A Python script that splits a large Excel or CSV file into smaller ones by row count or by a column

Example result

python merge_sales.py --month 2026-10

2026-11-02 09:14:03 INFO  Folder: sales/2026-10, 9 files found
2026-11-02 09:14:03 INFO  shop-01.csv: 1,284 rows
2026-11-02 09:14:04 INFO  shop-02.xlsx: 967 rows
2026-11-02 09:14:04 WARN  shop-07.csv: 3 rows without a price skipped (lines 88, 412, 913)
2026-11-02 09:14:05 INFO  Done: 10,412 rows -> report-2026-10.xlsx (sheets "Sales" and "Totals")

[columns]
date = Date, Sale date, Day
product = Product, Item, Name
quantity = Qty, Quantity, Pcs
price = Price, Unit price

def read_shop_file(path: Path, columns: dict[str, list[str]]) -> pd.DataFrame:
    """Reads one shop's file and gives it the report's column names."""
    table = pd.read_excel(path) if path.suffix == ".xlsx" else pd.read_csv(path, encoding="utf-8-sig")
    renamed = {}
    for name, variants in columns.items():
        found = next((c for c in table.columns if c.strip() in variants), None)
        if found is None:
            raise ReportError(f"{path.name}: no column for '{name}' (looked for {', '.join(variants)})")
        renamed[found] = name
    table = table.rename(columns=renamed)[list(columns)]
    table["shop"] = path.stem
    return table

About this service

A table with hundreds of thousands of rows is hard to open, too big for an import form that takes 5,000 rows at a time, or has to be sent in parts to different people. This Python script splits it for you: into parts of a set number of rows, or by the value in a column, so each region, store or sales rep gets their own file. Each part keeps the header row and the column order, and the files are named the way you want, such as orders_north.xlsx. It reads CSV and Excel and saves either. Send us a few rows of the table and the rule. You run the script yourself on your computer, and the original file is never changed. It splits data; it does not check or fix the values in it.

What is included

• What you getA ZIP archive with the Python script, a README with step-by-step instructions and, from Standard, a settings file with the split rule and file names; the code is also shown on the order page.
• By rows or by columnEqual parts, or one file for each value
• Header in every partEach file opens and imports on its own
• Your file namesWith a number or the column value in the name
• Original untouchedParts are saved to a separate folder
• Readable codeWith comments, easy to change the rule later

How it works

1. 1
   TaskYou send a few rows and say how to split the file
2. 2
   CodeWe write the script and the guide to running it
3. 3
   Try itYou run it on your file and check the parts
4. 4
   ChangesYou ask for changes within your package and send any error message

What we need from you

The first 10-20 rows of the table as CSV or Excel (real names and numbers can be replaced), how many rows the full file has and how big it is, and the rule: so many rows per part, or one file per value of a column (name the column). How the parts should be named, CSV or Excel, and whether they go to separate files or sheets of one workbook. Your system: Windows, macOS or Linux.

We will ask you:

• Which file do you need to split?
• How should it be split?
• What should the parts be?
• Where will it run?

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Questions and answers

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