Question

I’m writing excel sheets with xlwt, and it’s working great except for one little thing. I would like to display the number zero as a dash (-), the way that it does with accounting. However, I don’t want it to show the dollar sign, $, before everything, and I don’t want it to have commas at the thousands.

I thought this would be a fairly easy problem to solve, I just go and set the format in excel to what I want, then view “Format -> Custom Format” to get the exact format string. Doing so gives me _(* (#,##0);_(* "-"_);_(@_) to use (this doesn’t deal with the commas, but does display zeros as dashes and removes the $).
Unfortunately, when I use that string in xlwt, it seems to reset it to the accounting default: _($* #,##0_);_($* (#,##0);_($* "-"_);_(@_). I think this is a bug in xlwt, but does anyone know if there’s a way around this to let me do what I want to do?

Edit:
Don’t know why it works, but my problem seems to be solved by removing the commas from the string. That is changing:

‘_(* #,##0_);_(* (#,##0);_(* “-“);(@)’
to
‘(* ###0_);_(* (###0);_(* “-“);(@_)’

I believe this works because xlwt doesn’t see it as a custom format when you just remove the $ and instead writes as the accounting default, but when you remove the $ and the commas it kicks it into the custom format method, which is what I want.

In response to John, I’m using these with the tablestyle.numformat attribute. basic code would be:

style = xlwt.xlwt.XFStyle()

style.num_format_str = '_(* ###0_);_(* (###0);_(* "-"_);_(@_)'

The only thing I would ideally like to change now is make negative numbers appear like -5, rather than accounting (5), but I think I can live with how it is now. It might be nice if someone could explain how the excel format strings work though, I can see a bit of rhyme/reason in them but am mostly confused by these long string of numbers that I just cut and paste in.

Answer 1

Here is some minimal working code. In the output spreadsheet, column A is using your original format, B is using what you first appeared to be wanting (accounting format), and column C gives you non-accounting format.

import xlwt
custom_fmts = (
    '_(* (#,##0);_(* "-");(@)',
    '_(#0_);(#0);"-"_)', # positive;negative;zero
    '#0;-#0;"-"', # positive;negative;zero
    )
xfs = [xlwt.easyxf('', fmt) for fmt in custom_fmts]
wb = xlwt.Workbook()
ws = wb.add_sheet('x')
for colx, xf in enumerate(xfs):
    for rowx, value in enumerate((1234567, 0, -1234567)):
        ws.write(rowx, colx, value, xf)

wb.save('demo_custom_format.xls') 

You may like to read the tutorial that you can access via this link.

It might be nice if someone could explain how the excel format strings
work

No good telling you to RTFM because there hasn’t been a manual since about Excel 5.0 AFAIK but you can always HTF1K (hit the F1 key) then type custom formats into the search box and then FYN (follow your nose).