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Most backends operate on text. For these backends/models, Mellea has an opinionated stance on how to transform Python objects into text: the TemplateFormatter. In most cases, you will want to create templates when adding a new component to the standard library or when customizing an existing component for a new model.

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Templates

Mellea’s TemplateFormatter uses jinja2 templates to format objects when passing them to models for generation. These templates can be stored directly in the class/object, or, more typically, the templates are stored in a directory, with each object having a specific file. For examples of the templates, see mellea/templates/prompts/default. See the customization section below for a description of how the formatter chooses which template to use.

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Template Representations

Along with a template, each class/object needs to define the arguments that will be supplied when rendering the template. This happens in the component’s format_for_llm() function. It returns either a string or a TemplateRepresentation. string: the simplest approach is for this method to return a string representation of the object. This avoids templating altogether. TemplateRepresentation: It can also return a TemplateRepresentation object. This representation contains: - a reference to the component - a dictionary of arguments that will be passed to the template renderer - a list of tools/functions that relate to the component It also contains either of the following fields
  • template: a string representation of a jinja2 template that can be rendered with the provided args
  • template_order: a list of strings describing the name of the template file to look up (without the “.jinja2” suffix); * denotes the class name.

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Customization

By writing a new template and/or changing the TemplateRepresentation of a component you can customize the textual representation. You can also customize based on the model.

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Choosing a Template

Assuming a component’s TemplateRepresentation contains a template_order field, the default TemplateFormatter grabs the relevant template by looking at the following places in order for each template in the template_order:
  1. the formatter’s cached templates if the template has been looked up recently
  2. the formatter’s specified template path
  3. the package that the object getting formatted is from (either ‘mellea’ or some third party package)
If the default formatter searches the template path or the package, it uses the following logic:
  • look in the .../templates/prompts/... directory
  • traverse sub-directories in that path that match the formatter’s model id (ie ibm-granite/granite-3.2-8b-instruct will match .../templates/prompts/granite/granite-3-2/instruct) or default (ie .../templates/prompts/default)
  • return the template at the deepest directory path
  • the default template formatter assumes that a model will only have one match in any given directory; in other words, traversing a templates directory with both prompts/granite/... and prompts/ibm/... for ibm-granite/granite-3.2-8b-instruct should not happen

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Editing an Existing Class

To customize the template and template representation of an existing class, simply create a new class that inherits from the class you want to edit. Then, override the format_for_llm function and create a new template. See mellea/docs/examples/mify/rich_document_advanced.py