prompt-assemble 0.1.6

A lightweight prompt assembly library using sigil-based substitution with no template logic

prompt-assemble

A lightweight prompt assembly library for building dynamic prompts with sigil-based substitution. No logic in templates — templates stay dumb, logic stays in Python.

Features

• Sigil-based substitution — Simple placeholder syntax ([[VAR_NAME]] and [[PROMPT: name]])
• Format-agnostic — Works with loose XML, JSON, or plain text
• Recursive substitution — Variable values can contain sigils, resolved in a second pass
• Comments support — Single-line (#!) and multiline (<!-- -->) comments
• No template logic — Loops, conditionals, and transforms belong in Python
• Portable — Easy to use across different environments

Installation

pip install prompt-assemble

Quick Start

from prompt_assemble import assemble

template = """
<system>
You are a [[PROMPT: persona]] specializing in [[DOMAIN]].
</system>

<task>
[[PROMPT: task-instructions]]
</task>

<question>
[[QUESTION]]
</question>
"""

components = {
    "persona": "expert software architect",
    "task-instructions": "Analyze the code and provide recommendations.",
}

variables = {
    "DOMAIN": "Python development",
    "QUESTION": "How can we improve this function?",
}

result = assemble(template, components=components, variables=variables)
print(result)

Format Support

Loose XML

<system>You are a [[PROMPT: persona]]</system>
<task>[[PROMPT: task-instructions]]</task>

JSON

{
  "system": "You are a [[PROMPT: persona]]",
  "task": "[[PROMPT: task-instructions]]"
}

Plain Text

Subject: [[SUBJECT]]

Body:
[[BODY]]

Sigil Syntax

Sigil	Purpose
[[VAR_NAME]]	Simple variable substitution
[[PROMPT: name]]	Inject a named prompt component
[[PROMPT_TAG: tag1, tag2]]	Inject all prompts matching tags (AND intersection)
[[PROMPT_TAG:N: tag1, tag2]]	Inject N most recent prompts matching tags

Comments

#! Single line comment

<!-- Multi-line
     comment -->

Comments are stripped before substitution and never reach the model.

Recursive Substitution

Variable values can themselves contain sigils:

variables = {
    "TASK": "Analyze [[CODE_TYPE]] code",
    "CODE_TYPE": "Python",
}

# Second pass resolves nested sigils

CLI Usage

pambl --template prompt.prompt --components components.json --variables vars.json

Database

PostgreSQL is required. The DatabaseSource implementation uses PostgreSQL-specific features including automatic reconnection on timeout and transaction management optimized for reliability.

PostgreSQL Support

• PostgreSQL 10+ (required for production and testing)
• Automatic connection reconnection on timeout
• Multi-tenant support via table prefixes
• Version history and tagging

Quick Setup with PostgreSQL

import psycopg2
from prompt_assemble.sources import DatabaseSource

# Connect to PostgreSQL
conn = psycopg2.connect(
    host="localhost",
    database="prompts",
    user="postgres",
    password="secret"
)

# Create source with table prefix for multi-tenant support
source = DatabaseSource(conn, table_prefix="prod_")

# Use with PromptProvider
from prompt_assemble import PromptProvider

provider = PromptProvider(source)

Docker Compose with PostgreSQL

See DOCKER.md for a complete Docker Compose setup with PostgreSQL.

Environment Variables

The prompt-assemble library and UI support the following environment variables for configuration:

Starting the UI Server

Use the provided startup script:

python start_ui_db.py

This script automatically:

• Connects to PostgreSQL using environment variables
• Initializes the database schema
• Starts the Flask UI server
• Creates tables with the configured prefix

Database Configuration (PostgreSQL)

Variable	Type	Default	Description
DB_HOSTNAME	string	localhost	PostgreSQL server hostname
DB_PORT	int	5432	PostgreSQL server port
DB_USERNAME	string	postgres	PostgreSQL username
DB_PASSWORD	string	(required)	PostgreSQL password
DB_DATABASE	string	prompts	PostgreSQL database name
DB_SSLMODE	string	require	SSL mode: require, prefer, disable
DB_PREFIX	string	pambl_	Table name prefix (e.g., tables become pambl_prompts, pambl_prompt_tags)
PORT	int	8000	Port for the Flask UI server

Example - Local PostgreSQL:

export DB_HOSTNAME=localhost
export DB_PORT=5432
export DB_USERNAME=postgres
export DB_PASSWORD=your_password
export DB_DATABASE=prompts
export DB_PREFIX=pambl_
export PORT=8000

python start_ui_db.py

Example - DigitalOcean Managed PostgreSQL:

export DB_HOSTNAME=db-postgresql-sfo2-xxxx-do-user-xxxxx-0.e.db.ondigitalocean.com
export DB_PORT=25060
export DB_USERNAME=pambl_user
export DB_PASSWORD=your_secure_password
export DB_DATABASE=pambl_db
export DB_SSLMODE=require
export DB_PREFIX=pambl_
export PORT=8000

python start_ui_db.py

Programmatic Configuration (Legacy)

Variable	Type	Default	Description
PROMPT_ASSEMBLE_UI	bool	false	Enable/disable the web UI server. Set to "true" to activate
PROMPT_ASSEMBLE_TABLE_PREFIX	string	"" (empty)	Table prefix (deprecated - use DB_PREFIX instead)

Listener & Event Configuration

Variable	Type	Default	Description
None currently	-	-	Listener callbacks are configured programmatically

Configuration Examples

Development Environment (Local PostgreSQL)

export DB_HOSTNAME=localhost
export DB_PORT=5432
export DB_USERNAME=postgres
export DB_PASSWORD=dev_password
export DB_DATABASE=prompts_dev
export DB_SSLMODE=disable
export DB_PREFIX=dev_
export PORT=8000

python start_ui_db.py

Production (DigitalOcean PostgreSQL)

export DB_HOSTNAME=db-postgresql-sfo2-xxxxx-do-user-xxxxx-0.e.db.ondigitalocean.com
export DB_PORT=25060
export DB_USERNAME=prod_user
export DB_PASSWORD=your_secure_password
export DB_DATABASE=prompts_prod
export DB_SSLMODE=require
export DB_PREFIX=prod_
export PORT=8000

python start_ui_db.py

Testing

export DB_HOSTNAME=localhost
export DB_PORT=5432
export DB_USERNAME=postgres
export DB_PASSWORD=test_password
export DB_DATABASE=prompts_test
export DB_PREFIX=test_
export PORT=8001

python start_ui_db.py

Programmatic Configuration

You can also configure these settings directly in Python:

from prompt_assemble.sources import DatabaseSource
from prompt_assemble.api import run_server
import psycopg2

# Configure PostgreSQL database with table prefix
conn = psycopg2.connect(
    host="localhost",
    database="prompts",
    user="postgres",
    password="secret"
)
source = DatabaseSource(conn, table_prefix='myapp_')

# Configure Flask server
run_server(
    source=source,
    host='0.0.0.0',
    port=8000,
    debug=False
)

Quick Reference

All Environment Variables

# UI Server (Required for web interface)
PROMPT_ASSEMBLE_UI=true

# Flask Configuration (Optional)
FLASK_HOST=0.0.0.0
FLASK_PORT=8000
FLASK_DEBUG=false

# PostgreSQL Database Connection
DB_HOSTNAME=localhost
DB_PORT=5432
DB_USERNAME=postgres
DB_PASSWORD=secret
DB_DATABASE=prompts

# Database Options
PROMPT_ASSEMBLE_TABLE_PREFIX=myapp_  # Table prefix for multi-tenancy

Database Driver

Install psycopg2 for PostgreSQL:

pip install psycopg2-binary

Connection Resilience

The DatabaseSource automatically handles connection timeouts and network interruptions:

• Automatic reconnection — Detects closed connections and reconnects transparently
• Health checks — Validates connection before each operation
• Timeout recovery — Handles PostgreSQL idle timeout gracefully

No configuration required — reconnection happens automatically on these operations:

• save_prompt() - Save/update prompts
• delete_prompt() - Delete prompts
• refresh() - Reload metadata
• get_raw() - Fetch content
• All variable set operations

Testing

Run the full test suite:

pytest tests/

Note: Database-specific tests require PostgreSQL:

# Skip database tests (for environments without PostgreSQL)
pytest tests/ -k "not test_database"

# Run only with PostgreSQL available
PGHOST=localhost PGUSER=postgres PGPASSWORD=secret PGDATABASE=test_prompts pytest tests/test_database_source.py

Test Coverage: 118 passing tests covering core library, FileSystem source, and listener system. PostgreSQL-specific tests are marked as requiring PostgreSQL.

Contributing

Contributions welcome! Please open an issue or submit a pull request.

License

MIT License — see LICENSE file for details.