数据未追加到我的输出文件中，python csv模块3.6

Question

I am a newbie to python world, need help

I have a requirement to remove the duplicate values from row3 and append the data of row4, I am using below script to achieve this

Everything works fine except the data in the row4 is not getting appended

Appreciate your help on this

import csv

result = {}

with open('test.csv', 'r') as csv_file:
    csv_reader = csv.DictReader(csv_file)

    with open('output.csv', 'w',encoding='utf-8') as new_file:
        fieldnames = ['row1','row2','row3','row4','row5',]
        csv_writer = csv.DictWriter(new_file,lineterminator='\n' , fieldnames=fieldnames)
        csv_writer.writeheader ()

        for row in csv_reader:
           if row["row3"] in result:
               result [row["row3"]].append (row["row4"])
           else:
               result[row["row3"]] = [row["row4"]]
           csv_writer.writerow({
            "row1":  row["row1"],
            "row2": row["row2"],
            "row3": row["row3"],
            "row4": row["row4"],
            "row4": row["row4"]
            })

Answer 1

Change the 'w' to 'a' in the line:

with open('output.csv', 'w',encoding='utf-8') as new_file:

a is for appending to the file. w is for write, which will overwrite any previous files.

Refer to https://docs.python.org/3/tutorial/inputoutput.html for python file input and outputs