clattr

Easily make a command line interface from any interface in your code. How easily? This easy:

import clattr

def my_program(a: int, b: str = "not provided"):
  print(f"Running some code with: a={a}, b={b}")

if __name__ == "__main__":
  clattr.call(my_program)

That's all it takes. Clattr will inspect your function and collect the values it needs it from command line arguments, environment variables, or config files, and then call it.

python examples/function --a 1

Running some code with: a=1, b=not provided

If you want to think in a more data oriented design, you can have clattr construct a data object for you and use it as you please.

import attr
import clattr


@attr.s(auto_attribs=True, frozen=True)
class Basic:
    a: int
    b: str = "not provided"

def my_program(data: Basic):
    # Your actual program will go here. For this example we just print the input.
    print(data)


if __name__ == "__main__":
    data = clattr.call(Basic)
    my_program(data)

This could be invoked as

python examples/basic.py --a 1 --b hi

clattr will construct this object

Basic(a=1, b='hi')

Which you can then pass into the rest of your code as you please. The example simply prints it and then exits.

Or if you have environment variables defined

export A=1
export B=hi
python example.py

again yields

Basic(a=1, b='hi')

clattr also supports nested objects (or functions taking complex objects as inputs)

from typing import Optional
import datetime as dt

import attr
import clattr


@attr.s(auto_attribs=True, frozen=True)
class Foo:
    a: dt.datetime
    b: Optional[str] = None


@attr.s(auto_attribs=True, frozen=True)
class Bar:
    f: Foo
    c: int

def my_program(data: Bar):
    print(data)

if __name__ == "__main__":
    bar = clattr.call(Bar)
    my_program(bar)

You specify values for the fields in the nested class by referring to them with a their field name in the outer class

python examples/advanced.py --c 1 --f.a 2020-01-01 --f.b hi

Bar(f=Foo(a=1, b='hi'), c=1)

You can also supply one or more json formatted config files. Provide the name(s) of these files as positional arguments. `clattr`` will search them, last file first, for any keys fields that are not provided at the command line before searching the environment.

python examples/advanced.py --c 1 examples/foo.json

Bar(f=Foo(a=1, b='str'), c=1)

clattr is inspired by clout, but I wanted to try being a bit more opinionated to make both the library and code using it simpler.