typantic 0.4.0

Auto-generate Typer CLI interfaces from Pydantic models.

typantic

Auto-generate Typer CLI interfaces from Pydantic models.

Define your config once as a Pydantic model with validators, and get a fully-typed CLI for free — no duplication, no drift.

Installation

pip install typantic

Quick start

from pathlib import Path
from typing import Annotated

import typer
from pydantic import AfterValidator, BaseModel, Field

from typantic import pydantic_to_typer


# 1. Define your config with validators
class Config(BaseModel):
    images: Annotated[
        list[Path],
        Field(description="Image folders to process.", kw_only=False),
    ]
    output: Annotated[
        Path,
        AfterValidator(Path.resolve),
        Field(description="Output directory.", kw_only=True),
    ]
    threshold: Annotated[
        float,
        Field(default=0.5, description="Detection threshold.", kw_only=True),
    ]
    seed: Annotated[
        int | None,
        Field(default=None, description="Random seed.", kw_only=True),
    ]


# 2. Use the decorator — that's it
app = typer.Typer()

@app.command()
@pydantic_to_typer(Config)
def run(config: Config):
    """Process images with validation."""
    print(config)

if __name__ == "__main__":
    app()

$ python example.py --help

 Usage: example.py [OPTIONS] IMAGES...

 Process images with validation.

╭─ Arguments ──────────────────────────────────────────────────╮
│ *  images  IMAGES...  Image folders to process.  [required]  │
╰──────────────────────────────────────────────────────────────╯
╭─ Options ────────────────────────────────────────────────────╮
│ *  --output     PATH     Output directory.  [required]       │
│    --threshold  FLOAT    Detection threshold.  [default: 0.5]│
│    --seed       INTEGER  Random seed.  [default: (None)]     │
│    --help                Show this message and exit.         │
╰──────────────────────────────────────────────────────────────╯

How it works

The @pydantic_to_typer(Model) decorator:

1. Reads Model.model_fields to discover field names, types, descriptions, and defaults
2. Strips Annotated validator metadata to extract the base types Typer understands
3. Maps kw_only=False → typer.Argument, kw_only=True → typer.Option
4. Flattens nested BaseModel fields into prefixed parameters
5. Rewrites the function's __signature__ so Typer sees the expanded parameters
6. At call time, re-nests the raw CLI values and passes them into Model(...) so all Pydantic validators run

Your function receives the validated model instance — validators, default_factory, union types, and everything else works exactly as in Pydantic.

Features

Pydantic	CLI result
kw_only=False	typer.Argument (positional)
kw_only=True or unset	typer.Option (--flag)
Field(description=...)	help=... in the CLI
Field(default=...)	Default value shown in --help
Field(default_factory=...)	Re-evaluated on every invocation
Field(ge=..., le=...)	Typer min / max (validated + shown)
Literal["a", "b"]	CLI choices
Enum, tuple[...]	Choices / multi-value option
nested BaseModel	Flattened into --prefix-field options
SecretStr, SecretBytes	Hidden input (secure prompt if required)
int | None	Optional CLI option
default=None	Rendered as [default: (None)]
list[Path]	Variadic positional argument
AfterValidator, BeforeValidator	Run at call time via Pydantic

Validators that raise ValueError / AssertionError surface as Typer parameter errors; other exception types propagate unchanged.

Per-field CLI hints

Customise individual flags with Field(json_schema_extra=...):

class Config(BaseModel):
    verbose: Annotated[
        bool,
        Field(default=False, json_schema_extra={"cli_short": "-v"}),
    ]
    output: Annotated[
        Path,
        Field(description="Output path.", json_schema_extra={"cli_name": "--dest"}),
    ]
    api_key: Annotated[
        str,
        Field(default="", json_schema_extra={"cli_envvar": "MYAPP_API_KEY"}),
    ]

Key	Effect
cli_short	Adds a short flag (e.g. -v) alongside the long one
cli_name	Replaces the derived long flag (e.g. --dest)
cli_envvar	Reads the value from an environment variable

Nested models

Fields whose type is itself a BaseModel are flattened into prefixed options, so layered configs map onto the CLI without manual wiring:

class Database(BaseModel):
    host: Annotated[str, Field(default="localhost", description="DB host.")]
    port: Annotated[int, Field(default=5432, ge=1, le=65535, description="DB port.")]


class Config(BaseModel):
    name: Annotated[str, Field(description="App name.", kw_only=False)]
    db: Database  # -> --db-host, --db-port

$ python example.py myapp --db-host db.internal --db-port 9000

The values are re-nested before the model is constructed, so Database's own validators and defaults apply as usual.

Registering commands without a stub

add_command wires a model and a handler onto a Typer app directly, skipping the decorate-a-stub-function boilerplate:

import typer

from typantic import add_command

app = typer.Typer()


def run(config: Config) -> None:
    print(config)


add_command(app, Config, run)            # command name defaults to "run"
add_command(app, Config, run, name="go")  # or set it explicitly

Help panels for mixin-composed models

Large configs composed from mixins can group their options into titled Rich help panels. Opt in with subpanels=True and give each mixin a cli_panel class attribute — every option lands in the panel of the class that defines its field:

from typing import Annotated, ClassVar

from pydantic import BaseModel, Field

from typantic import pydantic_to_typer


class ComputeMixin(BaseModel):
    cli_panel: ClassVar[str] = "Compute"

    cpus: Annotated[int, Field(default=4, description="CPU count.")]


class Config(ComputeMixin):
    dry_run: Annotated[bool, Field(default=False, description="Dry run.")]


@app.command()
@pydantic_to_typer(Config, subpanels=True)
def run(config: Config): ...

$ python example.py --help

 Usage: example.py [OPTIONS]

╭─ Options ──────────────────────────────────────────────────────╮
│ --dry-run    --no-dry-run    Dry run.  [default: no-dry-run]   │
│ --help                       Show this message and exit.       │
╰────────────────────────────────────────────────────────────────╯
╭─ Compute ──────────────────────────────────────────────────────╮
│ --cpus        INTEGER        CPU count.  [default: 4]          │
╰────────────────────────────────────────────────────────────────╯

--cpus renders under a "Compute" panel; --dry-run stays in the default options group (its defining class declares no cli_panel). Arguments are never panelled.

Config files

Some configs are too large or too nested to pass as flags every time. Opt in with config_file=True and the command can be driven by a YAML/JSON file as well. Two options are injected:

• --generate-config PATH — write an editable default template, then exit without running;
• --config PATH — load settings from a file as the base; any flags you also pass override the file.

from typing import Annotated

import typer
from pydantic import BaseModel, Field

from typantic import add_command


class Database(BaseModel):
    host: Annotated[str, Field(description="DB host.")]      # required
    port: Annotated[int, Field(default=5432, description="DB port.")]


class Config(BaseModel):
    name: Annotated[str, Field(description="App name.")]      # required
    db: Database                                             # required nested model
    workers: Annotated[int, Field(default=4, description="Worker count.")]
    tags: set[str] = {"default"}


app = typer.Typer()


def run(config: Config) -> None:
    print(config)


add_command(app, Config, run, name="run", config_file=True)

Generate a template — required fields become <REQUIRED: ...> placeholders, and nested models are expanded so their shape is visible:

$ myapp run --generate-config run.yaml
$ cat run.yaml
name: '<REQUIRED: App name.>'
db:
  host: '<REQUIRED: DB host.>'
  port: 5432
workers: 4
tags:
- default

Fill in the required values and run from the file (or override individual settings with flags, which take precedence over the file):

$ cat run.yaml
name: my-service
db:
  host: db.internal
  port: 9000
workers: 8
tags: [eu, prod]

$ myapp run --config run.yaml                 # run entirely from the file
$ myapp run --config run.yaml --workers 16    # file as base, --workers overrides

--help lists both options under a Config file panel:

╭─ Config file ──────────────────────────────────────────────────╮
│ --config           PATH  Load settings from a YAML/JSON file    │
│                          (flags passed still override).         │
│ --generate-config  PATH  Write a default config template to     │
│                          PATH and exit.                         │
╰────────────────────────────────────────────────────────────────╯

Because --config may supply them, required fields are made optional at the Typer layer; Pydantic re-checks requiredness after merging file and flags, so a value missing from both is still reported as an error — it just no longer renders as [required] in --help. A --config document must be a mapping; a bad suffix, unparseable content, or a non-mapping top level raises a ValueError.

Requirements

• Python ≥ 3.12 (tested on 3.12–3.15)
• Pydantic ≥ 2.10
• Typer ≥ 0.26
• PyYAML ≥ 6.0

License

MIT