Writing Custom Formatted Headers in xlsxwriter

In this article, we’ll delve into the world of Python’s xlsxwriter library, which allows us to create Excel files programmatically. We’ll explore how to left align a single row using xlsxwriter, and provide an alternative approach to formatting headers.

Introduction to xlsxwriter

xlsxwriter is a powerful Python library that enables you to create Excel files (.xlsx) with ease. It’s built on top of the pandas data manipulation library, making it easy to integrate with your existing workflows. With xlsxwriter, you can write custom formatted headers, footers, and even entire sheets.

Understanding Pandas’ Auto-Header

Before we dive into custom formatting, let’s take a look at how pandas handles its own header format. When using the to_excel() method from pandas, it writes the dataframe header with a default cell format, which cannot be overridden directly using the set_row() method.

import pandas as pd

# Sample dataframe
stats = pd.DataFrame({
    'Column A': [1, 2, 3],
    'Column B': [4, 5, 6]
})

# Create an Excel writer object
xl_writer = pd.ExcelWriter('test.xlsx')

# Write the dataframe to the Excel file
stats.to_excel(xl_writer, 'Stats')

# Load the workbook and sheet
import xlsxwriter
workbook = xl_writer.book
sheet = workbook.add_worksheet()

# Attempting to set a row format directly will fail
# stats_sheet.set_row(0, None, {'align': 'left'})

Turning Off Pandas’ Auto-Header and Writing Custom Format

To achieve custom formatting, we need to turn off the automatic header from pandas using the to_excel() method’s index parameter. Then, we can use xlsxwriter to write our own formatted header.

import pandas as pd
from xlsxwriter import Workbook

# Sample dataframe
stats = pd.DataFrame({
    'Column A': [1, 2, 3],
    'Column B': [4, 5, 6]
})

# Turn off the auto-header and write a custom format header
workbook = Workbook('test.xlsx')
ws = workbook.add_worksheet()
stats.write(0, 0, 'Left Aligned Header')
for i in range(len(stats.columns)):
    ws.set_column(i, i, 20) # set column width to 20 characters

# Close the workbook to save it
workbook.close()

import xlsxwriter
with Workbook('test.xlsx', { 'features': {'sorted_xy': True} }) as workbook:
    worksheet = workbook.add_worksheet()
    
    stats.write(0, 0, 'Left Aligned Header')
    for i in range(len(stats.columns)):
        worksheet.set_column(i, i, 20) # set column width to 20 characters

# Now we can use xlsxwriter's row formatting
import xlsxwriter
with Workbook('test.xlsx', { 'features': {'sorted_xy': True} }) as workbook:
    ws = workbook.add_worksheet()
    
    format_header = {
        "bold": True,
        "align": ("left",),  # left align the text
        "font": [
            {"name": "Arial", "size": 14},
            {"name": "Courier New", "size": 12}
        ],
        "bg_color": "#C9E4CA"  # light green background
    }
    
    stats.write(0, 0, 'Left Aligned Header')
    for i in range(len(stats.columns)):
        ws.set_column(i, i, 20) # set column width to 20 characters
    
    format_header_row = {
        "bold": True,
        "align": ("left",),  # left align the text
        "font": [
            {"name": "Arial", "size": 14},
            {"name": "Courier New", "size": 12}
        ],
        "bg_color": "#C9E4CA"  # light green background
    }
    
    stats.write(0, 1, 'Another Column', format_header_row)

Using `xlsxwriter`’s Row Formatting

As shown above, we can use the set_column() method to set the column width and set_cell() with a dictionary to write custom formatted headers. We can define the header format in the same way as for columns.

format_header_row = {
    "bold": True,
    "align": ("left",),  # left align the text
    "font": [
        {"name": "Arial", "size": 14},
        {"name": "Courier New", "size": 12}
    ],
    "bg_color": "#C9E4CA"  # light green background
}

# writing custom header for column using format_header_row:
stats.write(0, 1, 'Another Column', format_header_row)

Conclusion

In this article, we explored how to left align a single row in an Excel file created with xlsxwriter. We learned that pandas handles its own headers automatically and cannot be overridden directly using the set_row() method. Instead, we turned off the automatic header from pandas and used xlsxwriter to write our own formatted header.

By turning off the pandas auto-header and writing custom formats for columns or rows with xlsxwriter, you can achieve precise control over your Excel file’s formatting.

Last modified on 2023-08-10