Partial application and piping without magic

partial_and_pipe.py

from functools import wraps


class Partial:
    def __init__(self, fn, args, kwargs):
        self._fn = fn
        self._args = args
        self._kwargs = kwargs

    def __call__(self, replacement):
        args = [replacement if arg is ... else arg
                for arg in self._args]
        kwargs = {key: replacement if val is ... else val
                  for key, val in self._kwargs.items()}
        return self._fn(*args, **kwargs)

    def __rmatmul__(self, replacement):
        return self(replacement)

    def __repr__(self):
        return '<Partial: {}(*{}, **{})>'.format(
            self._fn.__name__, repr(self._args), repr(self._kwargs))


def ellipsis_partial(fn):
    @wraps(fn)
    def wrapper(*args, **kwargs):
        ellipsises = (list(args) + list(kwargs.values())).count(...)
        if ellipsises > 1:
            raise TypeError('Only one ... allowed as an argument.')
        elif ellipsises:
            return Partial(fn, args, kwargs)
        else:
            return fn(*args, **kwargs)

    return wrapper


def _(fn, *args, **kwargs):
    return ellipsis_partial(fn)(*args, **kwargs)