Formatting chart data labels in openpyxl

Question

I'm using Python 3.6.3 to write some excel sheets with openpyxl (2.4.9). Getting data labels on charted data wasn't obvious, but things start to go badly when I try to format said data labels. What I want to be able to do is change their position and also change their rotation. Anyone any ideas? I'm a bit fresh to python, so any advice would be great. Here's what I've tried:

from openpyxl.chart import LineChart, Reference, Series
from openpyxl.chart.label import DataLabelList
from openpyxl.chart.text import RichText
from openpyxl.drawing.text import RichTextProperties

#this is the only way I found to set text properties which didnt give an error
vertical = RichTextProperties(rot = 270)
labelvertical = RichText(bodyPr = vertical)


chart1 = LineChart()

# setup and append the first series
values = Reference(dprsheet, min_col=5, min_row=4, max_row=34)
series = Series(values, title="Series 1")
chart1.append(series)

# setup and append the second series
values = Reference(dprsheet, min_col=8, min_row=4, max_row=34)
series = Series(values, title="Series 2")
chart1.append(series)

dates = Reference(dprsheet, min_col=2, min_row=4, max_row=34)

chart1.set_categories(dates)

s1 = chart1.series[0]
s1.graphicalProperties.line.solidFill = 'FF0000'
s1.graphicalProperties.line.width = 25000
s1.dLbls = DataLabelList() 
s1.dLbls.showVal = True

## s1.dLbls.dLblPos = 't'
## if ^this^ line isn't commented then ALL images in the sheet are removed by excel upon opening
## s1.dLbls.txPr = labelvertical
## if ^this^ line isn't commented then ALL images in the sheet are removed by excel upon opening
s2 = chart1.series[1]
s2.graphicalProperties.line.solidFill = '000000'
s2.graphicalProperties.line.width = 25000

essheet.add_chart(chart1, 'B35')

Answer 1

I got there in the end, via trying to work out how to change the axis labels... this should be extendable to any changes (using either the paragraph properties for fonts etc, or body properties for alignment etc).

from openpyxl.chart import LineChart, Reference, Series
from openpyxl.chart.label import DataLabelList
from openpyxl.chart.text import RichText
#additional imports needed for the solution:
from openpyxl.drawing.text import Paragraph, ParagraphProperties, CharacterProperties

chart1 = LineChart()
# setup and append the first series
values = Reference(dprsheet, min_col=5, min_row=4, max_row=34)
series = Series(values, title="Series 1")
chart1.append(series)
# setup and append the second series
values = Reference(dprsheet, min_col=8, min_row=4, max_row=34)
series = Series(values, title="Series 2")
chart1.append(series)

dates = Reference(dprsheet, min_col=2, min_row=4, max_row=34)
chart1.set_categories(dates)

#create label styling
axis = CharacterProperties(sz=800)
rot = openpyxl.drawing.text.RichTextProperties(vert='vert270')

#set axis label styles
chart1.x_axis.txPr = RichText(p=[Paragraph(pPr=ParagraphProperties(defRPr=axis), endParaRPr=axis)], bodyPr=rot)
chart1.y_axis.txPr = RichText(p=[Paragraph(pPr=ParagraphProperties(defRPr=axis), endParaRPr=axis)])

#set data labels and styles
s1 = chart1.series[0]
s1.dLbls = DataLabelList() 
s1.dLbls.showVal = True
s1.dLbls.txPr = RichText(p=[Paragraph(pPr=ParagraphProperties(defRPr=axis), endParaRPr=axis)], bodyPr=rot)

Note that chart.dataLabels.dLblPos still does not work (txPr can be amended but not position). The obvious work around requires setting position on each series individually.

Answer 2

Sorry, but I'm afraid you're hitting the limitations of the OOXML specification which isn't always very clear on this stuff. Essentially, at this level openpyxl exposes the XML schema to Python so you're best having a copy of the specification to hand along with a comparable file created by Excel to see what it does.

For an example of the kind of thing that is undocumented: if you want chartlines to have different colour you must have lumOff before lumMod in the relevant part of DrawingML.

We're never going to be able to document all this in openpyxl.