是否可以使用 csv.DictReader 保持列顺序? [英] Is it possible to keep the column order using csv.DictReader?

问题描述

例如，我的 csv 列如下:

ID, ID2, Date, Job No, Code

我需要以相同的顺序写回列.dict 立即打乱了顺序，所以我认为这更像是读者的问题.

解决方案

Python 的 dict 不维护 3.6 之前的顺序(但无论如何，在那个版本中 csv.DictReader 类被修改为返回 OrderedDicts).

但是，您正在使用的 csv.DictReader 实例(在您阅读第一行之后！-)确实 有一个 .fieldnames 字符串列表，按顺序是.

所以，

 用于 myReader 中的 rowdict:打印 ['%s:%s' % (f, rowdict[f]) for f in myReader.fieldnames]

将向您显示订单确实得到维护(当然在 .fieldnames 中，NEVER 在 dict 中 - 这在本质上是不可能的Python！-).

因此，假设您想以相同的列顺序读取 a.csv 和写入 b.csv.使用普通的读写器太容易了，所以你想改用 Dict 变种；-).嗯，一种方法是...:

导入csva = open('a.csv', 'r')b = open('b.csv', 'w')ra = csv.DictReader(a)wb = csv.DictWriter(b, None)对于 ra 中的 d:如果 wb.fieldnames 是 None:# 初始化并写入 b 的头文件dh = dict((h, h) for h in ra.fieldnames)wb.fieldnames = ra.fieldnameswb.writerow(dh)wb.writerow(d)b.关闭()关闭()

假设您在 a.csv 中有标题(否则您不能在其上使用 DictReader)并且希望 b.csv 中有相同的标题.

For example, my csv has columns as below:

ID, ID2, Date, Job No, Code

I need to write the columns back in the same order. The dict jumbles the order immediately, so I believe it's more of a problem with the reader.

解决方案

Python's dicts do NOT maintain order prior to 3.6 (but, regardless, in that version the csv.DictReader class was modified to return OrderedDicts).

However, the instance of csv.DictReader that you're using (after you've read the first row!-) does have a .fieldnames list of strings, which IS in order.

So,

for rowdict in myReader:
  print ['%s:%s' % (f, rowdict[f]) for f in myReader.fieldnames]

will show you that the order is indeed maintained (in .fieldnames of course, NEVER in the dict -- that's intrinsically impossible in Python!-).

So, suppose you want to read a.csv and write b.csv with the same column order. Using plain reader and writer is too easy, so you want to use the Dict varieties instead;-). Well, one way is...:

import csv

a = open('a.csv', 'r')
b = open('b.csv', 'w')
ra = csv.DictReader(a)
wb = csv.DictWriter(b, None)

for d in ra:

  if wb.fieldnames is None:
    # initialize and write b's headers
    dh = dict((h, h) for h in ra.fieldnames)
    wb.fieldnames = ra.fieldnames
    wb.writerow(dh)

  wb.writerow(d)

b.close()
a.close()

assuming you have headers in a.csv (otherewise you can't use a DictReader on it) and want just the same headers in b.csv.

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