如何使用csv.DictWriter编写标题行? [英] How to write header row with csv.DictWriter?

问题描述

假设我有一个csv.DictReader对象，我想将其写为CSV文件.我该怎么办?

Assume I have a csv.DictReader object and I want to write it out as a CSV file. How can I do this?

我知道我可以这样写行数据:

dr = csv.DictReader(open(f), delimiter='\t')
# process my dr object
# ...
# write out object
output = csv.DictWriter(open(f2, 'w'), delimiter='\t')
for item in dr:
    output.writerow(item)

但是如何包含字段名?

推荐答案

在2.7/3.2中，有新的writeheader()方法.同样，约翰·马钦(John Machin)的答案提供了一种更简单的写标题行的方法.
现在在2.7/3.2中提供了使用writeheader()方法的简单示例:

In 2.7 / 3.2 there is a new writeheader() method. Also, John Machin's answer provides a simpler method of writing the header row.
Simple example of using the writeheader() method now available in 2.7 / 3.2:

from collections import OrderedDict
ordered_fieldnames = OrderedDict([('field1',None),('field2',None)])
with open(outfile,'wb') as fou:
    dw = csv.DictWriter(fou, delimiter='\t', fieldnames=ordered_fieldnames)
    dw.writeheader()
    # continue on to write data

---

实例化DictWriter需要一个fieldnames参数.
来自文档:

---

Instantiating DictWriter requires a fieldnames argument.
From the documentation:

fieldnames参数标识 值在其中的顺序 传递给writerow()的字典 方法被写入到csvfile中.

The fieldnames parameter identifies the order in which values in the dictionary passed to the writerow() method are written to the csvfile.

以另一种方式:因为Python字典本质上是无序的，所以需要Fieldnames参数.
以下是如何将标头和数据写入文件的示例.
注意:with语句是在2.6中添加的.如果使用2.5:from __future__ import with_statement

Put another way: The Fieldnames argument is required because Python dicts are inherently unordered.
Below is an example of how you'd write the header and data to a file.
Note: with statement was added in 2.6. If using 2.5: from __future__ import with_statement

with open(infile,'rb') as fin:
    dr = csv.DictReader(fin, delimiter='\t')

# dr.fieldnames contains values from first row of `f`.
with open(outfile,'wb') as fou:
    dw = csv.DictWriter(fou, delimiter='\t', fieldnames=dr.fieldnames)
    headers = {} 
    for n in dw.fieldnames:
        headers[n] = n
    dw.writerow(headers)
    for row in dr:
        dw.writerow(row)

正如@FM在评论中提到的那样，您可以将标头编写压缩为单行代码，例如:

As @FM mentions in a comment, you can condense header-writing to a one-liner, e.g.:

with open(outfile,'wb') as fou:
    dw = csv.DictWriter(fou, delimiter='\t', fieldnames=dr.fieldnames)
    dw.writerow(dict((fn,fn) for fn in dr.fieldnames))
    for row in dr:
        dw.writerow(row)

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