In what cases and systems are context processors used?

Context processors in Python are often used in web frameworks, for example, in Django. They allow automatically adding certain variables or data to the template context so that this data is accessible in all or specific templates without the need to explicitly pass them from each view.

When to use:

• When certain data (e.g., current user data, site settings, navigation menu) needs to be available in all templates.
• To simplify passing repetitive data to templates.
• In templating systems where the template context is dynamically generated.

Example: In Django, you can create a context processor that adds the current year to the context:

# myapp/context_processors.py
from datetime import datetime

def current_year(request):
    return {'current_year': datetime.now().year}

And include it in your settings:

TEMPLATES = [
    {
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                # ... other processors ...
                'myapp.context_processors.current_year',
            ],
        },
    },
]

Now, in any template, you can use the variable {{ current_year }} without additional passing from the view.