From df247fb33a3a3f974664c0079663069c5dea2d20 Mon Sep 17 00:00:00 2001
From: Richard Belleville <rbellevi@google.com>
Date: Mon, 10 Feb 2020 16:47:43 -0800
Subject: [PATCH] Experimental API decorator

---
 src/python/grpcio/grpc/_simple_stubs.py       |  9 ++++---
 .../grpcio/grpc/experimental/__init__.py      | 25 ++++++++++++++++---
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/src/python/grpcio/grpc/_simple_stubs.py b/src/python/grpcio/grpc/_simple_stubs.py
index 3edf72c3422..378c234cd15 100644
--- a/src/python/grpcio/grpc/_simple_stubs.py
+++ b/src/python/grpcio/grpc/_simple_stubs.py
@@ -22,6 +22,7 @@ from typing import (Any, AnyStr, Callable, Dict, Iterator, Optional, Sequence,
                     Tuple, TypeVar, Union)
 
 import grpc
+from grpc.experimental import experimental_api
 
 RequestType = TypeVar('RequestType')
 ResponseType = TypeVar('ResponseType')
@@ -169,6 +170,7 @@ class ChannelCache:
 
 
 # pylint: disable=too-many-arguments
+@experimental_api
 def unary_unary(
         request: RequestType,
         target: str,
@@ -228,7 +230,6 @@ def unary_unary(
     Returns:
       The response to the RPC.
     """
-    grpc.experimental.warn_experimental("unary_unary")
     channel = ChannelCache.get().get_channel(target, options,
                                              channel_credentials, compression)
     multicallable = channel.unary_unary(method, request_serializer,
@@ -241,6 +242,7 @@ def unary_unary(
 
 
 # pylint: disable=too-many-arguments
+@experimental_api
 def unary_stream(
         request: RequestType,
         target: str,
@@ -299,7 +301,6 @@ def unary_stream(
     Returns:
       An iterator of responses.
     """
-    grpc.experimental.warn_experimental("unary_stream")
     channel = ChannelCache.get().get_channel(target, options,
                                              channel_credentials, compression)
     multicallable = channel.unary_stream(method, request_serializer,
@@ -312,6 +313,7 @@ def unary_stream(
 
 
 # pylint: disable=too-many-arguments
+@experimental_api
 def stream_unary(
         request_iterator: Iterator[RequestType],
         target: str,
@@ -370,7 +372,6 @@ def stream_unary(
     Returns:
       The response to the RPC.
     """
-    grpc.experimental.warn_experimental("stream_unary")
     channel = ChannelCache.get().get_channel(target, options,
                                              channel_credentials, compression)
     multicallable = channel.stream_unary(method, request_serializer,
@@ -383,6 +384,7 @@ def stream_unary(
 
 
 # pylint: disable=too-many-arguments
+@experimental_api
 def stream_stream(
         request_iterator: Iterator[RequestType],
         target: str,
@@ -441,7 +443,6 @@ def stream_stream(
     Returns:
       An iterator of responses.
     """
-    grpc.experimental.warn_experimental("stream_stream")
     channel = ChannelCache.get().get_channel(target, options,
                                              channel_credentials, compression)
     multicallable = channel.stream_stream(method, request_serializer,
diff --git a/src/python/grpcio/grpc/experimental/__init__.py b/src/python/grpcio/grpc/experimental/__init__.py
index 29f499f57c6..93ed0f64291 100644
--- a/src/python/grpcio/grpc/experimental/__init__.py
+++ b/src/python/grpcio/grpc/experimental/__init__.py
@@ -16,11 +16,14 @@
 These APIs are subject to be removed during any minor version release.
 """
 
+import functools
 import sys
 import warnings
 
 import grpc
 
+_EXPERIMENTAL_APIS_USED = set()
+
 
 class ChannelOptions(object):
     """Indicates a channel option unique to gRPC Python.
@@ -56,16 +59,30 @@ class ExperimentalApiWarning(Warning):
     """A warning that an API is experimental."""
 
 
-def warn_experimental(api_name):
-    msg = ("{} is an experimental API. It is subject to change or ".format(
-        api_name) + "removal between minor releases. Proceed with caution.")
-    warnings.warn(msg, ExperimentalApiWarning, stacklevel=2)
+def _warn_experimental(api_name, stack_offset):
+    if api_name not in _EXPERIMENTAL_APIS_USED:
+        _EXPERIMENTAL_APIS_USED.add(api_name)
+        msg = ("'{}' is an experimental API. It is subject to change or ".
+               format(api_name) +
+               "removal between minor releases. Proceed with caution.")
+        warnings.warn(msg, ExperimentalApiWarning, stacklevel=2 + stack_offset)
+
+
+def experimental_api(f):
+
+    @functools.wraps(f)
+    def _wrapper(*args, **kwargs):
+        _warn_experimental(f.__name__, 1)
+        return f(*args, **kwargs)
+
+    return _wrapper
 
 
 __all__ = (
     'ChannelOptions',
     'ExperimentalApiWarning',
     'UsageError',
+    'experimental_api',
     'insecure_channel_credentials',
 )