csv.DictWriter - 类型错误：__init __（）至少需要3个参数（假设4） [英] csv.DictWriter -- TypeError: __init__() takes at least 3 arguments (4 given)

问题描述

我试着写字典的CSV列表时遇到问题初始化 csv.DictWriter（）。我有：

I'm trying to write a list of dictionaries to a CSV and am having issues initializing csv.DictWriter(). I've got:

fname = "Machine Detection Rate.csv"
with open(fname, "wb") as f:
    fieldNames = ["Number of Packets", "Number of Machines"]
    writer = csv.DictWriter(f, fieldNames=fieldNames, restval="", dialect="excel",)
    writer.writeheader()
    for line in machineCounter:
        print "Got Here!"
        writer.writerow(line)

我得到的错误是：

The error I get is:

TypeError: __init__() takes at least 3 arguments (4 given)

我试过的参数各种排列，但似乎并没有能够得到它运行。我也似乎没有能够找到任何人谁是有问题的。我没有尝试过指定的唯一参数是 * ARGS 和 ** kwds 。我是一个小白依然，尽管读书，我不明白他们在这种情况下如何工作的。任何想法？

I've tried various permutations of arguments, but don't seem to be able to get it to run. I also don't seem to be able to find anyone else who's had the problem. The only arguments I haven't tried specifying are *args and **kwds. I'm a noob still and despite reading, I don't understand how they work in this situation. Any ideas?

编辑：在最后的为循环我有 writer.writerows（）里面也没有输出的全部类型的字典在列表中。更改为 writer.writerow（）。

in the final for loop I had writer.writerows() which did not output the all the dicts in the list. Changed to writer.writerow().

推荐答案

该参数的名称是字段名（全部小写），而不是字段名：

The name of the parameter is fieldnames (all lowercase), not fieldNames:

writer = csv.DictWriter(f, fieldnames=fieldNames, restval="", dialect="excel",)

演示：

>>> import csv
>>>
>>> with open('test.csv') as f:
...     fieldnames = ["Number of Packets", "Number of Machines"]
...     writer = csv.DictWriter(f, fieldNames=fieldnames, restval="", dialect="excel",)
...
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
TypeError: __init__() takes at least 3 arguments (4 given)
>>>
>>> with open('test.csv') as f:
...     fieldNames = ["Number of Packets", "Number of Machines"]
...     writer = csv.DictWriter(f, fieldnames=fieldNames, restval="", dialect="excel",)
...
>>> writer
<csv.DictWriter instance at 0x01AD8E90>
>>>

请注意，Python没有一个错误，如抱怨：

Note that Python doesn't complain with an error such as:

类型错误：DictWriter得到了一个意外的关键字参数的字段名

由于 csv.DictWriter 恰好有一个 ** kwds 参数。你可以看到它在文档如果你看一下签名

because csv.DictWriter happens to have a **kwds parameter. You can see it in the documentation if you look at the signature:

类csv.DictWriter（csvfile，字段名，restval =''，extrasaction ='加薪'，方言='Excel的'，* ARGS，** kwds）

这个参数将接受任意数量的关键字参数。

This parameter will accept any number of keyword arguments.

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