Python csv.DictReader。 阅读 alter dictionary 然后 output 到文件

Question

我需要读入 pipe 分隔文件更改一些字段和 output。它读起来很好，我可以更改列。 writer 部分写入 header 但 writerows 不写入任何内容。 我怎样才能output更新内容？

csv.register_dialect('pipe',delimiter='|', quoting=csv,QUOTE_NONE)

with open('test.txt') as csvfile
    cfile=csv.DictReader(cfile,dialect='pipe')
    fieldnames=cfile.fieldnames
    for row in cfile:
        row['address']=scrubrow(row['address']
    

    with open('c.txt','w') as outfile:
        writer=csv.DictWriter(outfile,fieldnames=fieldnames,dialect='pipe')
        writer.writeheader()
        writer.writerows(cfile)

Answer 1

cfile是一个空迭代器。 你丢弃了除最后row以外的所有内容，所以row['address']=scrubrow(row['address']实际上没有做任何事情。

执行此操作的简单方法是创建一个列表并使用该列表：

csv.register_dialect('pipe',delimiter='|', quoting=csv,QUOTE_NONE)

with open('test.txt') as csvfile
    reader = csv.DictReader(cfile, dialect='pipe')
    fieldnames = cfile.fieldnames
    rows = []
    for row in reader:
        rows.append(scrubrow(row['address']))
    
    with open('c.txt','w') as outfile:
        writer = csv.DictWriter(outfile, fieldnames=fieldnames, dialect='pipe')
        writer.writeheader()
        writer.writerows(rows)

但这将是低效的，因为它需要 O(N) 空间。 相反，一次只保留 memory 中的一行，您可以这样做：

csv.register_dialect('pipe',delimiter='|', quoting=csv,QUOTE_NONE)

with open('test.txt') as csvfile, open('c.txt','w') as outfile:
    reader = csv.DictReader(cfile,dialect='pipe')

    fieldnames = reader.fieldnames
    writer = csv.DictWriter(outfile,fieldnames=fieldnames,dialect='pipe')

    writer.writeheader()
    for row in reader:
        writer.writerow(scrubrow(row['address']))