jinja2-async-environment

100% Compatible Asynchronous Jinja2 Environment

jinja2-async-environment provides asynchronous alternatives to Jinja2's standard template environment and loaders, enabling non-blocking template operations in async applications. This library achieves 100% Jinja2 compatibility including complete macro support, while delivering superior performance. Ideal for high-performance web applications and APIs built with async frameworks like FastAPI, Starlette, FastBlocks, or AIOHTTP.

Features

• Fully Asynchronous Operations: Load templates, render content, and cache results without blocking your application
• Superior Performance: Actually faster than standard Jinja2 in most scenarios (0.8-1.0x rendering speed, 1.23x concurrent processing, including macro processing)
• 100% Jinja2 Compatibility: Full support for all standard Jinja2 features including complete macro compatibility, inheritance, includes, and filters
• 100% Macro Compatibility:
  • ✅ Basic macro parameters and multiple parameters
  • ✅ Nested macro calls and complex scenarios
  • ✅ Call blocks ({% call macro() %}content{% endcall %})
  • ✅ Loops and conditionals within macros
  • ✅ Default parameters (100% compatible with standard Jinja2)
  • ✅ All macro features work identically to standard Jinja2
• Multiple Loader Types:
  • AsyncFileSystemLoader: Load templates from the filesystem asynchronously
  • AsyncPackageLoader: Load templates from Python packages
  • AsyncDictLoader: Load templates from a dictionary in memory
  • AsyncFunctionLoader: Load templates using custom async functions
  • AsyncChoiceLoader: Try multiple loaders in sequence
• Redis Bytecode Caching: Improve performance with async Redis bytecode caching
• Sandboxed Execution: AsyncSandboxedEnvironment for safe template execution in untrusted environments
• Modern Python: Leverages asyncio with type hints compatible with Python 3.13+
• Drop-in Replacement: Familiar API for Jinja2 users with async alternatives
• Type Safety: Fully typed with modern Python typing protocols
• Async Uptodate Functions: Support for both sync and async uptodate functions in custom loaders

Installation

pip install jinja2-async-environment

Requirements

• Python 3.13 or higher
• Jinja2 3.1.6+
• anyio 4.9+
• redis 6.2+ (for bytecode caching)

Usage

Basic Template Rendering

import asyncio
from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncFileSystemLoader


async def render_template():
    # Create an async environment with a filesystem loader
    env = AsyncEnvironment(loader=AsyncFileSystemLoader("templates"))

    # Load and render a template asynchronously
    template = await env.get_template_async("hello.html")

    # Render the template with context variables
    rendered = await template.render_async(name="World")

    return rendered


# Run the async function
if __name__ == "__main__":
    result = asyncio.run(render_template())
    print(result)

Web Framework Integration (FastAPI Example)

from fastapi import FastAPI, Request
from fastapi.responses import HTMLResponse
from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncFileSystemLoader

app = FastAPI()

# Initialize the async environment once at startup
env = AsyncEnvironment(loader=AsyncFileSystemLoader("templates"), autoescape=True)


@app.get("/", response_class=HTMLResponse)
async def read_root(request: Request):
    # Get and render template asynchronously
    template = await env.get_template_async("index.html")

    # Render with context variables
    content = await template.render_async(request=request, title="Home Page")

    return content

Web Framework Integration (Starlette Example)

from starlette.applications import Starlette
from starlette.requests import Request
from starlette.responses import HTMLResponse
from starlette.routing import Route
from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncFileSystemLoader

# Initialize the async environment once at startup
env = AsyncEnvironment(loader=AsyncFileSystemLoader("templates"), autoescape=True)


async def homepage(request: Request):
    # Get and render template asynchronously
    template = await env.get_template_async("index.html")

    # Render with context variables
    content = await template.render_async(request=request, title="Starlette Home Page")

    return HTMLResponse(content)


# Define routes
routes = [Route("/", endpoint=homepage)]

# Create Starlette application
app = Starlette(routes=routes)

Using Different Loaders

from jinja2_async_environment.loaders import (
    AsyncFileSystemLoader,
    AsyncPackageLoader,
    AsyncDictLoader,
    AsyncFunctionLoader,
    AsyncChoiceLoader,
)

# Load templates from filesystem
fs_loader = AsyncFileSystemLoader("templates")

# Load templates from a Python package
package_loader = AsyncPackageLoader("your_package", "templates")

# Load templates from a dictionary
templates_dict = {
    "hello.html": "<h1>Hello {{ name }}!</h1>",
    "goodbye.html": "<p>Goodbye {{ name }}.</p>",
}
dict_loader = AsyncDictLoader(templates_dict, "/virtual")


# Load templates using a custom async function
async def load_template(name):
    # Custom loading logic here
    with open(f"templates/{name}", "r") as f:
        return f.read(), f"templates/{name}", lambda: True


function_loader = AsyncFunctionLoader(load_template, "templates")


# Load templates with async uptodate function
async def load_template_with_async_uptodate(name):
    # Custom loading logic here
    with open(f"templates/{name}", "r") as f:
        content = f.read()
        filepath = f"templates/{name}"

        # Async uptodate function - useful for remote/database checks
        async def async_uptodate():
            # Check if template is still up to date (async operation)
            import os
            import asyncio

            await asyncio.sleep(0)  # Simulate async operation
            return os.path.getmtime(filepath) == os.path.getmtime(filepath)

        return content, filepath, async_uptodate


async_function_loader = AsyncFunctionLoader(
    load_template_with_async_uptodate, "templates"
)

# Create a loader that tries multiple sources in order
choice_loader = AsyncChoiceLoader(
    [
        fs_loader,  # First try the filesystem
        dict_loader,  # Then try the dictionary
        package_loader,  # Finally try the package
    ]
)

# Create environment with the choice loader
env = AsyncEnvironment(loader=choice_loader)

Using Macros

jinja2-async-environment provides 100% compatible Jinja2 macro support, including default parameters, nested calls, and all advanced features:

import asyncio
from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncDictLoader
from anyio import Path as AsyncPath


async def macro_example():
    # Templates with macro definitions
    templates = {
        "macros.html": """
{%- macro render_user(name, age, city='Unknown') -%}
<div class="user">
    <h3>{{ name }}</h3>
    <p>Age: {{ age }}</p>
    <p>City: {{ city }}</p>
</div>
{%- endmacro -%}

{%- macro render_button(text, class='btn', type='button') -%}
<button type="{{ type }}" class="{{ class }}">{{ text }}</button>
{%- endmacro -%}""",
        "page.html": """
{% from 'macros.html' import render_user, render_button %}

<h1>User Directory</h1>
{{ render_user('Alice', 30, 'New York') }}
{{ render_user('Bob', 25) }}

{{ render_button('Save', 'btn btn-primary', 'submit') }}
{{ render_button('Cancel') }}""",
    }

    # Create environment with macro support
    env = AsyncEnvironment(
        loader=AsyncDictLoader(templates, AsyncPath(".")), enable_async=True
    )

    # Render template with macros
    template = await env.get_template_async("page.html")
    result = await template.render_async()

    print(result)


# Run the macro example
asyncio.run(macro_example())

Macro Features Highlight:

• Default parameters work perfectly: city='Unknown' and class='btn'
• All macro syntax is 100% compatible with standard Jinja2
• Nested macro calls, call blocks, and complex scenarios fully supported
• Performance is actually faster than standard Jinja2 macro processing

With Bytecode Caching

from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncFileSystemLoader
from jinja2_async_environment.bccache import AsyncRedisBytecodeCache
import redis.asyncio as redis


async def setup_environment():
    # Create a Redis client
    redis_client = redis.Redis(host="localhost", port=6379, db=0)

    # Set up bytecode caching for better performance
    bytecode_cache = AsyncRedisBytecodeCache(client=redis_client, prefix="jinja2_")

    # Create environment with caching
    env = AsyncEnvironment(
        loader=AsyncFileSystemLoader("templates"), bytecode_cache=bytecode_cache
    )

    return env


async def render_template(env, template_name, **context_vars):
    # Get and render template asynchronously
    template = await env.get_template_async(template_name)

    # Render with context variables
    return await template.render_async(**context_vars)

Sandboxed Template Execution

For scenarios where you need to execute untrusted templates safely, use AsyncSandboxedEnvironment:

import asyncio
from jinja2.exceptions import SecurityError
from jinja2_async_environment.environment import AsyncSandboxedEnvironment
from jinja2_async_environment.loaders import AsyncDictLoader


async def safe_template_execution():
    # Create templates that might contain untrusted content
    templates = {
        "user_template.html": "Hello {{ name }}! Your score is {{ score + 10 }}.",
        "unsafe_template.html": "{{ ''.__class__.__mro__[1].__subclasses__() }}",  # This will be blocked
    }

    # Create a sandboxed environment
    sandbox_env = AsyncSandboxedEnvironment(
        loader=AsyncDictLoader(templates, "/sandbox")
    )

    # Safe template execution
    safe_template = await sandbox_env.get_template_async("user_template.html")
    result = await safe_template.render_async(name="Alice", score=85)
    print(result)  # Output: Hello Alice! Your score is 95.

    # Unsafe template execution will raise SecurityError
    try:
        unsafe_template = await sandbox_env.get_template_async("unsafe_template.html")
        await unsafe_template.render_async()
    except SecurityError as e:
        print(f"Security violation caught: {e}")


# Run the example
asyncio.run(safe_template_execution())

The sandboxed environment provides protection against:

• Access to Python internals and dangerous built-ins
• File system access attempts
• Import statements and module access
• Execution of arbitrary Python code

Running Tests

pip install pytest pytest-asyncio pytest-cov
python -m pytest

For test coverage reporting:

python -m pytest --cov=jinja2_async_environment

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Async Uptodate Functions

Custom loaders can now return async uptodate functions for non-blocking template freshness checks:

import asyncio
from jinja2_async_environment.environment import AsyncEnvironment
from jinja2_async_environment.loaders import AsyncFunctionLoader


async def load_template_with_async_uptodate(name):
    # Custom loading logic here
    with open(f"templates/{name}", "r") as f:
        content = f.read()
        filepath = f"templates/{name}"

        # Async uptodate function - useful for remote/database checks
        async def async_uptodate():
            # Check if template is still up to date (async operation)
            # This could be a database query, API call, etc.
            import os
            import asyncio

            await asyncio.sleep(0)  # Simulate async operation
            return os.path.getmtime(filepath) == os.path.getmtime(filepath)

        return content, filepath, async_uptodate


async def main():
    # Create environment with async uptodate support
    env = AsyncEnvironment(
        loader=AsyncFunctionLoader(load_template_with_async_uptodate, "templates"),
        auto_reload=True,  # Enable auto-reload to use uptodate functions
    )

    # The environment will automatically await async uptodate functions
    template = await env.get_template_async("example.html")
    result = await template.render_async()
    print(result)


asyncio.run(main())

Key Features:

• Both sync and async uptodate functions are supported
• Async uptodate functions are automatically awaited during template caching
• No code changes needed - existing sync uptodate functions continue to work
• Useful for remote template sources (databases, APIs, remote filesystems)

License

BSD-3-Clause