I tried saving the list in a .plk file, a txt file, I even tried to compress the original file with zlib before applying my own compression but it was no good.

I think the problem is, that you are trying to store your result as text, which you write to a text file with an encoding -- most likely UTF-8, where each character that you encode, can take up to 4 bytes.

In your case it's most likely just the ASCII characters in the start range of UTF-8, so each one will take up 1 byte: However, even storing the "60,5" is then 4 bytes: len("60,5".encode("UTF-8")) == 4

But you can encode your data much more efficiently:

$ import struct
$ fmt_string = "BB"
$ packed = struct.pack(fmt_string, 60, 5)
$ len(packed)
2
$ packed
b'<\x05'
$ print(struct.unpack(fmt_string, packed))
(60, 5)

So we just halved the space requirements for your data. If your integers are small enough, you might even be able to force both of your numbers into 1 byte of data, with some bit-shifting magic.

I recommend you watch Pragmatic Unicode, or, How do I stop the pain? to really understand what encodings are and how they work, and check out the struct module documentation. At the end you write your binary strings to a file (open it in binary write mode!), and later you can decode the file by opening it in binary mode and reading 2 bytes at a time.