change item in column based on the item before[solved]

[amdi40]

I have also tried

import os
from pathlib import Path
import pandas as pd
import datetime

def convert_file():
    # Set start directory same as script
    os.chdir(os.path.abspath(os.path.dirname(__file__)))

    infile = Path('.') / 'gauga20211_19790101-20120101.txt'
    outfile = Path('.') / 'newfile.csv'

    with infile.open() as fp, outfile.open('w') as fout:
        startdate = None
        starttime = None
        nexttime = 0
        for line in fp:
            line = line.strip().split()
            # extract header
            if line[0] == '1':
                startdate = pd.to_datetime(line[1], format='%Y%m%d')
                starttime = pd.to_datetime(line[2], format='%H%M')
                nexttime = starttime
            else:
                for item in line:
                    data = f"{startdate}-{starttime},{item}\n"
                    fout.write(data)
                    nexttime += datetime.timedelta(minutes=2)
if __name__ == '__main__':
    convert_file()

The date format is however not as i try to format it, and the desired deltatime is not added

Output:
1979-01-11 00:00:00-1900-01-01 10:07:00,3.333
1979-01-11 00:00:00-1900-01-01 10:07:00,3.333
1979-01-11 00:00:00-1900-01-01 10:07:00,3.333
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,0.556
1979-01-11 00:00:00-1900-01-01 10:07:00,3.333
1979-01-11 00:00:00-1900-01-01 10:07:00,0.370
1979-01-11 00:00:00-1900-01-01 10:07:00,0.370
1979-01-11 00:00:00-1900-01-01 10:07:00,0.370