[Serve] Only install dataclasses on Python 3.6 (#10936)

python/requirements.txt

@@ -38,13 +38,13 @@ tabulate
 tensorboardX
 uvicorn
 pydantic
-dataclasses
+dataclasses; python_version < '3.7'
 
 # Requirements for running tests
 blist; platform_system != "Windows"
 boto3
 cython==0.29.0
-dataclasses
+dataclasses; python_version < '3.7'
 dask[complete]
 feather-format
 gym

python/setup.py

@@ -110,8 +110,14 @@ if os.getenv("RAY_USE_NEW_GCS") == "on":
 # in this directory
 extras = {
     "debug": [],
-    "serve": ["uvicorn", "flask", "requests", "pydantic", "dataclasses"],
-    "tune": ["tabulate", "tensorboardX", "pandas", "dataclasses"]
+    "serve": [
+        "uvicorn", "flask", "requests", "pydantic",
+        "dataclasses; python_version < '3.7'"
+    ],
+    "tune": [
+        "tabulate", "tensorboardX", "pandas",
+        "dataclasses; python_version < '3.7'"
+    ]
 }
 
 extras["rllib"] = extras["tune"] + [