python - KeyError when appending to a dictionary of lists -

i want use dictionary record data relating ip addresses, ip address can have number of groups associated it, , need capture info groups relating ip address (these controller groups on wireless system data relating configuration of access points). want like:

{<ip_addr>: [{group_name: my_aps, total_aps: 22, total_active_aps: 12},              {group_name: my-other_aps, total_aps: 15, total_active_aps:14},              {...}             ] } 

my script looping through list of groups (there 300+) , pulling info off wireless controller. each loop obtain details of new group. can't work out how add group dictionary list. trying (where group_details group dictionary , lms_ip address want list against):

lms_groups[lms_ip].append(group_details) 

but get:

keyerror: 'xxx.xxx.xxx.xxx' 

(ip address hidden fwiw)

the script seems work point, think dictionaries being created ok.

option 1

dict.setdefault

lms_groups.setdefault(lms_ip, []).append(group_details) 

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option 2

collections.defaultdict

from collections import defaultdict     lms_groups = defaultdict(list) ... lms_groups[lms_ip].append(group_details)