Prompt templates

To facilitate prompting management we use Jinja2 templating engine. Jinja2 is quite powerful because it has a rich language for loops, controls and variable rendering with proper environment management, therefore there is no need to reinvent the wheel.

See also

Unlike other LLM orchestration and chaining APIs, Feste prompts are language-aware. This is a design choice to enable multilingual prompts and proper language management. We adopted the ISO-639 for it.

Note

All examples in this page are executed in eager mode for clarity.

Simple example

The most simple use of a prompt template is the following:

from feste.prompt import Prompt

p = Prompt("Hello {{message}}!")
res = p(message="world")

print(res)
"Hello world!"

Language-aware prompt

The default language of a prompt is English (en), but you can change that:

p = Prompt("Olá {{mensagem}}!", language="pt")

print(p.language)
Language(part3='por', part1='pt', name='Portuguese', ...)

By using the correct language in the prompt, you will get warnings if you do things like concatenation of prompts with different languages:

p_en = Prompt("Hello {{message}}!")
p_pt = Prompt("Olá prompt", language="pt")

p_new = p_en + p_pt

"LanguageMismatch: You are concatenating prompts with different languages."

Getting template variables

You can also get the list of prompt variables from your template:

p = Prompt("Hello {{message}}! My name is {{name}}.")

print(p.variables())
{'message', 'name'}

Prompt environment

Sometimes it is helpful to share a common environment across different prompt templates. Think of systems where for example you want to share an agent name across different templates. To achieve that you can use an environment like in the example below:

from feste.prompt import Prompt, FesteEnvironment

smart_bot_env = FesteEnvironment()
smart_bot_env.globals.update({
    "agent_name": "SmartBot"
})
p = Prompt("Hello {{message}}! My name is {{agent_name}}.",
           environment=smart_bot_env)

print(p(message="John"))
"Hello John! My name is SmartBot."