There seems to be something wrong with the code below; im not sure if it is the indentations because im getting a different result each time if i change the indents; I'm not sure which is the correct way to indent.

 fh = open("df_1.csv")
 readr = csv.reader(fh) 
 header = next(readr)
 header
 data = [row for row in readr]
 names = set()
  for row in data : 
   mapID = row[1]
     for n in mapID :
    names.add(n) 
 len(names)