code by running static type analysis tools.
+
+
+### Related Proposals: 
+* Loosely related: https://github.com/lidizheng/proposal/blob/grpc-python-async-api/L58-python-async-api.md#introduce-typing-to-generated-code
+  * The proposal includes the part to introduce typing to gRPC Python Async APIs.
+
+
+## Proposal
+
+Add type annotation to the following Python APIs:
+* All APIs in `__init__.py` (the actuall list is too long, please refer to following PR for changes):
+  * [PR link holder]
+* `grpc/src/python/grpcio/grpc/_runtime_protos.py`
+```python
+def protos(protobuf_path):  # pylint: disable=unused-argument
+  ...
+
+def services(protobuf_path):  # pylint: disable=unused-argument
+  ...
+
+def protos_and_services(protobuf_path):  # pylint: disable=unused-argument
+  ...
+```
+
+## Rationale
+
+The alternative is keep APIs in Sync stack unchanged and without type annotation, this way users won't be able to know if their implementation is correct or not without actually running the code.
+
+After add type annotation, instead of original un-typed API (`UnaryUnaryMultiCallable.__call__`):
+```python
+@abc.abstractmethod
+def __call__(self,
+             request,
+             timeout=None,
+             metadata=None,
+             credentials=None,
+             wait_for_ready=None,
+             compression=None):
+```
+
+We'll have typed API which will looks like this:
+```python
+@abc.abstractmethod
+def __call__(self,
+             request: RequestType,
+             timeout: Optional[float] = None,
+             metadata: Optional[MetadataType] = None,
+             credentials: Optional[CallCredentials] = None,
+             wait_for_ready: Optional[bool] = None,
+             compression: Optional[Compression] = None) -> ResponseType:
+```
+
+## Implementation
+
+1. Add typing to internal APIs.
+2. Add typing to public API and test though pre-release.
+3. Add typing to public APIs.
+
+## Open issues (if applicable)
+
+N/A