[CheckIO] Right to Left

Problems: py.checkio.org/en/mission/right-to-left/

My solution:

import re
def left_join(phrases: tuple) -> str:
    """
        Join strings and replace "right" to "left"
    """
    dummy = ""
    for string in phrases:
        dummy = dummy + re.sub('right', 'left', string) + ","
    return dummy[:-1]

if __name__ == '__main__':
    print('Example:')
    print(left_join(("left", "right", "left", "stop")))
    
    #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!")

A good solution that I see

def left_join(phrases):
    """
        Join strings and replace "right" to "left"
    """
    return (",".join(phrases)).replace("right","left")