Address the code review by Alex.

patroni/etcd.py

@@ -236,8 +236,8 @@ class Etcd(AbstractDCS):
         return self.retry(self.client.test_and_set, self.leader_path, self._name, self._name, self.ttl)
 
     @catch_etcd_errors
-    def initialize(self, create_new=True, sysid=None):
-        return self.retry(self.client.write, self.initialize_path, sysid or "", prevExist=(not create_new))
+    def initialize(self, create_new=True, sysid=""):
+        return self.retry(self.client.write, self.initialize_path, sysid, prevExist=(not create_new))
 
     @catch_etcd_errors
     def delete_leader(self):

patroni/postgresql.py

@@ -101,16 +101,13 @@ class Postgresql:
             return False
         # check if the cluster's configuration permits pg_rewind
         data = self.controldata()
-        if data:
-            return data.get('wal_log_hints setting', 'off') == 'on' or\
-                data.get('Data page checksum version', '0') != '0'
-        return False
+        return data.get('wal_log_hints setting', 'off') == 'on' or data.get('Data page checksum version', '0') != '0'
 
     @property
     def sysid(self):
         if not self._sysid:
             data = self.controldata()
-            self._sysid = data and data.get('Database system identifier', None)
+            self._sysid = data.get('Database system identifier', "")
         return self._sysid
 
     def require_rewind(self):
@@ -399,7 +396,7 @@ recovery_target_timeline = 'latest'
         try:
             data = subprocess.check_output(['pg_controldata', self.data_dir])
             if data:
-                data = data.splitlines()
+                data = data.decode().splitlines()
                 result = {l.split(':')[0].replace('Current ', '', 1): l.split(':')[1].strip() for l in data if l}
         except subprocess.CalledProcessError:
             logger.exception("Error when calling pg_controldata")

patroni/zookeeper.py

@@ -139,7 +139,7 @@ class ZooKeeper(AbstractDCS):
             self.fetch_cluster = True
 
         # get initialize flag
-        initialize = self.get_node(self._INITIALIZE)[0] if self._INITIALIZE in nodes else None
+        initialize = self.get_node(self.initialize_path)[0] if self._INITIALIZE in nodes else None
 
         # get list of members
         members = self.load_members() if self._MEMBERS[:-1] in nodes else []
@@ -203,9 +203,9 @@ class ZooKeeper(AbstractDCS):
             logging.exception('set_failover_value')
             return False
 
-    def initialize(self, create_new=True, sysid=None):
-        return self._create(self.initialize_path, sysid if sysid else "", makepath=True) if create_new \
-            else self.client.retry(self.client.set, self.initialize_path,  sysid.encode("utf-8") if sysid else "")
+    def initialize(self, create_new=True, sysid=""):
+        return self._create(self.initialize_path, sysid, makepath=True) if create_new \
+            else self.client.retry(self.client.set, self.initialize_path,  sysid.encode("utf-8"))
 
     def touch_member(self, data, ttl=None):
         cluster = self.cluster

tests/test_postgresql.py

@@ -86,7 +86,7 @@ class MockConnect(Mock):
 
 
 def pg_controldata_string(*args, **kwargs):
-    return """
+    return b"""
 pg_control version number:            942
 Catalog version number:               201509161
 Database system identifier:           6200971513092291716