Can someone help me to figure out the error...
 
#! /usr/bin/python
import sys
import ssl
import pprint
sys.path.append("C:/Python/netapp-manageability-sdk-5.6/lib/python/NetApp")
from NaServer import *
from NaElement import *
ssl._create_default_https_context = ssl._create_unverified_context
try:
    _create_unverified_https_context = ssl._create_unverified_context
except AttributeError:
    # Legacy Python that doesn't verify HTTPS certificates by default
    pass
else:
    # Handle target environment that doesn't support HTTPS verification
    ssl._create_default_https_context = _create_unverified_https_context
def print_usage():
    print ("Usage: hello_ontapi.py <filer> <user> <password> \n")
    print ("<filer> -- Filer name\n")
    print ("<user> -- User name\n")
    print ("<password> -- Password\n")
    sys.exit (1)
args = len(sys.argv) - 1
if(args < 3😞
   print_usage()
filer = sys.argv[1]
user = sys.argv[2]
password = sys.argv[3]
s = NaServer(filer, 1, 6)
s.set_server_type("Filer")
s.set_admin_user(user, password)
s.set_transport_type("HTTPS")
output = s.invoke("system-get-version")
if(output.results_errno() != 0😞
   r = output.results_reason()
   print("Failed: \n" + str(r))
else :
   r = output.child_get_string("version")
   print (r + "\n")
cmd = NaElement("volume-list-info")
ret = s.invoke_elem(cmd)
volumes = ret.child_get("volumes")
for vol in volumes.children_get():
    print(vol.child_get_string("name"))
    print(vol.child_get_int("size-total"))
    print(vol.child_get_string("mirror-status"))
    print(vol.child_get_int("snapshot-percent-reserved"))
    cmd1 = NaElement("snapshot-list-info")
    cmd1.child_add_string("volume", vol.child_get_string("vol0"))  # This is where you set the volume name
    ret1 = s.invoke_elem(cmd1)
    snaps = ret1.child_get("snapshots")
    for snap in snaps.children_get():
        print(snap.child_get_string("name"))
Output:
NetApp Release 9.3RC1: Wed Nov 01 07:34:37 UTC 2017
Traceback (most recent call last):
 File "C:\Python\PycharmProjects\Storage\NetApp-Cluster-HC\Quota repport.py", line 47, in <module>
 for vol in volumes.children_get():
AttributeError: 'NoneType' object has no attribute 'children_get'