crankpy 0.1.1

Python Components with Generators - A Python wrapper for Crank.js bringing JSX-like syntax to PyScript

⚙️ Crank.py

Python Components with Generators - A Python wrapper for the Crank JavaScript framework, bringing modern component patterns to Python web development.

Built on the Crank.js framework

✨ Features

• 🐍 Pythonic Hyperscript - Clean template h.div["content"] syntax inspired by JSX
• 🔄 Generator Components - Natural state management using Python generators
• 🎨 Lifecycle Decorators - @ctx.refresh, @ctx.after, @ctx.cleanup
• 🔗 Props Loop - Reactive for props in ctx: pattern
• ⚡ Zero Build Step - Pure Python, runs anywhere PyScript runs
• 🌐 Browser Native - Works in PyScript, Pyodide, and Node.js environments

📦 Installation

PyScript (Browser)

<py-config>
{
    "packages": ["crankpy"],
    "js_modules": {
        "main": {
            "https://cdn.jsdelivr.net/npm/@b9g/crank@latest/crank.js": "crank_core",
            "https://cdn.jsdelivr.net/npm/@b9g/crank@latest/dom.js": "crank_dom"
        }
    }
}
</py-config>

Or use direct file loading:

<py-config>
{
    "files": {
        "https://raw.githubusercontent.com/bikeshaving/crankpy/main/crank/__init__.py": "crank/__init__.py",
        "https://raw.githubusercontent.com/bikeshaving/crankpy/main/crank/dom.py": "crank/dom.py"
    },
    "js_modules": {
        "main": {
            "https://cdn.jsdelivr.net/npm/@b9g/crank@latest/crank.js": "crank_core",
            "https://cdn.jsdelivr.net/npm/@b9g/crank@latest/dom.js": "crank_dom"
        }
    }
}
</py-config>

pip

pip install crankpy

🚀 Quick Start

Hello World

from crank import h, component
from crank.dom import renderer
from js import document

@component
def Greeting(ctx):
    for _ in ctx:
        yield h.div["Hello, Crank.py! ⚙️"]

renderer.render(h(Greeting), document.body)

Interactive Counter

@component
def Counter(ctx):
    count = 0
    
    @ctx.refresh
    def increment():
        nonlocal count
        count += 1
    
    @ctx.refresh  
    def decrement():
        nonlocal count
        count -= 1
    
    for _ in ctx:
        yield h.div[
            h.h2[f"Count: {count}"],
            h.button(onClick=increment)["+"],
            h.button(onClick=decrement)["-"]
        ]

Props Reassignment

@component
def UserProfile(ctx, props):
    for props in ctx:  # Props automatically update!
        user_id = props.user_id
        user = fetch_user(user_id)  # Fetches when props change
        
        yield h.div[
            h.img(src=user.avatar),
            h.h2[user.name],
            h.p[user.bio]
        ]

# Usage
h(UserProfile, user_id=123)

📖 Hyperscript Syntax Guide

Crank.py uses a clean, Pythonic hyperscript syntax:

HTML Elements

# Simple text content
h.div["Hello World"]
h.p["Some text"]

# With properties
h.input(type="text", value=text)
h.div(className="my-class")["Content"]

# Snake_case → kebab-case conversion
h.div(
    data_test_id="button",     # becomes data-test-id
    aria_hidden="true"         # becomes aria-hidden
)["Content"]

# Props spreading (explicit + spread)
h.button(className="btn", **userProps)["Click me"]
h.input(type="text", required=True, **formProps)

# Multiple dict merging (when needed)
h.div(**{**defaults, **themeProps, **userProps})["Content"]

# Nested elements
h.ul[
    h.li["Item 1"],
    h.li["Item 2"],
    h.li[
        "Item with ",
        h.strong["nested"],
        " content"
    ]
]

# Style objects (snake_case → kebab-case)
h.div(style={
    "background_color": "#f0f0f0",  # becomes background-color
    "border_radius": "5px"          # becomes border-radius
})["Styled content"]

# Reserved keywords with spreading
h.div(**{"class": "container", **userProps})["Content"]
# Or better: use className instead of class
h.div(className="container", **userProps)["Content"]

Components

# Component without props
h(MyComponent)

# Component with props
h(MyComponent, name="Alice", count=42)

# Component with children
h(MyComponent)[
    h.p["Child content"]
]

# Component with props and children
h(MyComponent, title="Hello")[
    h.p["Child content"]
]

Fragments

# Simple fragments - just use Python lists!
["Multiple", "children", "without", "wrapper"]
[h.div["Item 1"], h.div["Item 2"]]

# Fragment with props (when you need keys, etc.)
h("", key="my-fragment")["Child 1", "Child 2"]

# In context
h.div[
    h.h1["Title"],
    [h.p["Para 1"], h.p["Para 2"]],  # Simple fragment
    h.footer["Footer"]
]

🔄 Component Lifecycle

Component Signatures

Crank.py supports three component signatures:

# 1. Static components (no state)
@component
def Logo():
    return h.div["🔧 Crank.py"]

# 2. Context-only (internal state)
@component  
def Timer(ctx):
    start_time = time.time()
    for _ in ctx:
        elapsed = time.time() - start_time
        yield h.div[f"Time: {elapsed:.1f}s"]

# 3. Context + Props (reactive)
@component
def TodoItem(ctx, props):
    for props in ctx:  # New props each iteration
        todo = props.todo
        yield h.li[
            h.input(type="checkbox", checked=todo.done),
            h.span[todo.text]
        ]

Lifecycle Decorators

@component
def MyComponent(ctx):
    @ctx.refresh
    def handle_click():
        # Automatically triggers re-render
        pass
    
    @ctx.schedule  
    def before_render():
        # Runs before each render
        pass
    
    @ctx.after
    def after_render(node):
        # Runs after DOM update
        node.style.color = "blue"
    
    @ctx.cleanup
    def on_unmount():
        # Cleanup when component unmounts
        clear_interval(timer)
    
    for _ in ctx:
        yield h.div(onClick=handle_click)["Click me"]

🎯 Examples

Todo App

@component
def TodoApp(ctx):
    todos = []
    new_todo = ""
    
    @ctx.refresh
    def add_todo():
        nonlocal todos, new_todo
        if new_todo.strip():
            todos.append({"text": new_todo, "done": False})
            new_todo = ""
    
    @ctx.refresh
    def toggle_todo(index):
        nonlocal todos
        todos[index]["done"] = not todos[index]["done"]
    
    for _ in ctx:
        yield h.div[
            h.h1["Todo List"],
            h.input(
                type="text", 
                value=new_todo,
                oninput=lambda e: setattr(sys.modules[__name__], 'new_todo', e.target.value)
            ),
            h.button(onclick=add_todo)["Add"],
            h.ul[
                [h.li(key=i)[
                    h.input(
                        type="checkbox", 
                        checked=todo["done"],
                        onChange=lambda i=i: toggle_todo(i)
                    ),
                    h.span[todo["text"]]
                ] for i, todo in enumerate(todos)]
            ]
        ]

Real-time Clock

@component
def Clock(ctx):
    import asyncio
    
    async def update_time():
        while True:
            await asyncio.sleep(1)
            ctx.refresh()
    
    # Start the update loop
    asyncio.create_task(update_time())
    
    for _ in ctx:
        current_time = time.strftime("%H:%M:%S")
        yield h.div[
            h.strong["Current time: "],
            current_time
        ]

🧪 Testing

Run the test suite:

# Install dependencies
pip install pytest playwright

# Run tests
pytest tests/

🛠️ Development

# Clone the repository
git clone https://github.com/bikeshaving/crankpy.git crankpy
cd crankpy

# Install in development mode
pip install -e ".[dev]"

# Run examples
python -m http.server 8000
# Visit http://localhost:8000/examples/

🌟 Why Crank.py?

Python Web Development, Modernized

Traditional Python web frameworks use templates and server-side rendering. Crank.py brings component-based architecture to Python:

• 🧩 Reusable Components - Build UIs from composable pieces
• 🔄 Reactive Updates - Automatic re-rendering when state changes
• 🎯 Generator-Powered - Natural state management with Python generators
• 🌐 Browser-Native - Run Python directly in the browser via PyScript

Perfect for:

• 📱 PyScript Applications - Rich client-side Python apps
• 🎓 Educational Projects - Teaching web development with Python
• 🏗️ Prototyping - Rapid UI development without JavaScript
• 🔬 Data Visualization - Interactive Python data apps in the browser

📚 Learn More

• Crank.js Documentation - The underlying framework
• PyScript Guide - Running Python in browsers
• Examples - See Crank.py in action

🤝 Contributing

Contributions welcome! Please read our Contributing Guide first.

📄 License

MIT © 2024