Hey there! Let's dig into why your openpyxl-generated workbook is throwing that frustrating error when you try to open it. Since you're pulling data from MongoDB and writing to Excel, here are the most common culprits to check, along with fixes tailored to your use case:

1. Unsupported MongoDB Data Types in Cells #

MongoDB’s flexible schema includes types that Excel doesn’t handle natively—think ObjectId, timezone-aware datetimes, nested documents, or binary data. Writing these raw values directly to cells can break the workbook structure.

• Fix: Convert all non-Excel-friendly types first:
  • Cast ObjectId to string: str(document["_id"])
  • Strip timezones from datetimes: document["created_at"].replace(tzinfo=None) or format as a string: document["created_at"].isoformat()
  • Flatten nested documents into separate columns, or serialize them to JSON strings if you need to preserve structure

2. Unclosed File Handles or Improper Saving #

If you don’t properly save and close the workbook object, Excel can’t read the incomplete file data. This is a super common oversight!

• Fix: Use a with context manager to ensure automatic cleanup (this is the safest approach):

from openpyxl import Workbook

with Workbook() as wb:
    ws = wb.active
    # Write your MongoDB data to the worksheet here
    wb.save("mongo_data.xlsx")

If you’re not using a context manager, explicitly call wb.close() right after saving the file.

3. Invalid Characters in Sheet Names or Cell Values #

Excel has strict rules:

• Sheet names can’t exceed 31 characters, and can’t include / \ ? * : [ ]
• Control characters (like \x00 to \x1F) in cell values will confuse Excel’s parser
• Fix: Sanitize sheet names by truncating to 31 chars and replacing forbidden characters with underscores. For cell values, strip or escape any control characters before writing.

4. Writing to an Already Open File #

If your target Excel file is open in Excel (or another program) while your script runs, openpyxl can’t write complete data to it, leading to corruption.

• Fix: Close the file in Excel before running your script, or write to a temporary file first then rename it after saving.

5. Broken Worksheet Structure #

Accidentally deleting the only worksheet in the workbook, or trying to write to a non-existent sheet, can break the file’s internal structure.

• Fix: Double-check that you’re working with a valid worksheet. If you delete the default sheet, create a new one before writing data:

wb = Workbook()
wb.remove(wb.active)  # If you need to delete the default sheet
ws = wb.create_sheet("MongoDB_Data")  # Create a new sheet before writing

6. Outdated Openpyxl Version #

Older versions of openpyxl have known bugs that can cause workbook corruption, especially with newer Excel features.

• Fix: Update to the latest stable version:

pip install --upgrade openpyxl

Bonus Tip: Check Excel’s Detailed Error Message #

When Excel says "We found a problem...", click "Show Details"—it usually tells you exactly what’s wrong (e.g., invalid data in cell A10, corrupted sheet structure) which can save you tons of troubleshooting time.

内容的提问来源于stack exchange，提问作者André