替换格式为 csv 行的字符串中的项目

Question

目标是以优雅的方式将csv_line 的第二个字段替换为new_item。这个问题与 Rawing 列出的主题不同，因为我们在这里使用不同的数据结构，尽管我们可以使用其他主题来获得启发。

# Please assume that csv_line has not been imported from a file.
csv_line = 'unknown_item1,unknown_old_item2,unknown_item3'
new_item = 'unknown_new_item2'
goal = 'unknown_item1,unknown_new_item2,unknown_item3'

# Works but error prone. Non-replaced items could be inadvertently swapped.
# In addition, not convenient if string has many fields.
item1, item2, item3 = csv_line.split(',')
result = ','.join([item1, new_item, item3])
print(result)  # unknown_item1,unknown_new_item2,unknown_item3

# Less error prone but ugly.
result_list = []
new_item_idx = 1
for i, item in enumerate(csv_line.split(',')):
    result_list += [item] if i != new_item_idx else [new_item]
result = ','.join(result_list)
print(result)  # unknown_item1,unknown_new_item2,unknown_item3

# Ideal (not-error prone) but not working.
csv_line.split(',')[1] = new_item
print(csv_line)  # unknown_item1,unknown_old_item2,unknown_item3

Answer 1

可以使用 Python 的 CSV 库通过使用 io.StringIO() 对象来替换第二项。这表现得像文件，但可以作为字符串读取：

import csv
import io

csv_line = 'unknown_item1,unknown_old_item2,unknown_item3'
new_item = 'unknown_new_item2'

row = next(csv.reader(io.StringIO(csv_line)))
row[1] = new_item
output = io.StringIO()
csv.writer(output).writerow(row)
goal = output.getvalue()

print(goal)

这会将goal 显示为：

unknown_item1,unknown_new_item2,unknown_item3

Answer 2

这似乎是最pythonic：

csv_line = 'unknown_item1,old_item2,unknown_item3'
old_index = 1
new_item = 'new_item2'
goal = 'unknown_item1,new_item2,unknown_item3'

items = csv_line.split(',')
items[old_index] = new_item

print(','.join(items))
print(goal)

输出：

unknown_item1,new_item2,unknown_item3
unknown_item1,new_item2,unknown_item3

Answer 3

在csv_line.split(',')[1] = new_item 行中，您根本不更改 csv_line 变量。您需要先将使用 .split() 创建的新列表分配给变量，然后才能更改其中的元素：

new_csv = csv_line.split(',')
new_csv[1] = new_item

print(','.join(new_csv))

Answer 4

l = csv_line.split(',')
l[1] = new_item
csv_line = ','.join(l)