How to format all cells in one sheet based on corresponding cell values in another sheet using XlsxWriter?

Question

I am exporting to Excel two pandas DataFrames using XlsxWriter, each DataFrame having a separate sheet. I would like to apply a colour format to all the cells in one sheet based on values in another sheet, they correspond one-to-one based on column names and row numbers.

Example:

Sheet1

  A B C
1 1 3 1
2 0 4 2

Sheet2

  A B C
1 a d b
2 b a a

I would like to assign a colour format to all the cells in Sheet1 that have a value 'a' in Sheet2.

Answer 1

The first step is to work out the conditional format in Excel and then transfer it to XlsxWriter.

Something like the following should work:

import pandas as pd

# Create some Pandas dataframes from some data.
df1 = pd.DataFrame([[ 1,   3,   1 ], [ 0,   4,   2 ]])
df2 = pd.DataFrame([['a', 'd', 'b'], ['b', 'a', 'a']])

# Create a Pandas Excel writer using XlsxWriter as the engine.
writer = pd.ExcelWriter('pandas_xlsxwriter.xlsx', engine='xlsxwriter')

# Write each dataframe to a different worksheet.
df1.to_excel(writer, sheet_name='Sheet1', header=False, index=False)
df2.to_excel(writer, sheet_name='Sheet2', header=False, index=False)

# Get the xlsxwriter workbook and worksheet objects.
workbook  = writer.book
worksheet = writer.sheets['Sheet1']

# Create a format for the conditional format.
condition_format = workbook.add_format({'bg_color': '#C6EFCE',
                                        'font_color': '#006100'})

# Write a conditional format over a range.
worksheet.conditional_format('A1:C2', {'type': 'formula',
                                       'criteria': '=Sheet2!A1="a"', 
                                       'format': condition_format})

# Close the Pandas Excel writer and output the Excel file.
writer.save()

Output:

Note that Excel requires double quotes around the string in the formula =Sheet2!A1="a" and by using a relative cell reference ( A1 not the absolute value $A$1 ) the formula is applied individually to each cell in the range.

You can apply the conditional format to a range based on the dataframe like this:

# Write a conditional format over a range.
start_row = 0
start_col = 0
end_row = df1.shape[0] -1
end_col = df1.shape[1] -1

worksheet.conditional_format(start_row, start_col, end_row, end_col, 
                             {'type': 'formula',
                              'criteria': '=Sheet2!A1="a"', 
                              'format': condition_format})