Using Python 3.14 template strings to write Python

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2025-07-03

Python 3.14 template strings look pretty groovy right?

Let's use a new library of mine - trolskgen - that utilises them for maximum cuteness.

Note that it is still possible to use this library with Python < 3.14 - see the docs.

Imagine you have some weird schema definition from somewhere, for example:

<A x="str" y="int"> <B many="true" z="int" /> <C x="str" /> </A>

And you want to codegen the Python:

from __future__ import annotations import pydantic class A(pydantic.BaseModel): x: str y: int b: list[B] c: C class B(pydantic.BaseModel): z: int class C(pydantic.BaseModel): x: str

Well, let's go and do it - with template strings!

Firstly:

pip install trolskgen

Then:

import io from string.templatelib import Template import xml.etree.ElementTree as ET import trolskgen schema = """ <A x="str" y="int"> <B many="true" z="int" /> <C x="str" /> </A> """ schema_xml = ET.parse(io.StringIO(schema)).getroot() def as_field(node: ET.Element) -> Template: t = trolskgen.t(node.tag) if node.attrib.get("many") == "true": t = list[t] return t"{node.tag.lower()}: {t}" def yield_classes(node: ET.Element) -> Template: fields = [t"{k}: {trolskgen.t(v)}" for k, v in node.attrib.items() if k != "many"] fields += [as_field(c) for c in node] yield t""" class {node.tag}(pydantic.BaseModel): {fields:*} """ for c in node: yield from yield_classes(c) source_template = t""" from __future__ import annotations import pydantic {list(yield_classes(schema_xml)):*} """ print(trolskgen.to_source(source_template))

Neat huh?

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To immedi-run the above, download code then: uv run trolskgen_example.py