YDNATL

YDNATL (You Don't Need Another Template Language) is a Python library that lets you build HTML using simple Python classes. It's great for apps that need HTML generation while skipping the hassle of writing it by hand or using a templating engine.

✓ Declarative syntax for building HTML documents (like Flutter)
✓ Easy to read and write
✓ Supports all HTML5 elements
✓ JSON serialization/deserialization for saving and loading UI structures
✓ Pretty printing with indentation for readable HTML
✓ CSS style helpers for easy inline styling
✓ External stylesheet system with theming and BEM support
✓ Method chaining for fluent interfaces
✓ Context manager support for clean nesting
✓ Fragment support for wrapper-free grouping
✓ HTML parsing to convert raw HTML strings into YDNATL elements
✓ Lightweight
✓ Extremely fast
✓ Fully customisable
✓ Compose HTML efficiently
✓ Lean & clean Python with no dependencies
✓ LLM Compatible

Requirements

Python 3.8 or higher is required.

Installation

pip install ydnatl

Usage

from ydnatl import *

# Create a simple HTML document
page = HTML(
    Head(
        Title("My Page")
    ),
    Body(
        Div(
            H1("Hello, World!"),
            Paragraph("This is a test document.")
        )
    )
)

print(page.render())

This code will produce:

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <title>My Page</title>
  </head>
  <body>
    <div>
      <h1>Hello, World!</h1>
      <p>This is a test document.</p>
    </div>
  </body>
</html>

Dynamic Composition

from ydnatl import *

# Dynamic content based on conditions
day_of_week = "Monday"  # Example variable

html = HTML()
header = Head()
body = Body()

body.append(
    Div(
        H1("My Headline"),
        Paragraph("Basic paragraph element"),
    )
)

if day_of_week == "Monday": 
    header.append(Title("Unfortunately, it's Monday!"))
else:
    header.append(Title("Great! It's no longer Monday!"))

html.append(header)
html.append(body)

print(html.render())

All element classes are subclasses of HTMLElement. The parent class provides all of the inherited functionality to generate the individual tags. Keyword arguments passed to element constructors will be converted to attributes on the HTML elements being generated.

Working with Attributes

from ydnatl import *

# Add attributes via constructor
div = Div(id="my-div", class_name="container", data_value="123")

# Add attributes after creation
div.add_attribute("role", "main")
div.add_attributes([("aria-label", "Main content"), ("tabindex", "0")])

# HTML output: <div id="my-div" class="container" data-value="123" role="main" aria-label="Main content" tabindex="0"></div>

Pretty Printing

YDNATL supports pretty printing with automatic indentation for readable HTML output:

from ydnatl import *

page = HTML(
    Head(Title("My Page")),
    Body(
        Div(
            H1("Hello, World!"),
            Paragraph("This is a paragraph.")
        )
    )
)

# Compact output (default)
print(page.render())
# Output: <!DOCTYPE html><html lang="en" dir="ltr"><head><title>My Page</title></head>...

# Pretty output with indentation
print(page.render(pretty=True))
# Output:
# <!DOCTYPE html>
# <html lang="en" dir="ltr">
#   <head>
#     <title>My Page</title>
#   </head>
#   <body>
#     <div>
#       <h1>Hello, World!</h1>
#       <p>This is a paragraph.</p>
#     </div>
#   </body>
# </html>

Pretty printing is perfect for:

Development and debugging
Generating human-readable HTML files
Documentation and tutorials
Inspecting complex structures

CSS Style Helpers

YDNATL provides convenient methods for working with inline CSS styles:

from ydnatl import *

# Create element and add styles
div = Div("Styled content")

# Add single style
div.add_style("color", "blue")
div.add_style("font-size", "16px")

# Add multiple styles at once
div.add_styles({
    "background-color": "#f0f0f0",
    "padding": "20px",
    "margin": "10px",
    "border-radius": "5px"
})

# Get a specific style value
color = div.get_style("color")  # Returns "blue"

# Remove a style
div.remove_style("margin")

# Result: <div style="color: blue; font-size: 16px; background-color: #f0f0f0; padding: 20px; border-radius: 5px">Styled content</div>

External Stylesheet and Theming

YDNATL includes a powerful styling system for managing external stylesheets, themes, and reusable component styles. This is perfect for building larger applications where you want to separate styles from markup.

Basic StyleSheet Usage

from ydnatl import *
from ydnatl.styles import CSSStyle, StyleSheet

# Create a stylesheet
stylesheet = StyleSheet()

# Register reusable styles
btn_primary = stylesheet.register("btn-primary", CSSStyle(
    background_color="#007bff",
    color="white",
    padding="10px 20px",
    border_radius="5px",
    border="none",
    cursor="pointer",
    _hover=CSSStyle(background_color="#0056b3")  # Pseudo-selector
))

# Use in HTML
page = HTML(
    Head(
        Title("My Page"),
        Style(stylesheet.render())  # Insert generated CSS
    ),
    Body(
        Button("Click Me", class_name=btn_primary)
    )
)

Theming Support

YDNATL includes three preset themes (Modern, Classic, Minimal) with full CSS variable support:

from ydnatl.styles import Theme, StyleSheet, CSSStyle

# Use a preset theme
theme = Theme.modern()  # or Theme.classic() or Theme.minimal()

# Create stylesheet with theme
stylesheet = StyleSheet(theme=theme)

# Register styles using theme variables
btn = stylesheet.register("btn", CSSStyle(
    background_color="var(--color-primary)",
    color="var(--color-white)",
    padding="var(--spacing-md)",
    border_radius="6px",
    _hover=CSSStyle(background_color="var(--color-primary-dark)")
))

card = stylesheet.register("card", CSSStyle(
    background_color="var(--color-white)",
    padding="var(--spacing-lg)",
    border_radius="8px",
    box_shadow="0 1px 3px rgba(0, 0, 0, 0.1)"
))

BEM Naming Convention

Built-in support for BEM (Block Element Modifier) naming:

from ydnatl.styles import StyleSheet, CSSStyle

stylesheet = StyleSheet()

# Register with BEM naming
card = stylesheet.register_bem("card", style=CSSStyle(
    background="white",
    padding="20px"
))

card_header = stylesheet.register_bem("card", element="header", style=CSSStyle(
    font_weight="bold"
))

card_featured = stylesheet.register_bem("card", modifier="featured", style=CSSStyle(
    border="2px solid blue"
))

# Generates: .card, .card__header, .card--featured

Responsive Breakpoints

Add responsive styles with breakpoint support:

from ydnatl.styles import CSSStyle, StyleSheet

stylesheet = StyleSheet()

container = stylesheet.register("container", CSSStyle(
    padding="10px",
    _sm=CSSStyle(padding="15px", max_width="640px"),
    _md=CSSStyle(padding="20px", max_width="768px"),
    _lg=CSSStyle(padding="30px", max_width="1024px")
))

# Generates media queries automatically

Combining with Inline Styles

You can mix stylesheet classes with inline style overrides:

# Register base style
btn = stylesheet.register("btn", CSSStyle(
    padding="10px 20px",
    border_radius="5px"
))

# Use base class + inline overrides
Button("Custom", class_name=btn).add_styles({
    "background-color": "#ff0000",
    "font-size": "18px"
})

Key Features:

Snake_case to kebab-case conversion (background_color → background-color)
Pseudo-selector support (:hover, :active, :focus, etc.)
Responsive breakpoints with media queries
Theme system with CSS variables
BEM naming convention support
JSON serialization for saving/loading styles
Combines seamlessly with existing inline styles

See the examples/stylesheet_example.py file for complete working examples.

Method Chaining

All builder methods return self, enabling fluent method chaining:

from ydnatl import *

# Chain multiple operations together
container = (Div()
    .add_attribute("id", "main-container")
    .add_attribute("class", "wrapper")
    .add_style("background", "#fff")
    .add_styles({"padding": "20px", "margin": "0 auto"})
    .append(H1("Welcome"))
    .append(Paragraph("This is the main content."))
    .append(Paragraph("Another paragraph here.")))

print(container.render())

Chainable methods:

append() - Add children
prepend() - Add children at the beginning
add_attribute() - Add single attribute
add_attributes() - Add multiple attributes
remove_attribute() - Remove an attribute
add_style() - Add single CSS style
add_styles() - Add multiple CSS styles
remove_style() - Remove a CSS style
clear() - Remove all children
remove_all() - Remove children matching a condition

Context Manager Support

Use elements as context managers for cleaner, more intuitive nesting:

from ydnatl import *

# Using context managers
with Div(id="container", class_name="main") as container:
    with Section(class_name="content") as section:
        section.append(H1("Title"))
        section.append(Paragraph("Content goes here"))

    container.append(section)
    container.append(Footer(Paragraph("Footer text")))

print(container.render())

Fragment Support

Use Fragment to group elements without adding a wrapper tag:

from ydnatl import *

# Without Fragment - adds extra div wrapper
content = Div(
    H1("Title"),
    Paragraph("Content")
)
# Output: <div><h1>Title</h1><p>Content</p></div>

# With Fragment - no wrapper tag
content = Fragment(
    H1("Title"),
    Paragraph("Content")
)
# Output: <h1>Title</h1><p>Content</p>

# Perfect for conditional rendering
def render_items(items, show_header=True):
    fragment = Fragment()

    if show_header:
        fragment.append(H2("Items List"))

    for item in items:
        fragment.append(Paragraph(item))

    return fragment

# Use in parent element
page = Div(
    render_items(["Item 1", "Item 2", "Item 3"], show_header=True)
)
# Output: <div><h2>Items List</h2><p>Item 1</p><p>Item 2</p><p>Item 3</p></div>

Fragment use cases:

Conditional rendering without wrapper divs
Returning multiple elements from functions
List composition and iteration
Cleaner component architecture

HTML Parsing

YDNATL can parse raw HTML strings and convert them into YDNATL elements. This is useful for importing existing HTML, migrating from other tools, or working with HTML from external sources.

from ydnatl import from_html, HTMLElement

# Parse a single HTML element
html_string = '<div class="container"><h1>Hello World</h1><p>Welcome to YDNATL</p></div>'
element = from_html(html_string)

# Now you can work with it like any YDNATL element
element.add_style("padding", "20px")
element.append(Paragraph("Added via YDNATL"))

print(element.render())
# Output: <div class="container" style="padding: 20px"><h1>Hello World</h1><p>Welcome to YDNATL</p><p>Added via YDNATL</p></div>

# Alternative: use the class method
element = HTMLElement.from_html(html_string)

Parsing HTML fragments (multiple root elements):

from ydnatl import from_html

# HTML with multiple root elements
html_fragment = '''
<h1>Welcome</h1>
<p>First paragraph</p>
<p>Second paragraph</p>
'''

# Parse as fragment (returns list of elements)
elements = from_html(html_fragment, fragment=True)

# Work with each element
for el in elements:
    print(el.tag, el.text)
# Output:
# h1 Welcome
# p First paragraph
# p Second paragraph

# Combine with other YDNATL features
container = Div()
for el in elements:
    container.append(el)

print(container.render())
# Output: <div><h1>Welcome</h1><p>First paragraph</p><p>Second paragraph</p></div>

Features:

Handles all HTML5 elements including self-closing tags (br, img, hr, etc.)
Preserves attributes, including data-* attributes
Converts class attribute to class_name automatically
Supports nested structures of any depth
Handles HTML entities and special characters
No external dependencies (uses Python's built-in html.parser)

Use cases:

Import existing HTML into your website builder
Migrate from other HTML generation tools
Parse HTML templates from external sources
Convert HTML snippets to YDNATL for manipulation
Testing and validation workflows
Combining static HTML with dynamic YDNATL generation

JSON Serialization

YDNATL supports JSON serialization and deserialization, making it perfect for drag-and-drop website builders, saving UI states, or transmitting page structures over APIs.

from ydnatl import *

# Build a page structure
page = Div(id="page", class_name="container")
page.append(
    H1("Welcome"),
    Section(
        Paragraph("This is a paragraph"),
        Paragraph("Another paragraph", class_name="highlight")
    )
)

# Serialize to JSON (for saving/storing)
json_data = page.to_json(indent=2)
print(json_data)

# Later... deserialize from JSON (for loading)
from ydnatl.core.element import HTMLElement
restored_page = HTMLElement.from_json(json_data)

# Generate HTML (output will be identical)
print(str(restored_page))

The JSON format is simple and clean:

{
  "tag": "div",
  "self_closing": false,
  "attributes": {
    "id": "page",
    "class": "container"
  },
  "text": "",
  "children": []
}

Use cases:

Save/load website layouts to/from a database
Implement undo/redo functionality
Store pre-built templates as JSON
Version control for page structures
API communication between frontend and backend
Drag-and-drop website builders

Great For

CLI tools
Drag-and-drop website builders
Site builders with save/load functionality
Web frameworks
Alternative to heavy template engines
Static site generators
Documentation generators
LLM's and AI tooling that generate interfaces dynamically
Creating frontends for headless platforms (CMS/CRM etc)
Applications requiring UI state serialization

LLM Guide

For AI assistants and code generation tools, we provide a comprehensive technical reference in LLM_GUIDE.md with:

Complete API documentation with exact method signatures
Type hints and return values for all methods
10 common patterns with code examples
Error handling and security best practices
Quick reference cheat sheet

Examples

FastAPI

from fastapi import FastAPI
from ydnatl import *

app = FastAPI()

@app.get("/")
async def root():
    return HTML(
        Head(
            Title("My Page")
        ),
        Body(
            Section(
                H1("Hello, World!"),
                Paragraph("This is a test document.")
            )
        )
    )

Django

from django.http import HttpResponse
from ydnatl import *

def index(request):
    return HttpResponse(HTML(
        Head(
            Title("My Page"),
            Meta(charset="utf-8"),
            Meta(name="viewport", content="width=device-width, initial-scale=1.0"),
            HtmlLink(rel="stylesheet", href="style.css"),
            Script(src="script.js")
        ),
        Body(
            Section(
                H1("Hello, World!"),
                Paragraph("This is a paragraph."),
                Paragraph("This is another paragraph.")
            )
        )
    ))

Flask

from flask import Flask
from ydnatl import *

app = Flask(__name__)

@app.route("/")
def index():
    return HTML(
        Head(
            Title("My Page")
        ),
        Body(
            Section(
                H1("Hello, World!"),
                Paragraph("This is a test document.")
            )
        )
    )

Test Coverage

YDNATL has full test coverage. To run the tests locally, use:

pytest

Element Methods:

Element Manipulation:

instance.prepend() - Prepend children (returns self for chaining)
instance.append() - Append children (returns self for chaining)
instance.filter() - Filter children by condition
instance.remove_all() - Remove children matching condition (returns self for chaining)
instance.clear() - Remove all children (returns self for chaining)
instance.pop() - Remove and return child at index
instance.first() - Get first child
instance.last() - Get last child
instance.replace_child() - Replace child at index
instance.clone() - Deep copy of element
instance.find_by_attribute() - Find child by attribute value
instance.count_children() - Count direct children

Attribute Management:

instance.add_attribute() - Add single attribute (returns self for chaining)
instance.add_attributes() - Add multiple attributes (returns self for chaining)
instance.remove_attribute() - Remove attribute (returns self for chaining)
instance.get_attribute() - Get attribute value
instance.has_attribute() - Check if attribute exists
instance.get_attributes() - Get all or specific attributes
instance.generate_id() - Generate unique ID if not present

CSS Style Management:

instance.add_style() - Add single CSS style (returns self for chaining)
instance.add_styles() - Add multiple CSS styles (returns self for chaining)
instance.get_style() - Get specific style value
instance.remove_style() - Remove CSS style (returns self for chaining)

Rendering:

instance.render(pretty=False) - Render to HTML string (pretty=True for indented output)
instance.to_dict() - Convert to dictionary
instance.to_json(indent=None) - Serialize to JSON string
HTMLElement.from_dict(data) - Reconstruct from dictionary (class method)
HTMLElement.from_json(json_str) - Reconstruct from JSON string (class method)
HTMLElement.from_html(html_str, fragment=False) - Parse HTML string to YDNATL element(s) (class method)
from_html(html_str, fragment=False) - Parse HTML string to YDNATL element(s) (function)

Events

instance.on_load()
instance.on_before_render()
instance.on_after_render()
instance.on_unload()

Element Properties

instance.tag
instance.children
instance.text
instance.attributes
instance.self_closing

Modules

Module	Purpose	Key Elements
ydnatl.tags.form	Common HTML form elements	Form, Input, Button, Select, Textarea
ydnatl.tags.html	Structural HTML document elements	HTML, Head, Body, Title, Meta, Script
ydnatl.tags.layout	Layout related HTML tags	Div, Section, Header, Nav, Footer, Main
ydnatl.tags.lists	HTML list elements	UnorderedList, OrderedList, ListItem
ydnatl.tags.media	Media related HTML elements	Image, Video, Audio, Figure, Canvas
ydnatl.tags.table	HTML table elements	Table, TableRow, TableHeaderCell, TableDataCell
ydnatl.tags.text	HTML text elements	H1-H6, Paragraph, Span, Strong, Em

Importing

Instead of importing the entire module, you can selectively use only the elements you need like this:

# Instead of importing everything
from ydnatl import *

# Import selectively for better performance and clarity
from ydnatl.tags.form import Form, Button, Input
from ydnatl.tags.html import HTML, Head, Body, Title
from ydnatl.tags.layout import Div, Section
from ydnatl.tags.text import H1, Paragraph

ydnatl.tags.lists

UnorderedList()
OrderedList()
ListItem()
Datalist()
DescriptionDetails()
DescriptionList()
DescriptionTerm()

Creating your own elements or components

from ydnatl import *

class MyTag(HTMLElement):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **{**kwargs, "tag": "mytag"})

        self.add_attributes([
            ("id", "mycustomid"),
            ("aria-controls", "menu"),
        ])

    def on_load(self) -> None:
        print("The on_load event has been called")

    def on_before_render(self) -> None:
        print("The on_before_render event has been called")

    def on_after_render(self) -> None:
        print("The on_after_render event has been called")


mytag = MyTag(
    Div(
        Paragraph("Hello World!")
    )
)

print(mytag.render())

This will produce:

<mytag id="mycustomid" aria-controls="menu">
  <div>
    <p>Hello World!</p>
  </div>
</mytag>

You can use the event callbacks or properties/methods directly to load further child elements, fetch data or any other programmatic task to enrich or construct your tag on loading, render or even after render.

You can take this further and construct an entire page as a component where everything needed for the page is contained within the element class itself. This is a great way to build websites.

Contributions

Contributions, suggestions and improvements are all welcome.

Developing YDNATL

Create a virtual environment

python3 -m venv .venv 
source .venv/bin/activate  # On Windows: .venv\Scripts\activate
pip install --upgrade pip

Install the dev dependencies:

pip install ".[dev]"

Run the tests:

pytest

When you are happy with your changes, create a merge request.

License

Please see LICENSE for licensing details.

Author

github.com/sn

Name		Name	Last commit message	Last commit date
Latest commit History 72 Commits
.github/workflows		.github/workflows
examples		examples
src/ydnatl		src/ydnatl
tests		tests
.gitignore		.gitignore
LICENSE		LICENSE
LLM_GUIDE.md		LLM_GUIDE.md
README.md		README.md
pyproject.toml		pyproject.toml
requirements.txt		requirements.txt

License

sn/ydnatl

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YDNATL

Requirements

Installation

Usage

Dynamic Composition

Working with Attributes

Pretty Printing

CSS Style Helpers

External Stylesheet and Theming

Basic StyleSheet Usage

Theming Support

BEM Naming Convention

Responsive Breakpoints

Combining with Inline Styles

Method Chaining

Context Manager Support

Fragment Support

HTML Parsing

JSON Serialization

Great For

LLM Guide

Examples

FastAPI

Django

Flask

Test Coverage

Element Methods:

Events

Element Properties

Modules

Importing

ydnatl.tags.form

ydnatl.tags.html

ydnatl.tags.layout

ydnatl.tags.lists

ydnatl.tags.media

ydnatl.tags.table

ydnatl.tags.text

Creating your own elements or components

Contributions

Developing YDNATL

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