from functools import  reduce
def left_join(phrases):
    alist = [x for x  in phrases]
    for i in range(len(alist)) :
        if "right" in alist[i]:
            alist[i]=alist[i].replace("right","left")
    return reduce(lambda x,y:x+","+y,alist)

if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    assert left_join(("left", "right", "left", "stop")) == "left,left,left,stop", "All to left"
    assert left_join(("bright aright", "ok")) == "bleft aleft,ok", "Bright Left"
    assert left_join(("brightness wright",)) == "bleftness wleft", "One phrase"
    assert left_join(("enough", "jokes")) == "enough,jokes", "Nothing to replace"
    print("Coding complete? Click 'Check' to review your tests and earn cool rewards!")