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🌐 CSS Scraper Provider (css_scraper)

The CSS Scraper is a versatile provider that can extract a price from any public webpage using a CSS selector. It is one of the Asset Providers — it does not rely on a specific financial data API.

📖 User Guide: CSS Scraper — User Manual

⚙️ How it Works

  1. Configuration: When assigning this provider to an asset, you must provide:

    • identifier: The URL of the webpage to scrape.
    • identifier_type: URL — the form's input type; it is stored as IdentifierType.OTHER (map_input_type_to_identifier_type), which is why test_cases use OTHER.
    • provider_params:
      • current_css_selector (required): The CSS selector to locate the price element on the page (e.g., #sp-last, .price-value).
      • currency (required): The currency of the price (ISO 4217).
      • decimal_format (optional): us (e.g., 1,234.56) or eu (e.g., 1.234,56). Default: us.
      • timeout (optional): HTTP request timeout in seconds. Default: 30.
      • user_agent (optional): Custom User-Agent header. Default: LibreFolio/1.0.
      • headers (optional, not in params_schema, so not in the form): a dict of extra HTTP headers merged over the defaults (User-Agent, Accept, Accept-Language: en-US,en;q=0.5) with mergedeep.

  2. Execution:

    • Fetches the HTML of the specified URL via httpx — a fresh httpx.AsyncClient(timeout=…) per call, follow_redirects=True, then raise_for_status().
    • Uses BeautifulSoup (html.parser) and select_one() — the first element matching the selector. No JavaScript runs, so a price rendered client-side is invisible to the scraper.
    • Extracts the text content and parses it into a Decimal value, handling different number formats based on decimal_format.
    • as_of_date is always today. During a refresh the core stores that value as the day's price point, so a history builds up one sync at a time.

  3. get_asset_url(): Returns the identifier URL itself (the page being scraped).

  4. params_schema: Exposes all 5 configuration fields for dynamic form generation in the frontend. The fields declare no label, so the form shows the raw keys as captions, with each description as tooltip.

Error codes raised by get_current_value() (history always raises NOT_IMPLEMENTED):

Code When Message starts with
MISSING_PARAMS No params, or current_css_selector / currency missing CSS scraper requires provider_params / Missing required params
INVALID_PARAMS decimal_format other than us / eu decimal_format must be 'us' or 'eu'
NOT_FOUND The selector matches nothing Price element not found with selector
PARSE_ERROR Empty or non-numeric text Empty price text / Failed to parse price
HTTP_ERROR Non-2xx response HTTP error {status}: {reason}
REQUEST_ERROR Network error or timeout (httpx.RequestError) Request failed
SCRAPE_ERROR Anything else Scraping failed
NOT_AVAILABLE httpx / beautifulsoup4 not installed httpx and beautifulsoup4 not available

🔢 Decimal Format Remapping

The decimal_format parameter controls how the scraped text is parsed into a number:

Format Input Example Parsed Value
us (default) 1,234.56 1234.56
eu 1.234,56 1234.56

The parser first removes whitespace and the symbols € $ £ ¥ %. It then drops the group separator (, for US; . for EU, where , also becomes .) and converts to Decimal. Any other character — e.g. a currency code such as EUR next to the number — makes the conversion fail with PARSE_ERROR.

⚡ Caching & Performance

  • No response caching: Each get_current_value() call performs a fresh HTTP request. This is intentional — scraped data may change frequently and the provider cannot predict staleness.
  • No connection pooling across calls: each get_current_value() opens and closes its own httpx.AsyncClient.
  • Timeout handling: Configurable per-asset via timeout parameter. Default 30s prevents blocking on slow sites.

📋 Use Cases

  • Tracking the price of an asset from a financial news website.
  • Scraping data from a niche market data provider that doesn't have an API.
  • Tracking the value of a collectible from an auction site.

⚠️ Limitations

  • No Historical Data: supports_history = False. It can only fetch the current value.
  • Fragile: If the website's layout changes, the CSS selector may break. Use the probe endpoint to test before saving.
  • Requires Public Access: It cannot access pages that require a login, nor read prices that JavaScript adds after the page loads.
  • Rate limits: No built-in rate limiting. High-frequency sync may trigger the target site's anti-bot protection.