# Rendering Contexts

URL: /docs/usage/rendering-contexts/
Section: usage
Tags: usage, contexts

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Rendering Contexts Pass data to templates through the rendering context. Basic Rendering Pass variables as keyword arguments: template = env.get_template("page.html") html = template.render( title="My Page", user=current_user, items=item_list, ) Or as a dictionary: context = { "title": "My Page", "user": current_user, "items": item_list, } html = template.render(context) Convenience Methods Environment provides shortcuts: # Combines get_template() + render() html = env.render("page.html", title="Hello") # Combines from_string() + render() html = env.render_string("{{ x * 2 }}", x=21) Global Variables Variables available in all templates: env = Environment(loader=FileSystemLoader("templates/")) # Add globals env.add_global("site_name", "My Site") env.add_global("current_year", 2024) env.add_global("format_date", format_date_func) Access in templates: <title>{{ site_name }}</title> <footer>© {{ current_year }}</footer> {{ format_date(post.date) }} Built-in Globals Kida includes common Python builtins: {{ range(10) }} {{ len(items) }} {{ dict(a=1, b=2) }} {{ max(scores) }} Available: range, dict, list, set, tuple, len, str, int, float, bool, abs, min, max, sum, sorted, reversed, enumerate, zip, map, filter. Object Access Templates access object attributes: class User: def __init__(self, name, email): self.name = name self.email = email template.render(user=User("Alice", "alice@example.com")) {{ user.name }} {{ user.email }} Dictionary Access template.render(config={"timeout": 30, "retries": 3}) {{ config.timeout }} {{ config["timeout"] }} Nested Contexts Build complex nested data: template.render( site={ "title": "My Site", "nav": [ {"title": "Home", "url": "/"}, {"title": "About", "url": "/about"}, ], }, page={ "title": "Welcome", "content": "Hello, world!", }, ) <title>{{ page.title }} - {{ site.title }}</title> <nav> {% for item in site.nav %} <a href="{{ item.url }}">{{ item.title }}</a> {% end %} </nav> Undefined Variables By default, undefined variables raise errors: template = env.from_string("{{ missing }}") template.render() # Raises UndefinedError Use default filter for optional values: {{ user.nickname | default("Anonymous") }} {{ config.timeout | default(30) }} Context Isolation Each render() call starts with a fresh context: # These don't affect each other html1 = template.render(x=1) html2 = template.render(x=2) Globals are shared but render context is isolated. Best Practices Keep Context Flat # ✅ Flat, easy to access template.render( title=page.title, user=current_user, items=items, ) # ❌ Deeply nested template.render( data={ "page": {"meta": {"title": ...}}, ... } ) Use Typed Objects # ✅ IDE support, validation @dataclass class PageContext: title: str user: User items: list[Item] template.render(**asdict(PageContext(...))) Precompute in Python # ✅ Python handles complexity template.render( formatted_items=[format_item(i) for i in items], total=sum(i.price for i in items), ) # ❌ Complex logic in template # {% set total = 0 %} # {% for item in items %}{% set total = total + item.price %}{% end %} See Also Escaping — HTML escaping Custom Globals — Add global functions API Reference — Environment.render()

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