Python write to file in list format -

I am trying to write a program that will write a list of information in a text file. Here is an example that I have done so far

  f.open ('blah.txt', 'w') x = input ('put something here') y = input ('something Put info = [x], y, z] a = info [0] b = info [1] c = info [2] f.write (a) f.write (here) b) F.Litat (C) F . However, I need to type it in a list-like format so that I can input  
  x = 1 y = 2 z = 3   
 then the file will be read  
  1,2,3   
 and so the next time I give input information I will write it in a new line  
  1,2,3 4,5,6   
 How can I fix this?   
 
 
 Format the string and type it:  
  s = ', '. Include (info) f.write (s + '\ n')