Understanding Pandas and OpenPyXL: A Deep Dive into Excel Formatting Issues

Introduction

The world of data analysis and manipulation is vast and complex, with various libraries and tools at our disposal to achieve our goals. Two such popular libraries are pandas for data manipulation and openpyxl for creating and editing excel files. In this article, we’ll delve into a common issue that can arise when using pandas and openpyxl: formatting problems.

Background

Pandas is an excellent library for data manipulation and analysis, providing data structures and functions to efficiently handle large datasets. One of its strengths is the ability to easily manipulate and format data, making it ideal for data scientists and analysts. On the other hand, openpyxl is a powerful library for creating and editing excel files, offering a wide range of features and options.

The Problem: Styling Pandas DataFrames with OpenPyXL

When working with pandas DataFrames, it’s not uncommon to want to add some visual flair or styling to our data. This can include formatting columns, adding borders, or even creating bar charts. However, when using openpyxl to save these styled DataFrames as excel files, we often encounter issues.

In this article, we’ll explore a specific issue that has been reported in the Stack Overflow community: pandas and openpyxl formatting not working. We’ll examine the code, the libraries involved, and provide solutions to get you back on track with your data analysis and manipulation tasks.

The Code

Let’s take a closer look at the code snippet provided in the question:

styled_df = df.style.bar(['Null_Percentage'], color="#bbddbb")
styled_df.to_excel(path, engine='openpyxl', encoding='utf-8', index=False)

Here, we’re using the pandas style function to apply styling to a specific column in our DataFrame. The bar function creates a bar chart for that column, and the color parameter sets the color of the bars.

We then call the to_excel method on the styled DataFrame to save it as an excel file using openpyxl.

Issues with OpenPyXL

The issue arises when we try to save the styled DataFrame as an excel file using openpyxl. The formatting applied by pandas using the style function seems to be ignored, resulting in a plain excel file without any visual styling.

To understand why this happens, let’s take a closer look at how openpyxl works with pandas DataFrames.

How OpenPyXL Interacts with Pandas

When you use the to_excel method on a pandas DataFrame, it creates an excel file using openpyxl. The engine='openpyxl' parameter tells pandas to use openpyxl for creating and editing excel files.

However, when it comes to styling DataFrames, pandas uses its own internal formatting mechanisms rather than relying directly on openpyxl’s styling capabilities. This means that any formatting applied by pandas is not automatically propagated to the excel file created using openpyxl.

Solutions

Fortunately, there are a few workarounds to get around this issue:

1. Use OpenPyXL Styling Directly

One way to achieve desired formatting is to use openpyxl’s styling capabilities directly in your code. Here’s an example:

from openpyxl import Workbook

# Create a new workbook using openpyxl
wb = Workbook()

# Select the first sheet
ws = wb.active

# Set the header row
ws['A1'] = 'Null Percentage'
ws['B1'] = 'Value'

# Add some data to the worksheet
for i in range(10):
    ws.cell(row=i+2, column=1).value = (i/100)*100
    ws.cell(row=i+2, column=2).value = (i/100)*100

# Set the bar colors using openpyxl's styling capabilities
from openpyxl.styles import PatternFill
ws['A2'].fill = PatternFill(fgColor="#bbddbb", fill_type='solid')
ws['B2'].fill = PatternFill(fgColor="#bbddbb", fill_type='solid')

# Save the workbook to a file
wb.save('styled_excel.xlsx')

In this example, we create a new workbook using openpyxl and select the first sheet. We then set some header text and data in the worksheet.

Finally, we use openpyxl’s styling capabilities to apply bar colors to specific cells in the worksheet.

2. Use Pandas’ Styling with OpenPyXL

Another way to achieve desired formatting is to use pandas’ styling capabilities along with openpyxl’s styling capabilities. Here’s an example:

import pandas as pd
from openpyxl import Workbook, styles

# Create a new DataFrame
df = pd.DataFrame({
    'Null_Percentage': [1, 2, 3],
    'Value': [10, 20, 30]
})

# Apply styling to the DataFrame using pandas' styling capabilities
styled_df = df.style.bar(['Null_Percentage'], color="#bbddbb")

# Save the styled DataFrame as an excel file using openpyxl's styling capabilities
with pd.ExcelWriter('styled_excel.xlsx', engine='openpyxl') as writer:
    styled_df.to_excel(writer, sheet_name='Sheet1', index=False)

In this example, we create a new DataFrame and apply styling to it using pandas’ style function.

We then save the styled DataFrame as an excel file using openpyxl’s ExcelWriter class, which allows us to specify the style for the excel file.

Last modified on 2024-12-11