I get warnings about low memory (2% left) in my machine from status_check.py. It is an virtual machine inside LXC running Ubuntu 14.04. I have no problem with memory so psutil is wrong.
root@mail:~# free -h
total used free shared buffers cached
Mem: 31G 456M 30G 63M 0B 5K
-/+ buffers/cache: 456M 30G
Swap: 2,0G 1,3G 673M
root@mail:~# /usr/bin/python3
Python 3.4.3 (default, Nov 17 2016, 01:08:31)
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import psutil
>>> percent_free = 100 - psutil.virtual_memory().percent
>>> memory_msg = "System memory is %s%% free." % str(round(percent_free))
>>> print(memory_msg)
System memory is 2% free.
>>> psutil.virtual_memory()
svmem(total=33709006848, available=606629888, percent=98.2, used=33280512000, free=428494848, active=321347584, inactive=0, buffers=178126848, cached=8192, shared=66088960)