How to apply conditional formatting in openpyxl?

Question

I am using openpyxl to manipulate a Microsoft Excel Worksheet.

What I want to do is to add a Conditional Formatting Rule that fills the rows with a given colour if the row number is even, leaves the row blank if not.

In Excel this can be done by selecting all the worksheet, creating a new formatting rule with the text =MOD(ROW();2)=0 or =EVEN(ROW()) = ROW() .

I tried to implement this behaviour with the following lines of code (considering for example the first 10 rows):

redFill = PatternFill(start_color='EE1111', end_color='EE1111', fill_type='solid')
ws2.conditional_formatting.add('A1:A10', FormulaRule(formula=['MOD(ROW();2) = 0'], stopIfTrue=False, fill=redFill))

My program runs correctly but when I try to open the output Excel file, it tells me that the file contains unreadable content and it asks me if I want to recover the worksheet content. By clicking yes, the worksheet is what I expect but there is no formatting.

What is the correct way to apply such a formatting in openpyxl (possibly to the entire worksheet)?

Answer 1

Unfortunately, the way formulae are handled in conditional formatting is particularly opaque. The best thing to do is to create a file with the relevant conditional format and inspect the relevant file by unzipping it. The rules are stored in the relevant worksheet files and the formats in the styles file.

However, I suspect that the problem may simply because you are using ";" to separate parameters in the function: you must always use commas for this.

A sample formula from one of my projects:

green_text = Font(color="006100")
green_fill = PatternFill(bgColor="C6EFCE")
dxf2 = DifferentialStyle(font=green_text, fill=green_fill)
r3 = Rule(type="expression", dxf=dxf2)
r3.formula = ["AND(ISNUMBER(C2), C2>=400)"]