def left_join(phrases):

"""

Join strings and replace "right" to "left"

"""

s = 0

a = ''

for i in phrases:

while 'right' in i:

s = i.index('right')

i = i[:s] + 'left' + i[s+5:]

a += i +','

# print(b)

return a.strip(',')

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!")