add etcd version hint

.travis.yml

@@ -16,9 +16,13 @@ services:
 services:
   - docker
 
+env:
+  matrix:
+    - ETCD_VER=v3.3
+
 before_install:
-  - docker pull quay.io/coreos/etcd:v3.3
-  - docker run -d -p 2379:2379 -p 2380:2380 --name etcd3 quay.io/coreos/etcd:v3.3 etcd --name node1 --initial-advertise-peer-urls http://0.0.0.0:2380 --listen-peer-urls http://0.0.0.0:2380 --advertise-client-urls http://0.0.0.0:2379 --listen-client-urls http://0.0.0.0:2379 --initial-cluster node1=http://0.0.0.0:2380
+  - docker pull quay.io/coreos/etcd:$ETCD_VER
+  - docker run -d -p 2379:2379 -p 2380:2380 --name etcd3 quay.io/coreos/etcd:$ETCD_VER etcd --name node1 --initial-advertise-peer-urls http://0.0.0.0:2380 --listen-peer-urls http://0.0.0.0:2380 --advertise-client-urls http://0.0.0.0:2379 --listen-client-urls http://0.0.0.0:2379 --initial-cluster node1=http://0.0.0.0:2380
   - docker ps
   - sudo docker cp etcd3:/usr/local/bin/etcdctl /usr/bin/etcdctl
   - which etcdctl
@@ -39,6 +43,6 @@ deploy:
     secure: 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
   on:
     tags: true
-    branch: master
-    python:
-      - 3.6
+#    branch: master
+#    python:
+#      - 3.6

README.md

@@ -12,8 +12,9 @@ Python client for etcd v3 (Using gRPC-JSON-Gateway)
 * Free software: Apache Software License 2.0
 * Source Code: https://github.com/Revolution1/etcd3-py
 * Documentation: https://etcd3-py.readthedocs.io.
+* etcd version required: v3.3.0+
 
-Notice: The authentication header through gRPC-JSON-Gateway only supported in [etcd v3.3+](https://github.com/coreos/etcd/pull/7999)
+Notice: The authentication header through gRPC-JSON-Gateway only supported in [etcd v3.3.0+](https://github.com/coreos/etcd/pull/7999)
 
 ## Features
 
@@ -136,6 +137,22 @@ user2 got the lock
 user2 releasing the lock
 ```
 
+**Start a single-node etcd using docker**
+```bash
+export NODE1=0.0.0.0
+export ETCD_VER=v3.3
+docker run -d \
+-p 2379:2379 \
+-p 2380:2380 \
+--volume=/tmp/etcd3-data:/etcd-data \
+--name etcd3 quay.io/coreos/etcd:$ETCD_VER \
+/usr/local/bin/etcd \
+--data-dir=/etcd-data --name node1 \
+--initial-advertise-peer-urls http://${NODE1}:2380 --listen-peer-urls http://${NODE1}:2380 \
+--advertise-client-urls http://${NODE1}:2379 --listen-client-urls http://${NODE1}:2379 \
+--initial-cluster node1=http://${NODE1}:2380
+```
+
 ## TODO
 
 - [ ] benchmark

etcd3/baseclient.py

@@ -6,7 +6,6 @@
 import os
 import warnings
 
-import requests
 import semantic_version as sem
 from six.moves import urllib_parse
 
@@ -78,17 +77,19 @@ def __init__(self, host='localhost', port=2379, protocol='http',
 
     def _retrieve_version(self):  # pragma: no cover
         try:
-            r = requests.get(self._url('/version'), timeout=0.3)
+            import requests
+
+            r = requests.get(self._url('/version'), timeout=0.3) # 300ms will do
             r.raise_for_status()
             v = r.json()
             self.cluster_version = v["etcdcluster"]
             if sem.compare(self.cluster_version, '3.3.0') == -1:
                 warnings.warn(Etcd3Warning("detected etcd cluster version(%s) is lower than 3.3.0, "
-                                           "auth method may not work" % self.cluster_version))
+                                           "the gRPC-JSON-Gateway may not work" % self.cluster_version))
         except Exception:
             warnings.warn(Etcd3Warning("cannot detect etcd server version\n"
                                        "1. maybe is a network problem, please check your network connection\n"
-                                       "2. maybe your etcd server version is too low, recommended: 3.3.0+"))
+                                       "2. maybe your etcd server version is too low, required: 3.3.0+"))
 
     @property
     def baseurl(self):