Fix fail on Python 3.7

Author: standy66

.travis.yml

@@ -1,5 +1,7 @@
 sudo: required
-language: generic
+language: python
+python:
+  - "3.6"
 services:
   - docker
 env:
@@ -9,10 +11,14 @@ env:
 script:
   - ./ci/run_tests_in_docker.sh $PYTHON_IMAGE
 
-deploy:
-  provider: pypi
-  user: "$TWINE_USER"
-  password: "$TWINE_PASSWORD"
-  distributions: "sdist bdist_wheel"
-  on:
-    tags: true
+jobs:
+  include:
+    - stage: deploy
+      skript: skip
+      deploy:
+        provider: pypi
+        user: "$TWINE_USER"
+        password: "$TWINE_PASSWORD"
+        distributions: "sdist bdist_wheel"
+        on:
+          tags: true

src/purerpc/rpc.py

@@ -1,5 +1,6 @@
 import enum
 import typing
+import collections
 
 
 Stream = typing.AsyncIterator
@@ -43,14 +44,16 @@ def response_type(self):
 
     @staticmethod
     def from_annotations(request_annotation, response_annotation):
-        if issubclass(request_annotation, Stream):
+        if (hasattr(request_annotation, "__origin__") and
+                issubclass(request_annotation.__origin__, collections.abc.AsyncIterator)):
             request_type = request_annotation.__args__[0]
             request_stream = True
         else:
             request_type = request_annotation
             request_stream = False
 
-        if issubclass(response_annotation, Stream):
+        if (hasattr(response_annotation, "__origin__") and
+                issubclass(response_annotation.__origin__, collections.abc.AsyncIterator)):
             response_type = response_annotation.__args__[0]
             response_stream = True
         else: