Join integer value

While working with csv module of python i got very interesting thing about join.
I was reading a huge csv file line by line and for some kind of operation i converted that row to list and again that list to string. But, my row consists of some integer values so i always get
TypeError: sequence item 5: expected string, int found

So, i am writing small code to let new guys know about this.
i have a list and i want to join this.
ls=['a','b',4,'c']
','.join(ls)
ends up with  : TypeError: sequence item 2: expected string, int found

do,
','.join(map(str,ls))