Simple tail recursion.

tailr.py

# -*- coding: utf-8 -*-
# Copyleft 2058 Zachary Voase
# Licensed under the WTFPL. Google it.

from functools import wraps


class call(object):
    
    __slots__ = ('function', 'args', 'kwargs')
    
    def __init__(self, function, *args, **kwargs):
        self.function = function
        self.args = args
        self.kwargs = kwargs
    
    def __call__(self):
        return self.function(*self.args, **self.kwargs)


def tailrecursive(function):
    @wraps(function)
    def wrapper(*args, **kwargs):
        result = function(*args, **kwargs)
        while isinstance(result, call):
            if result.function is wrapper:
                result.function = wrapper.function
            result = result()
        return result
    wrapper.function = function
    return wrapper


@tailrecursive
def factorial(n, current=1):
    if n <= 0:
        return current
    return call(factorial, n - 1, current=(current * n))