Python automation for boring work: practical guide

Choose the smallest useful approach

Aggregate a three-row CSV without changing the source file

Illustrative example with fictional data. These are not customer results or a promise of time savings or income.

Input

category,amount
books,1200
software,600
books,800

Steps

1. Create an empty working folder and save the input as weekly.csv in UTF-8. Amounts must be non-negative integers in the same unit.
2. Save the code below as summarize.py in that folder. It uses Python 3 and its standard library; no package installation is needed.
3. From a terminal in that folder, run python summarize.py (or python3 summarize.py where that is the installed command).
4. Compare the new totals.csv and console total with the expected result. Use another empty folder for a repeat run: an existing totals.csv causes the script to stop rather than overwrite it.

Runnable example

import csv
from collections import defaultdict
from pathlib import Path

totals = defaultdict(int)
with Path("weekly.csv").open(encoding="utf-8-sig", newline="") as source:
    reader = csv.DictReader(source)
    if len(reader.fieldnames or []) != 2 or set(reader.fieldnames) != {"category", "amount"}:
        raise ValueError("Expected category and amount columns")
    for line, row in enumerate(reader, start=2):
        if None in row or any(value is None for value in row.values()):
            raise ValueError(f"Wrong column count on line {line}")
        category = row["category"].strip()
        raw_amount = row["amount"].strip()
        if not category or category[0] in "=+-@" or not raw_amount.isascii() or not raw_amount.isdigit():
            raise ValueError(f"Invalid category or non-negative integer amount on line {line}")
        totals[category] += int(raw_amount)

# Exclusive creation: an existing result is never overwritten.
with Path("totals.csv").open("x", encoding="utf-8", newline="") as target:
    writer = csv.writer(target)
    writer.writerow(["category", "amount"])
    writer.writerows(sorted(totals.items()))
print(f"{sum(totals.values())} total; {len(totals)} categories")

Expected output

category,amount
books,2000
software,600

Console: 2600 total; 2 categories

The books rows add up to 2,000 and software adds up to 600, giving 2,600 in total. Three input rows become two categories. Extra or missing columns, negative numbers, and decimals are rejected; they are never silently changed to zero.

Before using it on real work

• Work on a copy and confirm that weekly.csv has not changed
• Check both column names, encoding, and a consistent unit for every amount
• Reconcile the input total of 2,600 with the output total of 2,600
• Compare total setup, runtime, review, and repair time against the manual task

When to stop

Stop if columns or units keep changing, you cannot explain the totals, or you have to ignore errors to finish. Standardize the input before expanding the automation.

Next decision

Try three copies of the same format and record the results and effort. Stay with the standard library while it meets the need. Compare a paid tool only after identifying a specific missing transformation, its maintenance cost, and the total price.

No paid product is required for this example. This page does not link to a product offer.