Prompt Template Systems
Template Architecture
Basic Template Structure
class PromptTemplate:
def __init__(self, template_string, variables=None):
self.template = template_string
self.variables = variables or []
def render(self, **kwargs):
missing = set(self.variables) - set(kwargs.keys())
if missing:
raise ValueError(f"Missing required variables: {missing}")
return self.template.format(**kwargs)
# Usage
template = PromptTemplate(
template_string="Translate {text} from {source_lang} to {target_lang}",
variables=['text', 'source_lang', 'target_lang']
)
prompt = template.render(
text="Hello world",
source_lang="English",
target_lang="Spanish"
)
Conditional Templates
class ConditionalTemplate(PromptTemplate):
def render(self, **kwargs):
# Process conditional blocks
result = self.template
# Handle if-blocks: {{#if variable}}content{{/if}}
import re
if_pattern = r'\{\{#if (\w+)\}\}(.*?)\{\{/if\}\}'
def replace_if(match):
var_name = match.group(1)
content = match.group(2)
return content if kwargs.get(var_name) else ''
result = re.sub(if_pattern, replace_if, result, flags=re.DOTALL)
# Handle for-loops: {{#each items}}{{this}}{{/each}}
each_pattern = r'\{\{#each (\w+)\}\}(.*?)\{\{/each\}\}'
def replace_each(match):
var_name = match.group(1)
content = match.group(2)
items = kwargs.get(var_name, [])
return '\\n'.join(content.replace('{{this}}', str(item)) for item in items)
result = re.sub(each_pattern, replace_each, result, flags=re.DOTALL)
# Finally, render remaining variables
return result.format(**kwargs)
# Usage
template = ConditionalTemplate("""
Analyze the following text:
{text}
{{#if include_sentiment}}
Provide sentiment analysis.
{{/if}}
{{#if include_entities}}
Extract named entities.
{{/if}}
{{#if examples}}
Reference examples:
{{#each examples}}
- {{this}}
{{/each}}
{{/if}}
""")
Modular Template Composition
class ModularTemplate:
def __init__(self):
self.components = {}
def register_component(self, name, template):
self.components[name] = template
def render(self, structure, **kwargs):
parts = []
for component_name in structure:
if component_name in self.components:
component = self.components[component_name]
parts.append(component.format(**kwargs))
return '\\n\\n'.join(parts)
# Usage
builder = ModularTemplate()
builder.register_component('system', "You are a {role}.")
builder.register_component('context', "Context: {context}")
builder.register_component('instruction', "Task: {task}")
builder.register_component('examples', "Examples:\\n{examples}")
builder.register_component('input', "Input: {input}")
builder.register_component('format', "Output format: {format}")
# Compose different templates for different scenarios
basic_prompt = builder.render(
['system', 'instruction', 'input'],
role='helpful assistant',
instruction='Summarize the text',
input='...'
)
advanced_prompt = builder.render(
['system', 'context', 'examples', 'instruction', 'input', 'format'],
role='expert analyst',
context='Financial analysis',
examples='...',
instruction='Analyze sentiment',
input='...',
format='JSON'
)
Common Template Patterns
Classification Template
CLASSIFICATION_TEMPLATE = """
Classify the following {content_type} into one of these categories: {categories}
{{#if description}}
Category descriptions:
{description}
{{/if}}
{{#if examples}}
Examples:
{examples}
{{/if}}
{content_type}: {input}
Category:"""
Extraction Template
EXTRACTION_TEMPLATE = """
Extract structured information from the {content_type}.
Required fields:
{field_definitions}
{{#if examples}}
Example extraction:
{examples}
{{/if}}
{content_type}: {input}
Extracted information (JSON):"""
Generation Template
GENERATION_TEMPLATE = """
Generate {output_type} based on the following {input_type}.
Requirements:
{requirements}
{{#if style}}
Style: {style}
{{/if}}
{{#if constraints}}
Constraints:
{constraints}
{{/if}}
{{#if examples}}
Examples:
{examples}
{{/if}}
{input_type}: {input}
{output_type}:"""
Transformation Template
TRANSFORMATION_TEMPLATE = """
Transform the input {source_format} to {target_format}.
Transformation rules:
{rules}
{{#if examples}}
Example transformations:
{examples}
{{/if}}
Input {source_format}:
{input}
Output {target_format}:"""
Advanced Features
Template Inheritance
class TemplateRegistry:
def __init__(self):
self.templates = {}
def register(self, name, template, parent=None):
if parent and parent in self.templates:
# Inherit from parent
base = self.templates[parent]
template = self.merge_templates(base, template)
self.templates[name] = template
def merge_templates(self, parent, child):
# Child overwrites parent sections
return {**parent, **child}
# Usage
registry = TemplateRegistry()
registry.register('base_analysis', {
'system': 'You are an expert analyst.',
'format': 'Provide analysis in structured format.'
})
registry.register('sentiment_analysis', {
'instruction': 'Analyze sentiment',
'format': 'Provide sentiment score from -1 to 1.'
}, parent='base_analysis')
Variable Validation
class ValidatedTemplate:
def __init__(self, template, schema):
self.template = template
self.schema = schema
def validate_vars(self, **kwargs):
for var_name, var_schema in self.schema.items():
if var_name in kwargs:
value = kwargs[var_name]
# Type validation
if 'type' in var_schema:
expected_type = var_schema['type']
if not isinstance(value, expected_type):
raise TypeError(f"{var_name} must be {expected_type}")
# Range validation
if 'min' in var_schema and value < var_schema['min']:
raise ValueError(f"{var_name} must be >= {var_schema['min']}")
if 'max' in var_schema and value > var_schema['max']:
raise ValueError(f"{var_name} must be <= {var_schema['max']}")
# Enum validation
if 'choices' in var_schema and value not in var_schema['choices']:
raise ValueError(f"{var_name} must be one of {var_schema['choices']}")
def render(self, **kwargs):
self.validate_vars(**kwargs)
return self.template.format(**kwargs)
# Usage
template = ValidatedTemplate(
template="Summarize in {length} words with {tone} tone",
schema={
'length': {'type': int, 'min': 10, 'max': 500},
'tone': {'type': str, 'choices': ['formal', 'casual', 'technical']}
}
)
Template Caching
class CachedTemplate:
def __init__(self, template):
self.template = template
self.cache = {}
def render(self, use_cache=True, **kwargs):
if use_cache:
cache_key = self.get_cache_key(kwargs)
if cache_key in self.cache:
return self.cache[cache_key]
result = self.template.format(**kwargs)
if use_cache:
self.cache[cache_key] = result
return result
def get_cache_key(self, kwargs):
return hash(frozenset(kwargs.items()))
def clear_cache(self):
self.cache = {}
Multi-Turn Templates
Conversation Template
class ConversationTemplate:
def __init__(self, system_prompt):
self.system_prompt = system_prompt
self.history = []
def add_user_message(self, message):
self.history.append({'role': 'user', 'content': message})
def add_assistant_message(self, message):
self.history.append({'role': 'assistant', 'content': message})
def render_for_api(self):
messages = [{'role': 'system', 'content': self.system_prompt}]
messages.extend(self.history)
return messages
def render_as_text(self):
result = f"System: {self.system_prompt}\\n\\n"
for msg in self.history:
role = msg['role'].capitalize()
result += f"{role}: {msg['content']}\\n\\n"
return result
State-Based Templates
class StatefulTemplate:
def __init__(self):
self.state = {}
self.templates = {}
def set_state(self, **kwargs):
self.state.update(kwargs)
def register_state_template(self, state_name, template):
self.templates[state_name] = template
def render(self):
current_state = self.state.get('current_state', 'default')
template = self.templates.get(current_state)
if not template:
raise ValueError(f"No template for state: {current_state}")
return template.format(**self.state)
# Usage for multi-step workflows
workflow = StatefulTemplate()
workflow.register_state_template('init', """
Welcome! Let's {task}.
What is your {first_input}?
""")
workflow.register_state_template('processing', """
Thanks! Processing {first_input}.
Now, what is your {second_input}?
""")
workflow.register_state_template('complete', """
Great! Based on:
- {first_input}
- {second_input}
Here's the result: {result}
""")
Best Practices
- Keep It DRY: Use templates to avoid repetition
- Validate Early: Check variables before rendering
- Version Templates: Track changes like code
- Test Variations: Ensure templates work with diverse inputs
- Document Variables: Clearly specify required/optional variables
- Use Type Hints: Make variable types explicit
- Provide Defaults: Set sensible default values where appropriate
- Cache Wisely: Cache static templates, not dynamic ones
Template Libraries
Question Answering
QA_TEMPLATES = {
'factual': """Answer the question based on the context.
Context: {context}
Question: {question}
Answer:""",
'multi_hop': """Answer the question by reasoning across multiple facts.
Facts: {facts}
Question: {question}
Reasoning:""",
'conversational': """Continue the conversation naturally.
Previous conversation:
{history}
User: {question}
Assistant:"""
}
Content Generation
GENERATION_TEMPLATES = {
'blog_post': """Write a blog post about {topic}.
Requirements:
- Length: {word_count} words
- Tone: {tone}
- Include: {key_points}
Blog post:""",
'product_description': """Write a product description for {product}.
Features: {features}
Benefits: {benefits}
Target audience: {audience}
Description:""",
'email': """Write a {type} email.
To: {recipient}
Context: {context}
Key points: {key_points}
Email:"""
}
Performance Considerations
- Pre-compile templates for repeated use
- Cache rendered templates when variables are static
- Minimize string concatenation in loops
- Use efficient string formatting (f-strings, .format())
- Profile template rendering for bottlenecks
