如何 append 到 csv 文件中的用户指定行？

Question

Context:

Hello - I need to append the word "CANCELLED" to the end of the specified line in a csv file. The user of this program is asked to input (search for) a last name. If the last name is found in the CSV file, the word "CANCELLED" should be added to the very end of the line containing that last name.

Problem:

With the code I currently have, the line prints correctly as it should appear in the csv file. However, it is not being saved to the csv file for some reason.

Code is attached - please let me know if I could be more clear. thanks!

elif menuSelect == "7":
    print("CXL MENU")
    print("---------")
    print("1. Cancel by Last Name \n")
    print("2. Cancel by Confirmation #\n")
    cancelSelect = input("Select an option: ")
    lastName = input("Enter Last Name: ")
    ResStatus = "CANCELLED"
    if cancelSelect == "1":
        #open csv file, search for lastName input
        with open ('hotelguests.csv', 'rt') as csv_file:
            csv_reader = csv.reader(csv_file, delimiter=',')
            for row in csv_reader:
                if row[0] == lastName:
                    #Write ResStatus variable to row containing lastName input
                    with open ('hotelguests.csv', 'w') as csv_file:
                        csvwriter = csv.writer(csv_file)
                        csvwriter.writerow([ResStatus])
                        print(row)

Answer 1

Here's a technique I invented a while back in an effort to make re-writing CSV files relatively easy by leveraging the capabilities of the fileinput module that's in Python's standard library.

It works by creating a temporary file and storing everything printed into it, and then effectively replaces the original file with that when it's finished. In the code below a copy of original file with the extension .sav appended to it is saved (an optional feature, see the documentation).

Here's how to use it to do what you want:

import csv
import fileinput

file_name = 'hotelguests.csv'
#cancelSelect = input("Select an option: ")
cancelSelect = "1"
#lastName = input("Enter Last Name: ")
lastName = "Trump"
ResStatus = "CANCELLED"
if cancelSelect == "1":
    with fileinput.FileInput(files=file_name, inplace=True, backup='.sav') as csvfile:
        for row in csv.reader(csvfile):
            if row[0] == lastName:
                row.append(ResStatus)
            print(','.join(row))  # Print as comma-separated list of values.
    print('file updated')