xls2xlsx

xls2xlsx converts Excel 97–2003 .xls workbooks to .xlsx or .xlsm directly from the published file-format specifications.

The distribution is named msxls2xlsx. The Python package and command-line program are both named xls2xlsx.

The converter uses only the Python standard library at runtime. It does not require xlrd, openpyxl, Pillow, olefile, Microsoft Excel, LibreOffice, COM, Java, or external processes.

Installation

python -m pip install msxls2xlsx

To install from source:

python -m pip install .

Python API

Import convert for normal conversions:

from xls2xlsx import convert

result = convert("input.xls", "output.xlsx")

print(result.output_path)
print(result.report.warnings)
print(result.report.statistics)

The converter does not overwrite existing files unless overwrite=True is set. It preserves styles, VBA, and an exact copy of the source workbook by default:

result = convert(
    "input.xls",
    "output.xlsx",
    overwrite=True,
    preserve_styles=True,
    preserve_vba=True,
    preserve_source=True,
)

When no destination is given, a regular workbook is written as .xlsx. A workbook containing VBA is written as .xlsm unless VBA preservation is disabled.

Inspect a workbook without converting it

inspect_xls is optional and independent of conversion. Use it when you need to examine the BIFF version, sheet list, VBA status, or container metadata without creating an output file:

from xls2xlsx import inspect_xls

info = inspect_xls("input.xls")
print(info.to_dict())

Command line

Convert one workbook

xls2xlsx input.xls
xls2xlsx input.xls -o output.xlsx --report report.json

Inspect a workbook

xls2xlsx inspect input.xls
xls2xlsx inspect input.xls --json

The inspect command is read-only and does not create an .xlsx or .xlsm file.

Convert a directory

xls2xlsx batch ./legacy -o ./converted
xls2xlsx batch ./legacy -o ./converted --recursive --report batch.json

Batch conversion:

• ignores Excel ~$ lock files;
• processes files in deterministic relative-path order;
• preserves the input directory structure under the output directory;
• isolates failures so one invalid workbook does not stop the batch;
• checks for output and report-path collisions before conversion;
• exits with status 1 when some files fail.

Recover the original XLS file

xls2xlsx recover converted.xlsx -o recovered.xls

Recovery verifies the embedded file's length and SHA-256 digest. The same operation is available through the Python API:

from xls2xlsx import read_original_source, recover_original_source

stored = read_original_source("converted.xlsx")
recover_original_source("converted.xlsx", "recovered.xls")

Common options

--overwrite          Replace existing output and report files
--no-styles          Skip style conversion
--no-vba             Discard VBA and write an .xlsx file
--no-source-archive  Do not embed the original XLS file
--report FILE        Write a structured JSON report atomically
--json               Print structured output as JSON
--quiet              Suppress success messages

Exit status 0 means success, 1 means conversion failure or partial batch failure, and 2 means invalid input or command usage.

Conversion reports

Reports use a stable top-level structure:

{
  "source": "/path/input.xls",
  "destination": "/path/output.xlsx",
  "diagnostics": [],
  "statistics": {
    "sheets": 1,
    "cells": 42,
    "vba_preserved": false,
    "source_archive_preserved": true
  }
}

Diagnostics have info, warning, or error severity. A diagnostic location may identify a worksheet, cell, OLE stream, or BIFF offset. JSON reports are written to a temporary file in the destination directory and then replaced atomically.

Source preservation and fidelity

The project provides two layers of preservation:

1. Native conversion. BIFF and OfficeArt content that has an OOXML equivalent is converted to editable .xlsx or .xlsm content.
2. Byte-for-byte source preservation. The complete original .xls file is embedded in a custom XML part by default, together with its file name, length, SHA-256 digest, and conversion report.

Recoverable source data does not mean that every runtime behavior can be reproduced in OOXML. ActiveX events, legacy OLE activation, some combined or 3D charts, and complex grouped shapes have no exact OOXML equivalent. The converter reports these cases and keeps the original bytes in the embedded source archive.

Using --no-source-archive or preserve_source=False disables byte-for-byte source recovery.

Supported content

• Text, numbers, booleans, errors, dates, formulas, and cached formula values
• Fonts, colors, fills, borders, alignment, number formats, and protection
• Rich text, merged cells, row and column sizing, hiding, grouping, and outlines
• Sheet order and visibility, active sheets, panes, and page breaks
• Hyperlinks, comments, conditional formatting, data validation, filters, and print settings
• JPEG, PNG, DIB/BMP, TIFF, WMF, and EMF images
• Line, bar, area, pie, and scatter charts, including titles, legends, and series
• Basic DrawingML shapes and the original payloads of embedded OLE objects
• VBA projects and module streams in .xlsm output

Format references

The implementation is based primarily on Microsoft's published MS-CFB, MS-XLS, and MS-ODRAW documentation, together with the published ISO/IEC 29500 implementation notes.

Related projects

xls2xlsx follows the same package and command conventions as doc2docx and ppt2pptx:

Distribution	Python package / CLI	Conversion
msdoc2docx	doc2docx	DOC to DOCX
msxls2xlsx	xls2xlsx	XLS to XLSX/XLSM
ppt2pptx	ppt2pptx	PPT to PPTX

The projects share a consistent API, CLI structure, report format, and exit status conventions. Their conversion engines remain separate because the Word, Excel, and PowerPoint binary formats use different data models.

Development

Run the test suite with:

PYTHONPATH=src python -m unittest discover -s tests -v

The tests cover protocol parsing, formulas, styles, objects, VBA, source recovery, structured reports, CLI workflows, isolated installation, and real .xls fixtures from Apache POI. Fixture licensing information is available in tests/fixtures/apache-poi/.

License

This project is licensed under the MIT License.