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I've tried many solutions to add a header to my csv file, but nothing's working properly. Here they are :

  1. I used the writerow method, but my data are overwriting the first row.

  2. I used the DictWriter method, but I don't know how to fill it correctly. Here is my code:

    csv = csv.DictWriter(open(directory +'/csv.csv', 'wt'), fieldnames = ["stuff1", "stuff2", "stuff3"], delimiter = ';')
csv.writeheader(["stuff1", "stuff2", "stuff3"])

I got a "2 arguments instead of one" error and I really don't know why.

Any advice?

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2 Answers 2

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25

All you need to do is call DictWriter.writeheader() without arguments:

with open(os.path.join(directory, 'csv.csv'), 'wb') as csvfile:
    writer = csv.DictWriter(csvfile, fieldnames = ["stuff1", "stuff2", "stuff3"], delimiter = ';')
    writer.writeheader()

You already told DictWriter() what your headers are.

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6 Comments

Umm - is t a valid open mode ?
@JonClements: I didn't pay attention to the mode; just copied from the OP. Corrected.
TypeError: 'fieldnames' is an invalid keyword argument for this function, I'm using Python 2.6 , PyQt4.7. Can you help?
@Aleksandar: fieldnames is a keyword argument for the csv.DictWriter() and csv.DictReader() classes only. Make sure you don't confuse this with csv.writer() or csv.reader(). Python 2.6 supports it just fine, if you use it correctly.
@Aleksandar: Right, that Python 2.6 doesn't support. The method was added in Python 2.7. You can simulate it with writer.writerow(dict(zip(writer.fieldnames, writer.fieldnames))).
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I encountered a similar problem when writing the CSV file. I had to read the csv file and modify some of the fields in it. To write the header in the CSV file, i used the following code:

reader = csv.DictReader(open(infile))
headers = reader.fieldnames

with open('ChartData.csv', 'wb') as outcsv:
    writer1 = csv.writer(outcsv)
    writer1.writerow(headers)

and when you write the data rows, you can use a DictWriter in the following way

writer = csv.DictWriter(open("ChartData.csv", 'a' ), headers)

In the above code "a" stands for appending.

In conclusion - > use a to append data to csv after you have written your header to the same file

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1 Comment

Why create a separate csv.writer() first, then open the same file for appending to with a csv.DictWriter()? Just use writer = csv.DictWriter(outcsv, fieldnames=headers), then writer.writeheader().

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