Python csv.DictWriter writerow（）返回错误

Question

I'm trying to manipulate a csv file using Python's csv package. I want to open the csv file, manipulate it (clean it from certain artefacts), write the changes to another file, done.

I'm having troubles with the writing part. I'm not sure whether I'm using the csv.DictWriter correctly. The last line of my code produces the error:

TypeError: init () takes at least 3 arguments (2 given)

Why am I getting this error?

import csv


dataSource = 'dentistData.csv'
dataTarget = 'test.csv'

with open(dataSource) as source, open(dataTarget) as target:

    reader = csv.DictReader(source, delimiter=",", quotechar='"')
    writer = csv.DictWriter(target, delimiter=',')

    for row in reader:

        #if dentist_type is empty, add the type PRV (private dentist)
        if not row['dentist_type']:
            row['dentist_type']='PRV'
        print(row['dentist_type'])

        #remove lgh from street field
        writer.writerow(row)

Answer 1

You are missing the mandatory parameter fieldnames of [csv.DictWriter](https://docs.python.org/2/library/csv.html#csv.DictWriter) .

The fieldnames parameter is a sequence of keys that identify the order in which values in the dictionary passed to the writerow() method are written to the csvfile.

Note that unlike the DictReader class, the fieldnames parameter of the DictWriter is not optional. Since Python's dict objects are not ordered, there is not enough information available to deduce the order in which the row should be written to the csvfile.

The complete signature is:

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

Example from doc:

import csv

with open('names.csv', 'w') as csvfile:
    fieldnames = ['first_name', 'last_name']
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

    writer.writeheader()
    writer.writerow({'first_name': 'Baked', 'last_name': 'Beans'})
    writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})
    writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})