使用DictWriter编写字典键的子集 [英] Using DictWriter to write a subset of a dictionary's keys

问题描述

我编写了一个函数，该函数使用csv模块将字典列表序列化为CSV文件，其代码如下:

I wrote a function that serializes a list of dictionaries as a CSV file using the csv module, with code like this:

data = csv.DictWriter(out_f, fieldnames)
data.writerows(dictrows)

但是，有时我只想将每个字典键的一个子集写到文件中.如果我以fieldnames的形式传递每个字典具有的键的子集，则会收到错误消息:

However, I sometimes want to write out to a file only a subset of each dictionary's keys. If I pass as fieldnames a subset of the keys that each dictionary has, I get the error:

"dict contains fields not in fieldnames"

如何做到这一点，以便DictRows仅将我指定的字段的子集写入CSV，而忽略字典中但字段名中没有的那些字段?

How can I make it so that DictRows will write just a subset of the fields I specify to CSV, ignoring those fields that are in the dictionary but not in fieldnames?

推荐答案

最简单，最直接的方法是在初始化DictWriter实例时通过extrasaction='ignore'，如

Simplest and most direct approach is to pass extrasaction='ignore' when you initialize your DictWriter instance, as documented here:

如果字典传递给 writerow()方法包含的密钥不 在字段名称中找到，可选 extrasaction参数指示什么 采取的行动.如果设置为 'raise'出现ValueError.如果它 设置为'ignore'，其中的额外值 字典被忽略了.

If the dictionary passed to the writerow() method contains a key not found in fieldnames, the optional extrasaction parameter indicates what action to take. If it is set to 'raise' a ValueError is raised. If it is set to 'ignore', extra values in the dictionary are ignored.

它也可以在writerows上运行，在内部，它只是重复调用writerow.

It also works on writerows, which, internally, just calls writerow repeatedly.

这篇关于使用DictWriter编写字典键的子集的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！