How to convert a list to a comma separated string?

Using a for loop I get the data:

58738121385139B9135A4251EF02B631B53C383

I'm trying to get this data into one line separated by commas using

a = ', '.join(b);

but I get a comma after every character 5,8,7,3,8,1,2,1...Please tell me how to get data 58738121385139B,9135A4251EF0,2B631B53C383 of this type.