A pure Python HTML5 parser that just works.
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Project description
JustHTML
A pure Python HTML5 parser that just works. No C extensions to compile. No system dependencies to install. No complex API to learn.
Why use JustHTML?
1. Just... Correct ✅
It implements the official WHATWG HTML5 specification exactly. If a browser can parse it, JustHTML can parse it. It handles all the complex error-handling rules that browsers use.
- Verified Compliance: Passes all 8,500+ tests in the official html5lib-tests suite (used by browser vendors).
- 100% Coverage: Every line and branch of code is covered by integration tests.
- Fuzz Tested: Has parsed 3 million randomized broken HTML documents to ensure it never crashes or hangs (see benchmarks/fuzz.py).
- Living Standard: It tracks the living standard, not a snapshot from 2012.
2. Just... Python 🐍
JustHTML has zero dependencies. It's pure Python.
- Just Install: No C extensions to compile, no system libraries (like libxml2) required. Works on PyPy, WASM (Pyodide) (yes, it's in the test matrix), and anywhere Python runs.
- No dependency upgrade hassle: Some libraries depend on a large set of libraries, all which require upgrades to avoid security issues.
- Debuggable: It's just Python code. You can step through it with a debugger to understand exactly how your HTML is being parsed.
- Returns plain python objects: Other parsers return lxml or etree trees which means you have another API to learn. JustHTML returns a set of nested objects you can iterate over. Simple.
3. Just... Query 🔍
Find elements with CSS selectors. Just one method to learn - query() - and it uses CSS syntax you already know.
doc.query("div.container > p.intro") # Familiar CSS syntax
doc.query("#main, .sidebar") # Selector groups
doc.query("li:nth-child(2n+1)") # Pseudo-classes
4. Just... Fast Enough ⚡
If you need to parse terabytes of data, use a C or Rust parser (like html5ever). They are 10x-20x faster.
But for most use cases, JustHTML is fast enough. It parses the Wikipedia homepage in ~0.1s. It is the fastest pure-Python HTML5 parser available, outperforming html5lib and BeautifulSoup.
Comparison to other parsers
| Parser | HTML5 Compliance | Pure Python? | Speed | Query API | Notes |
|---|---|---|---|---|---|
| JustHTML | ✅ 100% | ✅ Yes | ⚡ Fast | ✅ CSS selectors | It just works. Correct, easy to install, and fast enough. |
html5lib |
🟡 88% | ✅ Yes | 🐢 Slow | ❌ None | The reference implementation. Very correct but quite slow. |
html5_parser |
🟡 84% | ❌ No | 🚀 Very Fast | 🟡 XPath (lxml) | C-based (Gumbo). Fast and mostly correct. |
selectolax |
🟡 68% | ❌ No | 🚀 Very Fast | ✅ CSS selectors | C-based (Lexbor). Very fast but less compliant. |
BeautifulSoup |
🔴 4% | ✅ Yes | 🐢 Slow | 🟡 Custom API | Wrapper around html.parser. Not spec compliant. |
html.parser |
🔴 4% | ✅ Yes | ⚡ Fast | ❌ None | Standard library. Chokes on malformed HTML. |
lxml |
🔴 1% | ❌ No | 🚀 Very Fast | 🟡 XPath | C-based (libxml2). Fast but not HTML5 compliant. |
Compliance scores from running the html5lib-tests suite (1,743 tree-construction tests). See benchmarks/correctness.py.
Installation
Requires Python 3.10 or later.
pip install justhtml
Example usage
Python API
from justhtml import JustHTML
html = "<html><body><div id='main'><p>Hello, <b>world</b>!</p></div></body></html>"
doc = JustHTML(html)
# 1. Traverse the tree
# The tree is made of SimpleDomNode objects.
# Each node has .name, .attrs, .children, and .parent
root = doc.root # #document
html_node = root.children[0] # html
body = html_node.children[1] # body (children[0] is head)
div = body.children[0] # div
print(f"Tag: {div.name}")
print(f"Attributes: {div.attrs}")
# 2. Query with CSS selectors
# Find elements using familiar CSS selector syntax
paragraphs = doc.query("p") # All <p> elements
main_div = doc.query("#main")[0] # Element with id="main"
bold = doc.query("div > p b") # <b> inside <p> inside <div>
# 3. Pretty-print HTML
# You can serialize any node back to HTML
print(div.to_html())
# Output:
# <div id="main">
# <p>
# Hello,
# <b>world</b>
# !
# </p>
# </div>
# 4. Streaming API (extremely fast and memory efficient)
# For massive files or when you don't need the full DOM tree.
# NOTE: Does not build a tree and _only_ runs the html5-compatible tokenizer
from justhtml import stream
for event, data in stream(html):
if event == "start":
tag, attrs = data
print(f"Start: {tag} with {attrs}")
elif event == "text":
print(f"Text: {data}")
elif event == "end":
print(f"End: {data}")
# 5. Strict mode (reject malformed HTML)
# Raises an exception on the first parse error with source highlighting
try:
doc = JustHTML("<html><p>Hello", strict=True)
except Exception as e:
print(e)
# Output (Python 3.11+):
# File "<html>", line 1
# <html><p>Hello
# ^
# StrictModeError: Expected closing tag </p> but reached end of file
Supported CSS Selectors
JustHTML supports a comprehensive subset of CSS selectors:
| Selector | Example | Description |
|---|---|---|
| Tag | div |
Elements by tag name |
| Class | .intro |
Elements with class |
| ID | #main |
Element with ID |
| Universal | * |
All elements |
| Attribute | [href] |
Elements with attribute |
| Attr value | [type="text"] |
Exact attribute match |
| Attr prefix | [href^="https"] |
Attribute starts with |
| Attr suffix | [href$=".pdf"] |
Attribute ends with |
| Attr contains | [href*="example"] |
Attribute contains |
| Descendant | div p |
<p> inside <div> |
| Child | div > p |
Direct child |
| Adjacent | h1 + p |
Immediately after |
| Sibling | h1 ~ p |
Any sibling after |
| First child | :first-child |
First child element |
| Last child | :last-child |
Last child element |
| Nth child | :nth-child(2n+1) |
Nth child (odd, even, formula) |
| Not | :not(.hidden) |
Negation |
| Groups | h1, h2, h3 |
Multiple selectors |
Command Line Interface
You can also use JustHTML from the command line to pretty-print HTML files:
# Parse a file
python -m justhtml index.html
# Parse from stdin (great for piping)
curl -s https://example.com | python -m justhtml -
Develop locally and run the tests
-
Clone the repository:
git clone git@github.com:EmilStenstrom/justhtml.git cd justhtml
-
Install the library locally:
pip install -e ".[dev]"
-
Run the tests:
python run_tests.pyFor verbose output showing diffs on failures:
python run_tests.py -v
-
Run the benchmarks:
python benchmarks/performance.py
License
MIT. Free to use both for commercial and non-commercial use.
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