How to join entries in a set into one string?

Solution 1:

', '.join(set_3)

The join is a string method, not a set method.

Solution 2:

Sets don't have a join method but you can use str.join instead.

', '.join(set_3)

The str.join method will work on any iterable object including lists and sets.

Note: be careful about using this on sets containing integers; you will need to convert the integers to strings before the call to join. For example

set_4 = {1, 2}
', '.join(str(s) for s in set_4)

Solution 3:

The join is called on the string:

print ", ".join(set_3)

Solution 4:

Nor the set nor the list has such method join, string has it:

','.join(set(['a','b','c']))

By the way you should not use name list for your variables. Give it a list_, my_list or some other name because list is very often used python function.