csv module and None values

JKPeck jkpeck at gmail.com
Sat Aug 29 16:12:33 CEST 2009


On Aug 25, 8:49 am, Peter Otten <__pete... at web.de> wrote:
> JKPeck wrote:
> > 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.
>
> How about:
>
> >>> import csv, sys
> >>> class N(int):
>
> ...     def __str__(self): return ""
> ...>>> pseudo_none = N()
> >>> w = csv.writer(sys.stdout, quoting=csv.QUOTE_NONNUMERIC)
> >>> w.writerow([1, "foo", pseudo_none, "bar"])
>
> 1,"foo",,"bar"
>
> Peter

Clever.  Thanks,
Jon



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