xlsx-fixer 1.0.0

Fix Mac Excel corruption in openpyxl-generated .xlsx files

xlsx-fixer

Fix the Mac Excel "We found a problem with some content" error in openpyxl-generated .xlsx files.

openpyxl hardcodes inline strings (t="inlineStr") for every text cell. Mac Excel's strict OOXML parser rejects this, showing a recovery dialog on every open. Windows Excel silently accepts it, which is why the bug goes unnoticed during development.

xlsx-fixer rewrites the ZIP to use a proper shared string table (xl/sharedStrings.xml), removes inconsistent calc state, and strips illegal control characters. One function call. Zero dependencies beyond the standard library.

The Problem

If you generate .xlsx files with Python's openpyxl library and open them on Mac, you see:

"We found a problem with some content in 'file.xlsx'. Do you want us to try to recover as much as we can?"

After clicking "Yes":

"Removed Records: String properties from /xl/sharedStrings.xml part"

This happens because openpyxl writes every text cell as an inline string (<c t="inlineStr"><is><t>text</t></is></c>) instead of referencing a shared string table. The openpyxl maintainer has declined to fix this for 17+ years.

Install

pip install xlsx-fixer

Zero dependencies. Uses only Python standard library (zipfile, xml.etree.ElementTree).

Usage

Python API

from xlsx_fixer import fix, check

# Fix in-place (after openpyxl wb.save())
from openpyxl import Workbook
wb = Workbook()
ws = wb.active
ws["A1"] = "Hello, Mac Excel!"
wb.save("report.xlsx")

fix("report.xlsx")  # That's it. Mac-safe now.

# Fix to a new file
fix("report.xlsx", output="report_fixed.xlsx")

# Check without modifying
issues = check("report.xlsx")
for issue in issues:
    print(f"[{issue.severity}] {issue.code}: {issue.message}")

CLI

# Fix in-place
xlsx-fixer fix report.xlsx

# Fix to new file
xlsx-fixer fix report.xlsx -o fixed.xlsx

# Check without modifying
xlsx-fixer check report.xlsx

# Version
xlsx-fixer --version

Integration with openpyxl

Add two lines to your existing code:

from openpyxl import Workbook
from xlsx_fixer import fix

wb = Workbook()
# ... your existing workbook code ...

wb.calculation.fullCalcOnLoad = None  # Remove inconsistent calc state
wb.save("output.xlsx")
fix("output.xlsx")  # Convert inline strings to shared string table

What It Fixes

#	Issue	Root Cause	Impact
1	Inline strings	openpyxl hardcodes t="inlineStr" in cell/_writer.py	"We found a problem" dialog on every Mac open
2	fullCalcOnLoad	openpyxl sets fullCalcOnLoad="1" without generating calcChain.xml	Recovery dialog; formulas show 0
3	Stale calcChain.xml	References cells that no longer contain formulas	"Removed Records: Formula" in repair log
4	Control characters	Illegal XML 1.0 chars (U+0000-U+0008, etc.) in cell values	ST_Xstring validation failures

How It Works

1. Reads the entire .xlsx ZIP into memory
2. Parses every xl/worksheets/sheet*.xml
3. Finds all <c t="inlineStr"><is><t>TEXT</t></is></c> cells
4. Builds a deduplicated shared string table
5. Rewrites each cell as <c t="s"><v>INDEX</v></c>
6. Creates xl/sharedStrings.xml with <sst> root element
7. Adds relationship to xl/_rels/workbook.xml.rels
8. Adds Override to [Content_Types].xml
9. Removes fullCalcOnLoad from <calcPr> in xl/workbook.xml
10. Optionally removes stale calcChain.xml
11. Writes new ZIP back to the same (or specified output) path

The fix is idempotent — running it twice is safe and the second run is a no-op.

Performance

The fix operates entirely in-memory. On a real production workbook (11 sheets, 195 properties, 448 verification checks, ~100KB):

• ~30ms on Apple Silicon
• ~50ms on Intel Mac
• Scales linearly with file size

Why Not Just Fix openpyxl?

The maintainer has permanently refused to add shared string table support to the writer. The inline string behavior is hardcoded in cell/_writer.py lines 21-22 and 70-79 with no API flag to change it. This isn't a bug they plan to fix — it's a design decision from 2007.

With 249M+ openpyxl downloads per month and 7,400+ dependent packages, this affects an enormous number of Python developers who generate Excel files for Mac users.

Tested On

• Python 3.9 - 3.14
• openpyxl 3.0.x - 3.1.x
• Mac Excel 16.x (Microsoft 365)
• Windows Excel (passes through unchanged)
• LibreOffice Calc (passes through unchanged)

License

MIT License. See LICENSE for details.