csv module and None values

JKPeck jkpeck at gmail.com
Tue Aug 25 16:02:36 CEST 2009

On Aug 24, 10:43 pm, John Yeung <gallium.arsen... at gmail.com> wrote:
> On Aug 24, 5:00 pm, Peter Otten <__pete... at web.de> wrote:
> > If I understand you correctly the csv.writer already does
> > what you want:
> > >>> w.writerow([1,None,2])
> > 1,,2
> > just sequential commas, but that is the special treatment.
> > Without it the None value would be converted to a string
> > and the line would look like this one:
> > 1,None,2
> No, I think he means he is getting
> >>> w.writerow([1,None,2])
> 1,"",2
> He evidently wants to quote "all" strings, but doesn't want None to be
> considered a string.
> John

Exactly so.  The requirement of the receiving program, which is out of
my control, is that all strings be quoted but a None in a numeric
field result in the ,, output rather than "".  Excel quotes strings
conditionally, which doesn't do what is needed in this case.  For
QUOTE_NONNUMERIC to quote None values makes some sense, but it gets in
the way of representing missing values in a numeric field.  It would
be nice to have a choice here in the dialects.

I thought of replacing the None values with float(nan), since that has
a numeric type, but unfortunately that results in writing the string
(unquoted) nan for the value.  So the sentinel approach seems to be
the best I can do.


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