diff --git a/dev_requirement.txt b/dev_requirement.txt
index f95a7eb..e87267f 100644
--- a/dev_requirement.txt
+++ b/dev_requirement.txt
@@ -18,7 +18,9 @@ openvpn-status==0.2.1
 parso==0.6.2
 pexpect==4.8.0
 pickleshare==0.7.5
+pkg-resources==0.0.0
 prompt-toolkit==3.0.5
+psutil==5.7.0
 ptyprocess==0.6.0
 pycodestyle==2.5.0
 Pygments==2.6.1
@@ -26,7 +28,9 @@ pylint==2.4.4
 python-dateutil==2.8.1
 pyzmq==19.0.0
 six==1.14.0
+tailer==0.4.1
 tornado==6.0.4
 traitlets==4.3.3
+typed-ast==1.4.1
 wcwidth==0.1.9
 wrapt==1.11.2
diff --git a/o_manager.py b/o_manager.py
index 40d1761..1bc26e2 100644
--- a/o_manager.py
+++ b/o_manager.py
@@ -129,8 +129,7 @@ class OManager:
         n_down = 2
         weights = []
         for i in self.instances:
-            ping_stat = i["op"].get_ping_stat(
-            ).splitlines()[-max(n_up, n_down):]
+            ping_stat = i["op"].get_ping_stat(lines=max(n_up, n_down))
             ping_stat = [i.split(",")[-1] != "-1" for i in ping_stat]
             #print("ping status:", ping_stat)
             def all_equal(n, status):