contexting 0.1.1

Template-based prompt assembly with ordered slot injectors

contexting

Template-based prompt assembly. Fill {{slot}} placeholders in a base prompt using ordered injectors and a runtime context.

Installation

pip install contexting

How it works

• Inline injection — if a slot exists in the template, the injector's output replaces it directly
• Appended injection — if the slot is absent, the output is collected and appended after the filled template, separated by a blank line
• Base fill — after all injectors run, remaining {{slots}} are filled directly from context (strings and numbers only)

API

from contexting import assemble, create_injector

create_injector(slot, fn)

param	type	description
slot	str	name matching {{slot}} in the template
fn	Callable[[dict], str]	receives the full context, returns the string to inject

assemble(base_prompt, rules, context)

param	type	description
base_prompt	str	template string with {{slot}} placeholders
rules	list[Injector]	ordered injectors applied before base fill
context	dict	passed to every injector fn; also fills remaining slots

Returns the assembled str.

Examples

Inline and appended injection

from contexting import assemble, create_injector

base_prompt = 'You are a {{role}} assistant for the language {{lang}}.'

# Inline — {{role}} exists in template, replaced directly
role_injector = create_injector('role', lambda ctx:
    'senior software engineer' if ctx.get('senior') else 'helpful coding'
)

# Appended — {{constraints}} absent, output appended after a blank line
constraints_injector = create_injector('constraints', lambda ctx:
    'Never suggest running untrusted code. Always explain risks.' if ctx.get('safe') else ''
)

lang_injector = create_injector('lang', lambda ctx:
    'javascript, node and typescript' if ctx.get('lang') == 'javascript' else 'python and java'
)

prompt = assemble(base_prompt, [role_injector, constraints_injector, lang_injector], {
    'senior': True,
    'safe': True,
    'lang': 'javascript',
})

print(prompt)
# You are a senior software engineer assistant for the language javascript, node and typescript.
#
# Never suggest running untrusted code. Always explain risks.

Base fill from context

Remaining slots not handled by any injector are filled directly from context:

prompt = assemble('Hello {{name}}, you are using {{lang}}.', [], {
    'name': 'Alice',
    'lang': 'python',
})

print(prompt)
# Hello Alice, you are using python.

Language-aware prompts

base_prompt = '{{lang_style}} Help the user with their question about {{topic}}.'

lang_style = create_injector('lang_style', lambda ctx: {
    'es': 'Respond only in Spanish. Be warm and conversational.',
    'fr': 'Respond only in French. Be formal and precise.',
}.get(ctx.get('lang'), 'Respond in English. Be clear and concise.'))

prompt = assemble(base_prompt, [lang_style], {'lang': 'es', 'topic': 'cooking'})

print(prompt)
# Respond only in Spanish. Be warm and conversational. Help the user with their question about cooking.