name 'ExcelWriter' is not defined

This error message suggests that the program is trying to use the name 'ExcelWriter' but it has not been defined or imported properly.

To fix the issue, make sure that you have imported the necessary library or module that contains the 'ExcelWriter' class. For example, if you are using the Pandas library for data analysis, you need to import the 'pandas' and 'openpyxl' modules.

Here's an example code snippet that demonstrates how to create an Excel file using the Pandas library:

import pandas as pd

# create a sample dataframe
data = {'Name': ['John', 'Mary', 'Peter', 'Jane'],
        'Age': [25, 30, 35, 40]}
df = pd.DataFrame(data)

# create a new Excel file and write the dataframe to a sheet
writer = pd.ExcelWriter('output.xlsx', engine='openpyxl')
df.to_excel(writer, sheet_name='Sheet1', index=False)
writer.save()

In this example, we use the 'ExcelWriter' class from the 'pandas' library to create a new Excel file called 'output.xlsx' and write a dataframe to a sheet named 'Sheet1'. We also specify the 'openpyxl' engine to ensure compatibility with Excel files created in newer versions of Excel.