Python XLSB Reader & Writer

A Python library for reading and writing XLSB and XLSX files efficiently.

Installation

pip install xlspy

Usage

Basic Example

from xlspy import XlsbWriter
import datetime
from decimal import Decimal

data = [
    ["Name", "Age", "City", "info"],
    [-123, 2147483647, 2147483648, 2147483999],
    ["x", "y", "z", datetime.datetime.today()],
    ["Alice", 25, "New York", datetime.date.today()],
    ["Bob", 30, "London", Decimal(3.14)],
    ["Charlie", 35, "Paris", datetime.datetime.now()],
    [True, False, None, datetime.datetime.utcnow()]
]

# Initialize writer with a specific compression level
with XlsbWriter("output.xlsb", compressionLevel=6) as writer:
    # Add a visible sheet
    writer.add_sheet("Visible Sheet")
    writer.write_sheet(data)

    # Add a hidden sheet
    writer.add_sheet("Hidden Sheet", hidden=True)
    writer.write_sheet([["This sheet is hidden."]])

XlsxWriter Example

from xlspy import XlsxWriter
import datetime
from decimal import Decimal

data = [
    ["Name", "Age", "City", "info"],
    [-123, 2147483647, 2147483648, 2147483999],
    ["x", "y", "z", datetime.datetime.today()],
    ["Alice", 25, "New York", datetime.date.today()],
    ["Bob", 30, "London", Decimal(3.14)],
    ["Charlie", 35, "Paris", datetime.datetime.now()],
    [True, False, None, datetime.datetime.utcnow()]
]

# Initialize writer with a specific compression level
with XlsxWriter("output.xlsx", compressionLevel=6) as writer:
    # Add a visible sheet
    writer.add_sheet("Visible Sheet")
    writer.write_sheet(data)

    # Add a hidden sheet
    writer.add_sheet("Hidden Sheet", hidden=True)
    writer.write_sheet([["This sheet is hidden."]])

Cell Formatting (Number, Date, DateTime)

xlspy supports custom cell formatting for numbers, dates, and datetimes in both XLSB and XLSX output. Pass a (value, format_string) tuple to apply a format to a specific cell.

from xlspy import XlsxWriter, F  # or XlsbWriter
import datetime

with XlsxWriter("formatted.xlsx") as writer:
    writer.add_sheet("Formats")
    writer.write_sheet([
        ["Description", "Value"],
        ["Thousands separator", (100000, F.THOUSANDS_SEP)],
        ["Currency PLN",       (100000, F.CURRENCY_PLN)],
        ["Currency EUR",       (100000, F.CURRENCY_EUR)],
        ["Percentage",         (100000, F.PERCENTAGE)],
        ["Scientific",         (100000, F.SCIENTIFIC)],
        ["Two decimals",       (100000, F.TWO_DECIMALS)],
        ["Text",               (100000, F.TEXT)],
        ["Leading zeros",      (100000, F.LEADING_ZEROS)],
        ["Short date",         (datetime.date(2026,6,1), F.DATE_SHORT)],
        ["Long date",          (datetime.date(2026,6,1), F.DATE_LONG)],
        ["ISO date",           (datetime.date(2026,6,1), F.DATE_ISO)],
        ["Month + year",       (datetime.date(2026,6,1), F.DATE_MONTH_YEAR)],
        ["Weekday + date",     (datetime.date(2026,6,1), F.DATE_WEEKDAY)],
        ["Short datetime",     (datetime.datetime(2026,6,1,14,34), F.DATETIME_SHORT)],
        ["Time only",          (datetime.datetime(2026,6,1,14,34), F.TIME_HH_MM)],
        ["12h time",           (datetime.datetime(2026,6,1,14,34), F.TIME_12H)],
        ["ISO datetime",       (datetime.datetime(2026,6,1,14,34), F.DATETIME_ISO)],
    ])

Available Format Constants (xlspy.F)

Number	Date	DateTime
F.THOUSANDS_SEP — #,##0	F.DATE_SHORT — dd.mm.yyyy	F.DATETIME_SHORT — dd.mm.yyyy hh:mm
F.CURRENCY_PLN — #,##0.00 "zł"	F.DATE_LONG — d mmmm yyyy	F.DATETIME_LONG — d mmmm yyyy hh:mm:ss
F.CURRENCY_EUR — #,##0.00 €	F.DATE_DAY_MONTH_YEAR — dd-mm-yyyy	F.TIME_HH_MM — hh:mm
F.PERCENTAGE — 0%	F.DATE_ISO — yyyy-mm-dd	F.TIME_HH_MM_SS — hh:mm:ss
F.SCIENTIFIC — 0.00E+00	F.DATE_MONTH_YEAR — mmmm yyyy	F.TIME_12H — h:mm AM/PM
F.TWO_DECIMALS — #,##0.00	F.DATE_WEEKDAY — dddd, d mmmm yyyy	F.DATETIME_24H — dd.mm.yyyy hh:mm:ss
F.TEXT — @	F.DATE_DAY_MONTH — d mmmm	F.DATETIME_ISO — yyyy-mm-dd"T"hh:mm:ss
F.LEADING_ZEROS — 000000000	F.DATE_YEAR_ONLY — yyyy	F.TIME_MS — hh:mm:ss.000

You can also use custom format strings directly:

writer.write_sheet([
    ["Custom", (1234.56, '#,##0.00 "USD"')],
    ["Date",   (datetime.date(2026,6,1), 'dd.mm.yyyy')],
])

The formatting works transparently on both XlsxWriter and XlsbWriter.

Reading XLSB and XLSX Files

Reading files is done via the ExcelReader class, which automatically detects the format.

from xlspy import ExcelReader

with ExcelReader("input.xlsx") as reader:  # or .xlsb
    names = reader.get_sheet_names()
    print(f"Sheets: {names}")

    for sheet_name in names:
        rows = reader.read_all(sheet_name)
        for row in rows:
            print(row)

# Generator usage (memory efficient for large files):
with ExcelReader("large_file.xlsb") as reader:
    for row in reader.get_rows("Sheet1"):
        print(row)

Streaming from a Database (Netezza)

This example shows how to stream data directly from a database query into an XLSB file using nzpy-extended. This is highly memory-efficient as it doesn't load the entire dataset into memory.

First, ensure you have nzpy-extended installed:

pip install nzpy-extended

Then, you can use a generator function to feed data to XlsbWriter.

import os
from typing import Generator
from xlspy import XlsbWriter

# --- Configuration ---
NZ_CONFIG = {
    "host": os.environ.get("NZ_DEV_HOST", "your_host"),
    "port": int(os.environ.get("NZ_DEV_PORT", "5480")),
    "database": os.environ.get("NZ_DEV_DB", "your_db"),
    "user": os.environ.get("NZ_DEV_USER", "your_user"),
    "password": os.environ.get("NZ_DEV_PASSWORD", "your_password"),
}
QUERY = "SELECT * FROM YourTable"
OUTPUT_FILENAME = "db_output.xlsb"


def row_generator(cursor) -> Generator[list, None, None]:
    """Yields column headers first, then each data row."""
    headers = [column[0] for column in cursor.description]
    yield headers
    while row := cursor.fetchone():
        yield list(row)


# --- Main Execution ---
try:
    import nzpy_extended.sync as nzpy

    with nzpy.connect(**NZ_CONFIG) as conn:
        cursor = conn.cursor()
        cursor.execute(QUERY)

        with XlsbWriter(OUTPUT_FILENAME) as writer:
            writer.add_sheet("Database Export")
            writer.write_sheet(row_generator(cursor))
            writer.add_sheet("SQL Query", hidden=True)
            writer.write_sheet([["SQL"], [QUERY]])

    print(f"Successfully created '{OUTPUT_FILENAME}'")

except Exception as e:
    print(f"An unexpected error occurred: {e}")

Performance

xlspy is designed for high performance. Since version 0.1.0, the library includes a C extension (_c_core) that accelerates XLSB read and write. The C extension is enabled by default (compiled automatically on install). Set XLSPY_DISABLE_C_EXT=1 to force the pure Python fallback.

All benchmarks: 50000 × 50 dataset (2.5M cells). Tests performed on Windows 11 (Python 3.14, AMD64).

Write

Library	Format	Time	Size
xlspy (C_EXT)	XLSB	1.02 s	7.25 MB
xlspy (Python)	XLSB	2.54 s	7.25 MB
xlspy	XLSX	5.35 s	6.34 MB
xlsxwriter	XLSX	9.80 s	11.57 MB

Read

Library	Format	Time	Notes
xlspy (C_EXT)	XLSB	1.39 s	default, compiled C
xlspy	XLSX	4.72 s	uses expat XML parser (C)
xlspy (Python)	XLSB	6.41 s	pure Python fallback
openpyxl	XLSX	7.85 s	read-only mode

Analysis

The 4.6× read speedup comes from two factors:

• ~60–70% — native C compilation, no interpreter overhead per record
• ~30–40% — algorithm simplification: flat array indexed by col − first_col instead of Dict[int, Any], no isinstance per cell, no BiffReader.read_worksheet() method call per record

Run the benchmarks yourself with examples/performance_test.py.

Repository

https://github.com/KrzysztofDusko/xlspy/