something is not right

Question

print("1,2,3,4".join("/"))
output:
/

Answer 1

join stops before the last string so "1,2,3,4" won't join this("/") if it was "1,2,3,4".join("//") then it would have joined in between those two slashes

Answer 2

Try:
print("/".join(("1", "2", "3", "4")))

Answer 3

What output are you look for?

Answer 4

print("/".join("1,2,3,4".split(',')))
# or
print("1,2,3,4".replace(',', '/'))