Proof of concept for an API providing more "English-like" function calls

curry_helper.py

"""Proof of concept for an API providing "English-like" function calls.

See original python-ideas [thread](https://mail.python.org/archives/list/[email protected]/thread/YMFRX6K22TZNNAP2PPVV7RGNI5HLC764/#WF232SOAJJWM33ZAY327OAPCONFOUXVX).

API:

```
from curry_helper import curry_helper

# apply the curry_helper decorator with a list of function "suffixes"
# each argument after the first argument corresponds to a single suffix 
@curry_helper(suffixes=["a", "b"]
def f(x, y, z):
    ...  # TODO

f(x).a(y).b(z)
```
"""

from functools import partial
from inspect import signature


def curry_helper(func=None, *, suffixes):
    if func is None:
        return partial(curry_helper, suffixes=suffixes)

    return CurryHelper(func, suffixes)


class CurryHelper:

    def __init__(self, func, suffixes):
        self._func = func
        self._nparams = len(signature(func).parameters)
        self._suffixes = set(suffixes)
        if self._nparams-1 != len(self._suffixes):
            raise Exception("the number of suffixes must match the number of function arguments, less 1")

    def __getattr__(self, attr):
        ...  # TODO

    def __call__(self, arg=None):
        return CalledCurryHelper(self, arg)


class CalledCurryHelper:

    def __init__(self, curry_helper, arg):
        self._args = [arg]
        self._curry_helper = curry_helper

    def __call__(self, arg):
        self._args.append(arg)
        if len(self._args)==self._curry_helper._nparams:
            return self._curry_helper._func(*self._args)
        return self

    def __getattr__(self, attr):
        if attr in self._curry_helper._suffixes:
            return self
        raise AttributeError(f"{type(self).__name__!r} object has no attribute {attr!r}")


if __name__=="__main__":
    from typing import Any

    @curry_helper(suffixes=["into"])
    def insert(x: Any, y: list):
        y.append(x)


    item = 1
    container = []
    insert(item).into(container)
    assert container == [item]

    @curry_helper(suffixes=["an_instance_of_"])
    def is_(obj, cls):
        return isinstance(obj, cls)

    obj = 1
    assert is_(obj).an_instance_of_(int)

    @curry_helper(suffixes=["a", "b"])
    def f(x, y, z):
        ...  # TODO

    x,y,z = None,None,None
    assert f(x).a(y).b(z) is None