How to group a list of lists into a new list based on the beginning character of one of the elements in one of the lists

I have a lists of lists called "lines" that looks like this:

[['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
['REF', '0F', '708066255'],
['REF', '1L', '708066255'],
['DTP', '303', 'D8', '20240901'],
['DTP', '356', 'D8', '20240801'],
['NM1', 'IL', '1', 'FIGUEROA', 'LILIET', '', '', '', '34', '536899858'],
['N3', '2670 SO A W GRIMES BO', '#6102'],
['N4', 'ROUND ROCK', 'TX', '786642849', '', 'CY', '246'],
['DMG', 'D8', '19931219', 'F', '', 'H'],
['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
['REF', '0F', '811229070'],
['REF', '1L', '811229070'],
['DTP', '303', 'D8', '20240901'],
['DTP', '356', 'D8', '20240201'],
['NM1', 'IL', '1', 'MORILLO RUZA', 'OMARLY', 'V', '', '', '34', '000000000'],
['PER', 'IP', '', 'HP', '5129233526'],
['N3', '154 TERRI TL'],
['N4', 'ELGIN', 'TX', '786218937', '', 'CY', '011'],
['DMG', 'D8', '20040628', 'F', '', 'H']]

What I need is to group the lists into new lists wherever the 'INS' element appears in one of the lists. The output should look like:

[[['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
['REF', '0F', '708066255'],
['REF', '1L', '708066255'],
['DTP', '303', 'D8', '20240901'],
['DTP', '356', 'D8', '20240801'],
['NM1', 'IL', '1', 'FIGUEROA', 'LILIET', '', '', '', '34', '536899858'],
['N3', '2670 SO A W GRIMES BO', '#6102'],
['N4', 'ROUND ROCK', 'TX', '786642849', '', 'CY', '246'],
['DMG', 'D8', '19931219', 'F', '', 'H']],
[['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
['REF', '0F', '811229070'],
['REF', '1L', '811229070'],
['DTP', '303', 'D8', '20240901'],
['DTP', '356', 'D8', '20240201'],
['NM1', 'IL', '1', 'MORILLO RUZA', 'OMARLY', 'V', '', '', '34', '000000000'],
['PER', 'IP', '', 'HP', '5129233526'],
['N3', '154 TERRI TL'],
['N4', 'ELGIN', 'TX', '786218937', '', 'CY', '011'],
['DMG', 'D8', '20040628', 'F', '', 'H']]]

Im unsure how to do this

Solution

iterate through intial list, check if first element is INS or not, and based on that structure your final output

below is example

x = [
        ['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
        ['REF', '0F', '708066255'], ['REF', '1L', '708066255'],
        ['DTP', '303', 'D8', '20240901'],
        ['DTP', '356', 'D8', '20240801'],
        ['NM1', 'IL', '1', 'FIGUEROA', 'LILIET', '', '', '', '34', '536899858'],
        ['N3', '2670 SO A W GRIMES BO', '#6102'],
        ['N4', 'ROUND ROCK', 'TX', '786642849', '', 'CY', '246'],
        ['DMG', 'D8', '19931219', 'F', '', 'H'],
        ['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
        ['REF', '0F', '811229070'],
        ['REF', '1L', '811229070'],
        ['DTP', '303', 'D8', '20240901'],
        ['DTP', '356', 'D8', '20240201'],
        ['NM1', 'IL', '1', 'MORILLO RUZA', 'OMARLY', 'V', '', '', '34', '000000000'], 
        ['PER', 'IP', '', 'HP', '5129233526'], 
        ['N3', '154 TERRI TL'], 
        ['N4', 'ELGIN', 'TX', '786218937', '', 'CY', '011'], 
        ['DMG', 'D8', '20040628', 'F', '', 'H']
]

sol = []
tmp = []



for i in x:
    if i[0]!="INS":
        tmp.append(i)
    else:
        if tmp:
            sol.append(tmp)
        tmp = [i]

if tmp:
    sol.append(tmp)

print(sol)

# output
"""
[
    [
        ['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
        ['REF', '0F', '708066255'],
        ['REF', '1L', '708066255'],
        ['DTP', '303', 'D8', '20240901'],
        ['DTP', '356', 'D8', '20240801'],
        ['NM1', 'IL', '1', 'FIGUEROA', 'LILIET', '', '', '', '34', '536899858'],
        ['N3', '2670 SO A W GRIMES BO', '#6102'],
        ['N4', 'ROUND ROCK', 'TX', '786642849', '', 'CY', '246'],
        ['DMG', 'D8', '19931219', 'F', '', 'H']
    ],
    [
        ['INS', 'Y', '18', '024', '07', 'A', '', '', 'TE'],
        ['REF', '0F', '811229070'],
        ['REF', '1L', '811229070'],
        ['DTP', '303', 'D8', '20240901'],
        ['DTP', '356', 'D8', '20240201'],
        ['NM1', 'IL', '1', 'MORILLO RUZA', 'OMARLY', 'V', '', '', '34', '000000000'],
        ['PER', 'IP', '', 'HP', '5129233526'],
        ['N3', '154 TERRI TL'],
        ['N4', 'ELGIN', 'TX', '786218937', '', 'CY', '011'],
        ['DMG', 'D8', '20040628', 'F', '', 'H']
    ]
]
"""