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feat: update the saving lesson of the JS2 course to be about JavaScript #1762

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4d2824c
style: change order, first json, then csv
honzajavorek Jun 27, 2025
0831842
fix: various improvements to the Python lesson about saving data
honzajavorek Jun 27, 2025
03d2408
fix: update saving to be about JS
honzajavorek Jun 27, 2025
3b3a626
fix: missing semicolon in saving data
honzajavorek Jun 30, 2025
38f6fc2
fix: make it clearer in saving data that we append more code
honzajavorek Jun 30, 2025
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293 changes: 142 additions & 151 deletions sources/academy/webscraping/scraping_basics_javascript2/08_saving_data.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,9 @@ unlisted: true
We managed to scrape data about products and print it, with each product separated by a new line and each field separated by the `|` character. This already produces structured text that can be parsed, i.e., read programmatically.

```text
$ python main.py
JBL Flip 4 Waterproof Portable Bluetooth Speaker | 74.95 | 74.95
Sony XBR-950G BRAVIA 4K HDR Ultra HD TV | 1398.00 | None
$ node index.js
JBL Flip 4 Waterproof Portable Bluetooth Speaker | 7495 | 7495
Sony XBR-950G BRAVIA 4K HDR Ultra HD TV | 139800 | null
...
```

Expand All @@ -27,220 +27,211 @@ We should use widely popular formats that have well-defined solutions for all th

Producing results line by line is an efficient approach to handling large datasets, but to simplify this lesson, we'll store all our data in one variable. This'll take three changes to our program:

```py
import httpx
from bs4 import BeautifulSoup
from decimal import Decimal

url = "https://warehouse-theme-metal.myshopify.com/collections/sales"
response = httpx.get(url)
response.raise_for_status()

html_code = response.text
soup = BeautifulSoup(html_code, "html.parser")

# highlight-next-line
data = []
for product in soup.select(".product-item"):
title = product.select_one(".product-item__title").text.strip()

price_text = (
product
.select_one(".price")
.contents[-1]
.strip()
.replace("$", "")
.replace(",", "")
)
if price_text.startswith("From "):
min_price = Decimal(price_text.removeprefix("From "))
price = None
else:
min_price = Decimal(price_text)
price = min_price

# highlight-next-line
data.append({"title": title, "min_price": min_price, "price": price})

# highlight-next-line
print(data)
```js
import * as cheerio from 'cheerio';

const url = "https://warehouse-theme-metal.myshopify.com/collections/sales";
const response = await fetch(url);

if (response.ok) {
const html = await response.text();
const $ = cheerio.load(html);

// highlight-next-line
const data = [];
$(".product-item").each((i, element) => {
const productItem = $(element);

const title = productItem.find(".product-item__title");
const titleText = title.text().trim();

const price = productItem.find(".price").contents().last();
const priceRange = { minPrice: null, price: null };
const priceText = price
.text()
.trim()
.replace("$", "")
.replace(".", "")
.replace(",", "");

if (priceText.startsWith("From ")) {
priceRange.minPrice = parseInt(priceText.replace("From ", ""));
} else {
priceRange.minPrice = parseInt(priceText);
priceRange.price = priceRange.minPrice;
}

// highlight-next-line
data.push({ title: titleText, ...priceRange });
});

// highlight-next-line
console.log(data);
} else {
throw new Error(`HTTP ${response.status}`);
}
```

Before looping over the products, we prepare an empty list. Then, instead of printing each line, we append the data of each product to the list in the form of a Python dictionary. At the end of the program, we print the entire list at once.
Before looping over the products, we prepare an empty array. Then, instead of printing each line, we append the data of each product to the array in the form of a JavaScript object. At the end of the program, we print the entire array at once.

```text
$ python main.py
[{'title': 'JBL Flip 4 Waterproof Portable Bluetooth Speaker', 'min_price': Decimal('74.95'), 'price': Decimal('74.95')}, {'title': 'Sony XBR-950G BRAVIA 4K HDR Ultra HD TV', 'min_price': Decimal('1398.00'), 'price': None}, ...]
$ node index.js
[
{
title: 'JBL Flip 4 Waterproof Portable Bluetooth Speaker',
minPrice: 7495,
price: 7495
},
{
title: 'Sony XBR-950G BRAVIA 4K HDR Ultra HD TV',
minPrice: 139800,
price: null
},
...
]
```

:::tip Pretty print
:::tip Spread syntax

The three dots in `{ title: titleText, ...priceRange }` are called [spread syntax](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax). It's the same as if we wrote the following:

If you find the complex data structures printed by `print()` difficult to read, try using [`pp()`](https://docs.python.org/3/library/pprint.html#pprint.pp) from the `pprint` module instead.
```js
{
title: titleText,
minPrice: priceRange.minPrice,
price: priceRange.price,
}
```

:::

## Saving data as CSV
## Saving data as JSON

The CSV format is popular among data analysts because a wide range of tools can import it, including spreadsheets apps like LibreOffice Calc, Microsoft Excel, Apple Numbers, and Google Sheets.
The JSON format is popular primarily among developers. We use it for storing data, configuration files, or as a way to transfer data between programs (e.g., APIs). Its origin stems from the syntax of JavaScript objects, but people now use it accross programming languages.

In Python, it's convenient to read and write CSV files, thanks to the [`csv`](https://docs.python.org/3/library/csv.html) standard library module. First let's try something small in the Python's interactive REPL to familiarize ourselves with the basic usage:
We'll begin with importing the `writeFile` function from the Node.js standard library, so that we can, well, write files:

```py
>>> import csv
>>> with open("data.csv", "w") as file:
... writer = csv.DictWriter(file, fieldnames=["name", "age", "hobbies"])
... writer.writeheader()
... writer.writerow({"name": "Alice", "age": 24, "hobbies": "kickbox, Python"})
... writer.writerow({"name": "Bob", "age": 42, "hobbies": "reading, TypeScript"})
...
```js
import * as cheerio from 'cheerio';
// highlight-next-line
import { writeFile } from "fs/promises";
```

We first opened a new file for writing and created a `DictWriter()` instance with the expected field names. We instructed it to write the header row first and then added two more rows containing actual data. The code produced a `data.csv` file in the same directory where we're running the REPL. It has the following contents:
Next, instead of printing the data, we'll finish the program by exporting it to JSON. Let's replace the line `console.log(data)` with the following:

```csv title=data.csv
name,age,hobbies
Alice,24,"kickbox, Python"
Bob,42,"reading, TypeScript"
```js
const jsonData = JSON.stringify(data);
await writeFile('products.json', jsonData);
```

In the CSV format, if values contain commas, we should enclose them in quotes. You can see that the writer automatically handled this.

When browsing the directory on macOS, we can see a nice preview of the file's contents, which proves that the file is correct and that other programs can read it as well. If you're using a different operating system, try opening the file with any spreadsheet program you have.

![CSV example preview](images/csv-example.png)

Now that's nice, but we didn't want Alice, Bob, kickbox, or TypeScript. What we actually want is a CSV containing `Sony XBR-950G BRAVIA 4K HDR Ultra HD TV`, right? Let's do this! First, let's add `csv` to our imports:
That's it! If we run our scraper now, it won't display any output, but it will create a `products.json` file in the current working directory, which contains all the data about the listed products:

```py
import httpx
from bs4 import BeautifulSoup
from decimal import Decimal
# highlight-next-line
import csv
<!-- eslint-skip -->
```json title=products.json
[{"title":"JBL Flip 4 Waterproof Portable Bluetooth Speaker","minPrice":7495,"price":7495},{"title":"Sony XBR-950G BRAVIA 4K HDR Ultra HD TV","minPrice":139800,"price":null},...]
```

Next, instead of printing the data, we'll finish the program by exporting it to CSV. Replace `print(data)` with the following:
If you skim through the data, you'll notice that the `JSON.stringify()` function handled some potential issues, such as escaping double quotes found in one of the titles by adding a backslash:

```py
with open("products.csv", "w") as file:
writer = csv.DictWriter(file, fieldnames=["title", "min_price", "price"])
writer.writeheader()
for row in data:
writer.writerow(row)
```json
{"title":"Sony SACS9 10\" Active Subwoofer","minPrice":15800,"price":15800}
```

If we run our scraper now, it won't display any output, but it will create a `products.csv` file in the current working directory, which contains all the data about the listed products.
:::tip Pretty JSON

![CSV preview](images/csv.png)
While a compact JSON file without any whitespace is efficient for computers, it can be difficult for humans to read. You can call `JSON.stringify(data, null, 2)` for prettier output. See [documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify) for explanation of the parameters and more examples.

## Saving data as JSON
:::

The JSON format is popular primarily among developers. We use it for storing data, configuration files, or as a way to transfer data between programs (e.g., APIs). Its origin stems from the syntax of objects in the JavaScript programming language, which is similar to the syntax of Python dictionaries.
## Saving data as CSV

In Python, there's a [`json`](https://docs.python.org/3/library/json.html) standard library module, which is so straightforward that we can start using it in our code right away. We'll need to begin with imports:
The CSV format is popular among data analysts because a wide range of tools can import it, including spreadsheets apps like LibreOffice Calc, Microsoft Excel, Apple Numbers, and Google Sheets.

```py
import httpx
from bs4 import BeautifulSoup
from decimal import Decimal
import csv
# highlight-next-line
import json
```
Neither JavaScript itself nor Node.js offers anything built-in to read and write CSV, so we'll need to install a library. We'll use [json2csv](https://juanjodiaz.github.io/json2csv/), a _de facto_ standard for working with CSV in JavaScript:

Next, let’s append one more export to end of the source code of our scraper:
```text
$ npm install @json2csv/node --save

```py
with open("products.json", "w") as file:
json.dump(data, file)
added 4 packages, and audited 28 packages in 1s
...
```

That’s it! If we run the program now, it should also create a `products.json` file in the current working directory:
Once installed, we can add the following line to our imports:

```text
$ python main.py
Traceback (most recent call last):
...
raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type Decimal is not JSON serializable
```js
import * as cheerio from 'cheerio';
import { writeFile } from "fs/promises";
// highlight-next-line
import { AsyncParser } from '@json2csv/node';
```

Ouch! JSON supports integers and floating-point numbers, but there's no guidance on how to handle `Decimal`. To maintain precision, it's common to store monetary values as strings in JSON files. But this is a convention, not a standard, so we need to handle it manually. We'll pass a custom function to `json.dump()` to serialize objects that it can't handle directly:
Then, let's add one more data export near the end of the source code of our scraper:

```py
def serialize(obj):
if isinstance(obj, Decimal):
return str(obj)
raise TypeError("Object not JSON serializable")
```js
const jsonData = JSON.stringify(data);
await writeFile('products.json', jsonData);

with open("products.json", "w") as file:
json.dump(data, file, default=serialize)
const parser = new AsyncParser();
const csvData = await parser.parse(data).promise();
await writeFile("products.csv", csvData);
```

Now the program should work as expected, producing a JSON file with the following content:
The program should now also produce a `data.csv` file. When browsing the directory on macOS, we can see a nice preview of the file's contents, which proves that the file is correct and that other programs can read it. If you're using a different operating system, try opening the file with any spreadsheet program you have.

<!-- eslint-skip -->
```json title=products.json
[{"title": "JBL Flip 4 Waterproof Portable Bluetooth Speaker", "min_price": "74.95", "price": "74.95"}, {"title": "Sony XBR-950G BRAVIA 4K HDR Ultra HD TV", "min_price": "1398.00", "price": null}, ...]
```
![CSV preview](images/csv.png)

If you skim through the data, you'll notice that the `json.dump()` function handled some potential issues, such as escaping double quotes found in one of the titles by adding a backslash:
In the CSV format, if a value contains commas, we should enclose it in quotes. If it contains quotes, we should double them. When we open the file in a text editor of our choice, we can see that the library automatically handled this:

```json
{"title": "Sony SACS9 10\" Active Subwoofer", "min_price": "158.00", "price": "158.00"}
```csv title=data.csv
"title","minPrice","price"
"JBL Flip 4 Waterproof Portable Bluetooth Speaker",7495,7495
"Sony XBR-950G BRAVIA 4K HDR Ultra HD TV",139800,
"Sony SACS9 10"" Active Subwoofer",15800,15800
...
"Samsung Surround Sound Bar Home Speaker, Set of 7 (HW-NW700/ZA)",64799,64799
...
```

:::tip Pretty JSON

While a compact JSON file without any whitespace is efficient for computers, it can be difficult for humans to read. You can pass `indent=2` to `json.dump()` for prettier output.

Also, if your data contains non-English characters, set `ensure_ascii=False`. By default, Python encodes everything except [ASCII](https://en.wikipedia.org/wiki/ASCII), which means it would save [Bún bò Nam Bô](https://vi.wikipedia.org/wiki/B%C3%BAn_b%C3%B2_Nam_B%E1%BB%99) as `B\\u00fan b\\u00f2 Nam B\\u00f4`.

:::

We've built a Python application that downloads a product listing, parses the data, and saves it in a structured format for further use. But the data still has gaps: for some products, we only have the min price, not the actual prices. In the next lesson, we'll attempt to scrape more details from all the product pages.
We've built a Node.js application that downloads a product listing, parses the data, and saves it in a structured format for further use. But the data still has gaps: for some products, we only have the min price, not the actual prices. In the next lesson, we'll attempt to scrape more details from all the product pages.

---

## Exercises

In this lesson, you learned how to create export files in two formats. The following challenges are designed to help you empathize with the people who'd be working with them.
In this lesson, we created export files in two formats. The following challenges are designed to help you empathize with the people who'd be working with them.

### Process your CSV
### Process your JSON

Open the `products.csv` file in a spreadsheet app. Use the app to find all products with a min price greater than $500.
Write a new Node.js program that reads `products.json`, finds all products with a min price greater than $500, and prints each of them.

<details>
<summary>Solution</summary>

Let's use [Google Sheets](https://www.google.com/sheets/about/), which is free to use. After logging in with a Google account:

1. Go to **File > Import**, choose **Upload**, and select the file. Import the data using the default settings. You should see a table with all the data.
2. Select the header row. Go to **Data > Create filter**.
3. Use the filter icon that appears next to `min_price`. Choose **Filter by condition**, select **Greater than**, and enter **500** in the text field. Confirm the dialog. You should see only the filtered data.
```js
import { readFile } from "fs/promises";

![CSV in Google Sheets](images/csv-sheets.png)
const jsonData = await readFile("products.json");
const data = JSON.parse(jsonData);
data
.filter(row => row.minPrice > 50000)
.forEach(row => console.log(row));
```

</details>

### Process your JSON
### Process your CSV

Write a new Python program that reads `products.json`, finds all products with a min price greater than $500, and prints each one using [`pp()`](https://docs.python.org/3/library/pprint.html#pprint.pp).
Open the `products.csv` file we created in the lesson using a spreadsheet application. Then, in the app, find all products with a min price greater than $500.

<details>
<summary>Solution</summary>

```py
import json
from pprint import pp
from decimal import Decimal
Let's use [Google Sheets](https://www.google.com/sheets/about/), which is free to use. After logging in with a Google account:

with open("products.json", "r") as file:
products = json.load(file)
1. Go to **File > Import**, choose **Upload**, and select the file. Import the data using the default settings. You should see a table with all the data.
2. Select the header row. Go to **Data > Create filter**.
3. Use the filter icon that appears next to `minPrice`. Choose **Filter by condition**, select **Greater than**, and enter **500** in the text field. Confirm the dialog. You should see only the filtered data.

for product in products:
if Decimal(product["min_price"]) > 500:
pp(product)
```
![CSV in Google Sheets](images/csv-sheets.png)

</details>
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