AI prompts for coding

Summary: this function takes a list of email addresses and returns a new list with duplicates removed, ignoring capital letters. It keeps the original order.

def unique_emails(emails):
    seen = set()          # remembers emails we've already kept
    result = []
    for e in emails:
        key = e.strip().lower()   # " A@x.com" and "a@x.com" count as the same
        if key not in seen:
            seen.add(key)
            result.append(e)
    return result

Watch out: it returns the original spelling of the first copy, so “A@X.com” may survive instead of “a@x.com”. If you want clean output, append key instead of e.

Most likely cause (90%)
products is undefined on the first render, because the data hasn’t loaded from the API yet, so products.map() crashes.

Fix

const [products, setProducts] = useState([]);   // start with an empty array
...
{products?.map(p => <Card key={p.id} {...p} />)}

Check it worked: reload the page with the Network tab throttled to “Slow 3G”. The page should show an empty list first, then the products, with no red error.

Other possible causes

2. The API returns { data: [...] }, so you need response.data, not response
3. A typo in the prop name passed from the parent component

Step 1: install Python from python.org (tick “Add Python to PATH” during setup).
Step 2: open Command Prompt and run: pip install pillow
Step 3: save the code below as rename_photos.py in the photos folder.

from pathlib import Path
from PIL import Image

folder = Path(__file__).parent
for photo in folder.glob("*.jpg"):
    date = Image.open(photo).getexif().get(306)   # 306 = "date taken"
    if not date:
        print("No date found, skipping:", photo.name)
        continue
    new_name = date.replace(":", "-").replace(" ", "_") + ".jpg"
    target = folder / new_name
    if target.exists():
        print("Already exists, skipping:", new_name)   # never overwrites
        continue
    photo.rename(target)
    print(photo.name, "→", new_name)

Step 4: double-click the file, or run python rename_photos.py. Test on a copy of the folder first!

const TAX_RATE = 0.18;
const FREE_SHIPPING_ABOVE = 999;

function subtotal(items) {
  return items.reduce((sum, item) => sum + item.price * item.qty, 0);
}

function shippingFee(amount) {
  return amount >= FREE_SHIPPING_ABOVE ? 0 : 49;
}

function orderTotal(items, coupon) {
  const beforeDiscount = subtotal(items);
  const afterDiscount = applyCoupon(beforeDiscount, coupon);
  return afterDiscount * (1 + TAX_RATE) + shippingFee(afterDiscount);
}

What changed

• Split one long function into 4 small ones with clear names
• Replaced magic numbers (0.18, 999) with named constants
• Removed a duplicated loop that calculated the subtotal twice

import pytest
from shop import calculate_discount

def test_applies_10_percent_discount():
    assert calculate_discount(1000, 10) == 900

def test_zero_percent_returns_original_price():
    assert calculate_discount(500, 0) == 500

def test_100_percent_makes_it_free():
    assert calculate_discount(500, 100) == 0

def test_rounds_to_two_decimal_places():
    assert calculate_discount(99.99, 15) == 84.99

def test_negative_percent_raises_error():
    with pytest.raises(ValueError):
        calculate_discount(500, -5)

def test_text_instead_of_number_raises_error():
    with pytest.raises(TypeError):
        calculate_discount("500", 10)

Must-fix

1. SQL injection (line 14). "... WHERE email = '$email'" puts user input straight into the query. Use prepared statements.
2. No CSRF protection. Anyone can submit this form from another site.

Should-fix

3. Email validation only checks for “@”. Use filter_var($email, FILTER_VALIDATE_EMAIL).
4. Errors are shown to the user with die(mysqli_error()), which leaks database details.

Nice-to-have

5. Move the database password to an environment variable.
6. Rename $x and $data2 to say what they hold.

Put this in F2, with the customer name in E2:

=SUMIFS(C:C, B:B, E2, A:A, ">="&EOMONTH(TODAY(),-1)+1, A:A, "<="&EOMONTH(TODAY(),0))

How it works

• SUMIFS adds up column C only where every condition is true
• B:B, E2: the customer matches the name in E2
• EOMONTH(TODAY(),-1)+1 is the 1st of this month
• EOMONTH(TODAY(),0) is the last day of this month

Drag F2 down to fill it for every customer in column E.

Simple stack for a beginner: Next.js + Supabase (database and login) + Vercel (free hosting)

Data to store: classes (time, teacher, capacity) · bookings (user, class, status) · users (name, phone)

Screens: class timetable · class details + “Book” button · my bookings · admin: add/edit classes

Build order (each step works on its own)

1. Static timetable page with fake data
2. Real classes from the database
3. Login with phone number
4. Booking a class (and stopping when it’s full)
5. “My bookings” + cancel
6. Admin page for teachers

Harder than it sounds: handling two people booking the last spot at the same time, and sending WhatsApp reminders (needs a paid API).

import { readFile } from "node:fs/promises";
import { parse } from "csv-parse/sync";

const text = await readFile("orders.csv", "utf8");
const rows = parse(text, { columns: true, skip_empty_lines: true });

const total = rows.reduce((sum, row) => sum + Number(row.amount), 0);
console.log(`Total: ₹${total.toFixed(2)}`);

Install: npm install csv-parse

Behaviour differences

• Python’s csv.DictReader returns text; so does csv-parse, so Number() is needed before adding
• Top-level await needs "type": "module" in package.json