How to automate Excel report generation with Python?

First, let's understand the prerequisites. You will need to have Python installed on your computer. Then, you should have packages such as pandas and xlsxwriter installed. To install these packages, you can use pip (a package installer for Python). In your terminal, type:

pip install pandas xlsxwriter

Now, let's dive into how to automate Excel report generation with Python. We'll use a hypothetical sales report, which includes calculations such as totals and percentages.

Step 1: Importing required libraries

import pandas as pd

Here, we import pandas, a library offering data structures and operations for manipulating numerical tables and time series.

Step 2: Preparing the data

Load the data from an existing .csv or .xlsx file or prepare the data manually.

# Loading data from a .csv file
df = pd.read_csv('sales.csv')

# Same can be done for .xlsx file
# df = pd.read_excel('sales.xlsx')

Now, let's assume that our DataFrame df looks like this:

Step 3: Perform necessary calculations

For example, let's calculate total units sold, total revenue and revenue percentage for each product.

total_units = df['units'].sum()
total_revenue = df['revenue'].sum()

df['revenue_percentage'] = df['revenue']/total_revenue * 100

Step 4: Create a new Excel writer object

writer = pd.ExcelWriter('sales_report.xlsx', engine='xlsxwriter')

Here, we create a new Excel file named 'sales_report.xlsx' through the ExcelWriter object of pandas.

Step 5: Write data to Excel file

df.to_excel(writer, sheet_name = 'Sales Report', index = False)

Step 6: Apply formatting

xlsxwriter allows you to format your Excel files. For instance, you can add charts, colors, fonts etc.

# Get xlsxwriter objects
workbook  = writer.book
worksheet = writer.sheets['Sales Report']

# Add a header format
header_format = workbook.add_format({
    'bold': True,
    'text_wrap': True,
    'valign': 'top',
    'fg_color': '#D7E4BC', 
    'border': 1})

# Write column headers with defined format
for col_num, value in enumerate(df.columns.values):
    worksheet.write(0, col_num, value, header_format)

# Add a chart
chart = workbook.add_chart({'type': 'column'})

# Configure the chart from the dataframe data, 
# using the first column for x, and second column for values
chart.add_series({'values': '=Sales Report!$D$2:$D$'+str(len(df)+1),
                  'categories': '=Sales Report!$A$2:$A$'+str(len(df)+1),
                  'name': "Sales",
                  })

worksheet.insert_chart('F2', chart)

Step 7: Save and close the Excel writer

writer.save()

In conclusion, the Python libraries pandas and xlsxwriter are powerful tools that can help to automatically generate an Excel report. We can manipulate data with pandas, and then format, organize, and write data to an Excel file with xlsxwriter. For more complex reports, remember that xlsxwriter can be used to add charts, images, and even formulas to Excel files.