1

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)

The error I get is:

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

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?

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

Jim
  • 73
  • 1
  • 7

1 Answers1

3

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

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

Demo:

>>> 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>
>>>

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

TypeError: DictWriter got an unexpected keyword argument 'fieldNames'

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

class csv.DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)

This parameter will accept any number of keyword arguments.