Add extra column as the cumulative time difference

Question

How to add an extra column that is the cumulative value of the time differences for each course? For example, the initial table is:

 id_A       course     we         


        

Answer 1

import csv
import datetime as dt

with open('path/to/input') as fin, open('path/to/output', 'w') as fout:
    infile = csv.DictReader(fin, delimiter='\t')
    outfile = csv.DictWriter(fout, delimiter='\t', fieldnames=infile.fieldnames + ['cum_delta_sec'])

    cdt = 0
    last = None
    for row in infile:
        if last is None:
            last = dt.strptime(row['ts_A'], "%Y-%m-%d %H:%M:%S")
            row['cum_delta_sec'] = 0
            outfile.writerow(row)
            continue

        cdt += (last - dt.strptime(row['ts_A'], "%Y-%m-%d %H:%M:%S")).total_seconds()
        row['cum_delta_sec'] = cdt
        outfile.writerow(row)