composable.py

"""A composable decorator"""
from functools import wraps


class composable:
    """Decorator that allows chaining of simple functions"""

    def __init__(self, func: callable):
        self.func = func
        wraps(func)(self)

    def __call__(self, *args, **kwargs):
        """Called when the function is called directly"""
        return self.func(*args, **kwargs)

    def __or__(self, on_the_right):
        """Called when a chain is being stored for later use"""
        if callable(on_the_right):
            return composable(lambda value: on_the_right(self.func(value)))
        return composable(lambda: self.func(on_the_right))

    def __ror__(self, on_the_left):
        """Called when static values are piped into the function"""
        return self.func(on_the_left)

# Note:
# Under normal circumstances, when you call `a | b`, Python will effectively
# attempt to call `a.__or__(b)`.  If a doesn't implement `__or__`, or if a
# `NotImplemented` is returned, Python will then attempt to call `b.__ror__(a)`
# as a fallback.