#/usr/bin/env python3
 
def fold(function, value, iterable, /, *, reverse = None):
    it = (reversed if reverse else iter)(iterable)
    args = lambda value, element: (value, element) if reverse == False else \
           (element, value)
    for element in it:
        value = function(*args(value, element))
    return value
 
if __name__ == '__main__':
    from operator import add
    z = 'z'
    print(f'{fold(add, z, ["a", "b", "c", "d"])}\n{fold(add, z, ["a", "b", "c", "d"], reverse = True)}\n{fold(add, z, ["a", "b", "c", "d"], reverse = False)}')
 

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