如何在 csv 中仅重写一个字段（行[n]）但同时能够处理数据？

Question

我这里有一个三行三列的 csv 文件。

This is the csv file

起初我想打印所有的行。随后，对于它们中的每一个，程序检查它是否写在第二个字段（索引 1）USA 中。如果是这样，程序将从第三个字段中获取价格并将其乘以二。

现在我需要重写这个双倍价格而不是 2000（与美国一致）

import csv

with open('countries.csv', 'r') as source:
    reader = csv.reader(source)
    writer = csv.writer(source)

    for line in reader: 
        print(*line, sep=';')

with open('countries.csv', 'r') as source: 
    reader = csv.reader(source)

    for line in reader:
        if line[2] == "USA":
            actual_price = int(line[2])
            print(actual_price)
            new_price = int(actual_price) * 2
            print(new_price)

已经有人建议我使用创建新文件了。但是当我想先处理文件中的数据时，这会导致问题。

import csv
import os

  


with open('countries.csv', mode='r') as oldfile, open(
        'countries.tmp', mode='w', newline='') as newfile:
    # define a reader and a writer
    reader = csv.reader(oldfile, delimiter=';', quotechar='"')
    writer = csv.writer(newfile, delimiter=';', quotechar='"',
                        quoting=csv.QUOTE_MINIMAL)
   
    for line in reader: 
       print(*line, sep=';')



    # copy everything changing the third field


    for line in reader:
        if line[2] == "USA":
            actual_price = int(line[2])
            print(actual_price)
            new_price = int(actual_price) * 2
            print(new_price)

    for row in reader:
        writer.writerow([row[0], row[1], ,new_price])


# ok, time to rename the file
os.replace('countries.tmp', 'countries.csv')

感谢您的回答

Answer 1

您在 for 循环的每次迭代中都在更改 new_price。因此，您应该在更改值的循环中写入行：

with open('countries.csv', mode='r') as oldfile, open('countries.tmp', mode='w', newline='') as newfile:
    reader = csv.reader(oldfile, delimiter=';', quotechar='"')
    writer = csv.writer(newfile, delimiter=';', quotechar='"', quoting=csv.QUOTE_MINIMAL)
    for row in reader:
        price = int(row[2])
        if row[1] == "USA":
            price = price*2
        writer.writerow([row[0], row[1], price])

os.replace('countries.tmp', 'countries.csv')

如何在 csv 中仅重写一个字段（行[n]）但同时能够处理数据？

How to rewrite only one field (line[n]) in csv but in same time be able to work with data?

python

csv

csvreader

csvwriter