I have a list of dictionaries:

history_changes = [
{'userName': 'recg', 'modificationDate': '2022-07-14T04:01:39+00:00', 'changeComment': 'more details about L2'},
{'userName': 'artf', 'modificationDate': '2022-07-15T04:01:39+00:00', 'changeComment': 'more details about L1'},
{'username': 'zrt',  'modificationDate': '2022-07-16T04:01:39+00:00', 'changeComment': 'more details about L3'}]

I’m iterating over it and trying to insert data in a database.

for record in history_changes[1:]:
   comment = record['changeComment']
   to_time = record['modificationDate']

I also need the "start_time" information which is the ‘modificationDate’ from the previous dictionary.

Expected output:

 comment = 'more details about L1'
 start_time = '2022-07-14T04:01:39+00:00'
 to_time = '2022-07-15T04:01:39+00:00'

 comment = 'more details about L3'
 start_time = '2022-07-15T04:01:39+00:00'
 to_time = '2022-07-16T04:01:39+00:00'
 

How can I get the 'modificationDate' from the previous dictionary when iterating over the list?

>Solution :

history_changes = [
{'userName': 'recg', 'modificationDate': '2022-07-14T04:01:39+00:00', 'changeComment': 'more details about L2'},
{'userName': 'artf', 'modificationDate': '2022-07-15T04:01:39+00:00', 'changeComment': 'more details about L1'},
{'username': 'zrt',  'modificationDate': '2022-07-16T04:01:39+00:00', 'changeComment': 'more details about L3'}]


for x in range(1,len(history_changes)):  # see here I am starting from 1 index 
    print(history_changes[x]['changeComment'])
    print(history_changes[x-1]['modificationDate'])
    print(history_changes[x]['modificationDate'])

#output
more details about L1
2022-07-14T04:01:39+00:00
2022-07-15T04:01:39+00:00
more details about L3
2022-07-15T04:01:39+00:00
2022-07-16T04:01:39+00:00

If you want to store these value then:

comment=[]
start_time=[]
to_time=[]
for x in range(1,len(history_changes)):
    comment.append(history_changes[x]['changeComment'])
    start_time.append(history_changes[x-1]['modificationDate'])
    to_time.append(history_changes[x]['modificationDate'])